Atmospheric Environment (v.140, #C)

Particulate hydroxy-PAH emissions from a residential wood log stove using different fuels and burning conditions by Rozanna Avagyan; Robin Nyström; Robert Lindgren; Christoffer Boman; Roger Westerholm (1-9).
Hydroxylated polycyclic aromatic hydrocarbons are oxidation products of polycyclic aromatic hydrocarbons, but have not been studied as extensively as polycyclic aromatic hydrocarbons. Several studies have however shown that hydroxylated polycyclic aromatic hydrocarbons have toxic and carcinogenic properties. They have been detected in air samples in semi urban areas and combustion is assumed to be the primary source of those compounds. To better understand the formation and occurrence of particulate hydroxylated polycyclic aromatic hydrocarbons from residential wood log stove combustion, 9 hydroxylated polycyclic aromatic hydrocarbons and 2 hydroxy biphenyls were quantified in particles generated from four different types of wood logs (birch, spruce, pine, aspen) and two different combustion conditions (nominal and high burn rate). A previously developed method utilizing liquid chromatography – photo ionization tandem mass spectrometry and pressurized liquid extraction was used. Polycyclic aromatic hydrocarbons were analyzed along with hydroxylated polycyclic aromatic hydrocarbons. The hydroxylated polycyclic aromatic hydrocarbon emissions varied significantly across different wood types and burning conditions; the highest emissions for nominal burn rate were from spruce and for high burn rate from pine burning. Emissions from nominal burn rate corresponded on average to 15% of the emissions from high burn rate, with average emissions of 218 μg/MJfuel and 32.5 μg/MJfuel for high burn rate and nominal burn rate, respectively. Emissions of the measured hydroxylated polycyclic aromatic hydrocarbons corresponded on average to 28% of polycyclic aromatic hydrocarbons emissions.This study shows that wood combustion is a large emission source of hydroxylated polycyclic aromatic hydrocarbons and that not only combustion conditions, but also wood type influences the emissions of hydroxylated polycyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons. There are few studies that have determined hydroxylated polycyclic aromatic hydrocarbons in emissions from wood combustion, and it is therefore necessary to further investigate the formation, occurrence and distribution of these compounds as they are present in significant amounts in wood smoke particles.
Keywords: OH-PAHs; Hydroxy-PAHs; PAHs; Wood combustion; Wood burning; Wood log stove;

The present study uses a back-trajectory analysis at multiple heights for better interpretation of the impact of the African dust outbreaks in the coastal Mediterranean city of Málaga (Spain), the southernmost large city in Europe. Throughout a 3-year period, 363 days were identified as dusty days by atmospheric transport models. During these events, PM10, SO2, O3, temperature, AOD and Ångström exponent showed statistically significant differences compared to days with no African dust. It was found that under African dust events, the study site was influenced by Mediterranean air masses at the lowermost heights and by Atlantic advections at high altitudes, while African air masses mostly reached Málaga at intermediate levels. Specifically, the lowest heights at which air masses reached the study site after having resided over Africa are confined into the 1000–2000 m range. The decoupling between the lowest heights and the ones for dust transport may explain the presence of aged air masses at the time of the African outbreak. Additionally, with the aim of studying the influence of the air mass origin and history on air quality, a new procedure based on Principal component analysis (PCA) is proposed to determine which altitudes are best suited as starting points for back-trajectory calculations, as they maximize the differences in residence time over different areas. Its application to Málaga identifies three altitudes (750, 2250 and 4500 m) and a subsequent analysis of back-trajectories for African dust days provided the main source areas over Africa as well as further insight on the Mediterranean contribution.
Keywords: African dust outbreak; Dust; Aged pollutants; Back-trajectory analysis;

Assessment of the spatial and temporal distribution of persistent organic pollutants (POPs) in the Nordic atmosphere by Pia Anttila; Eva Brorström-Lundén; Katarina Hansson; Hannele Hakola; Mika Vestenius (22-33).
Long-term atmospheric monitoring data (1994–2011) of persistent organic pollutants (POPs) were assembled from a rural site in southern Sweden, Råö, and a remote, sub-Arctic site in Finland, Pallas. The concentration levels, congener profiles, seasonal and temporal trends, and projections were evaluated in order to assess the status of POPs in the Scandinavian atmosphere. Our data include atmospheric concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), altogether comprising a selection of 27 different compounds.The atmospheric POP levels were generally higher in the south, closer to the sources (primary emissions) of the pollutants. The levels of low-chlorinated PCBs and chlordanes were equal at the two sites, and one of the studied POPs, α-HCH, showed higher levels in the north than in the south.Declining temporal trends in the atmospheric concentrations for the legacy POPs — PCBs (2–4% per year), HCHs (6–7% per year), chlordanes (3–4% per year) and DTTs (2–5% per year) — were identified both along Sweden’s west coast and in the sub-Arctic area of northern Finland. Most of PAHs did not show any significant long-term trends.The future projections for POP concentrations suggest that in Scandinavia, low-chlorinated PCBs and p,p′-DDE will remain in the atmospheric compartment the longest (beyond 2030). HCH’s and PCB180 will be depleted from the Nordic atmosphere first, before 2020, whereas chlordanes and rest of the PCBs will be depleted between the years 2020 and 2025. PCBs tend to deplete sooner and chlordanes later from the sub-Arctic compared to the south of Sweden.This study demonstrates that the international bans on legacy POPs have successfully reduced the concentrations of these particular substances in the Nordic atmosphere. However, the most long-lived compounds may continue in the atmospheric cycle for another couple of decades.
Keywords: PAHs; PCBs; OCP; Air concentrations; Atmospheric transport; Trends; Scandinavia; South-north gradient; Projections;

Exposure to daily ambient particulate polycyclic aromatic hydrocarbons and cough occurrence in adult chronic cough patients: A longitudinal study by Enoch Olando Anyenda; Tomomi Higashi; Yasuhiro Kambayashi; Nguyen Thi Thu Thao; Yoshimasa Michigami; Masaki Fujimura; Johsuke Hara; Hiromasa Tsujiguchi; Masami Kitaoka; Hiroki Asakura; Daisuke Hori; Yohei Yamada; Koichiro Hayashi; Kazuichi Hayakawa; Hiroyuki Nakamura (34-41).
The specific components of airborne particulates responsible for adverse health effects have not been conclusively identified. We conducted a longitudinal study on 88 adult patients with chronic cough to evaluate whether exposure to daily ambient levels of particulate polycyclic aromatic hydrocarbons (PAH) has relationship with cough occurrence. Study participants were recruited at Kanazawa University Hospital, Japan and were physician-diagnosed to at least have asthma, cough variant asthma and/or atopic cough during 4th January to 30th June 2011. Daily cough symptoms were collected by use of cough diaries and simultaneously, particulate PAH content in daily total suspended particles collected on glass fiber filters were determined by high performance liquid chromatography coupled with fluorescence detector. Population averaged estimates of association between PAH exposure and cough occurrence for entire patients and subgroups according to doctor’s diagnosis were performed using generalized estimating equations. Selected adjusted odds ratios for cough occurrence were 1.088 (95% confidence interval (CI): 1.031, 1.147); 1.209 (95% CI: 1.060, 1.379) per 1 ng/m3 increase for 2-day lag and 6-day moving average PAH exposure respectively. Likewise, 5 ring PAH had higher odds in comparison to 4 ring PAH. On the basis of doctor’s diagnosis, non-asthma group had slightly higher odds ratio 1.127 (95% CI: 1.033, 1.228) per 1 ng/m3 increase in 2-day lag PAH exposure. Our findings suggest that ambient PAH exposure is associated with cough occurrence in adult chronic cough patients. The association may be stronger in non-asthma patients and even at low levels although there is need for further study with a larger sample size of respective diagnosis and inclusion of co-pollutants.
Keywords: Polycyclic aromatic hydrocarbon; Adult patients; Asthma; Generalized estimating equation; Total suspended particles; High performance liquid chromatography;

Long-term variation of the source of sulfate deposition in a leeward area of Asian continent in view of sulfur isotopic composition by Tsuyoshi Ohizumi; Naoko Take; Yayoi Inomata; Hiroaki Yagoh; Tomomi Endo; Masaaki Takahashi; Kazuki Yanahara; Minoru Kusakabe (42-51).
A large emission of air pollutants from the Asian continent has caused transboundary air pollution, especially in northeastern Asia. This paper evaluates sulfate deposition at a leeward area of Asian continent, i.e., the Nagaoka observation station located along the Sea of Japan. We have monitored atmospheric sulfate deposition and its sulfur isotopic ratio for 28 years at the station. The sulfur isotopic ratios of non-sea-salt sulfate (δ34Snss) ranged from 0.0 to +6.2‰. The isotopic ratios of local emission and Chinese coal sulfur showed negative and positive values, respectively. Several statistically significant trends were detected on the deposition of non-sea-salt sulfate (nss-SO4 2−) during the study period. The decrease of nss-SO4 2− deposition since the middle of 1980s was considered to have been caused by local anthropogenic SO2 emission that showed relatively low δ34Snss values during the period. The increase of nss-SO4 2− deposition from the end of 1990s to the second half of 2000s was interpreted to have been caused by the change in SO2 emission in China because the δ34Snss values increased during the period with the winter values getting closer to the averaged value of Chinese coal sulfur. The decreasing trend of nss-SO4 2− deposition from the middle of 2000s was likely affected by reduction of Chinese SO2 emission judging from the decrease in δ34Snss values in the period. Mass balance calculations suggested that sulfur released by coal combustion in China during 1990s contributed by about 40% of annual total sulfur deposition in Nagaoka, and its contribution increased up to 60% in the middle of 2000s. The contribution turned to decrease after that peak, which was in harmony with the temporal change of emission from China.
Keywords: Sulfur isotopic ratio; Sulfate; Acid deposition; Coal combustion; Northeastern Asia;

Air pollution exposure: An activity pattern approach for active transportation by Matthew D. Adams; Nikolaos Yiannakoulias; Pavlos S. Kanaroglou (52-59).
In this paper, we demonstrate the calculation of personal air pollution exposure during trips made by active transportation using activity patterns without personal monitors. We calculate exposure as the inhaled dose of particulate matter 2.5 μg or smaller. Two modes of active transportation are compared, and they include cycling and walking. Ambient conditions are calculated by combining mobile and stationary monitoring data in an artificial neural network space-time model. The model uses a land use regression framework and has a prediction accuracy of R2 = 0.78. Exposure is calculated at 10 m or shorter intervals during the trips using inhalation rates associated with both modes. The trips are children’s routes between home and school. The average dose during morning cycling trips was 2.17 μg, during morning walking trips was 3.19 μg, during afternoon cycling trips was 2.19 μg and during afternoon walking trips was 3.23 μg. The cycling trip dose was significantly lower than the walking trip dose. The air pollution exposure during walking or cycling trips could not be strongly predicted by either the school or household ambient conditions, either individually or in combination. Multiple linear regression models regressing both the household and school ambient conditions against the dose were only able to account for, at most, six percent of the variance in the exposure. This paper demonstrates that incorporating activity patterns when calculating exposure can improve the estimate of exposure compared to its calculation from ambient conditions.
Keywords: Air pollution exposure; Activity analysis; Children’s exposure; Particulate matter;

Number size distributions of atmospheric aerosol particles were simultaneously measured at a kerbside and an urban background site in the city of Thessaloniki, Greece, from June to October 2009. New particle formation events were observed ca. 27% of the days at the urban kerbside site and 29% of the days at the urban background site. In almost all the cases the events started between 10:00 and 12:00, and continued for several hours. The total number concentration (TNC) of the particles having diameters from 10 to ca. 500 nm during the events increased from 1.4 × 104 to 6.5 × 104 #/cm3 at the urban kerbside site, and from 0.2 × 104 to 2.4 × 104 #/cm3 at the urban background site. At the urban kerbside site, 9% of the days exhibited class I events (i.e., events followed by a clear growth of the newly formed particles), 10% class II (i.e., events during which the concentration of nucleation mode particles were high but their growth was not continuous), 67% were characterised as non-event days, and 14% of the days exhibited no clear particle formation pattern (undefined). At the urban background site, 15% of the days were classified as class I, 5% as class II, 75% of the days showed no nucleation, whereas only 5% of the days were undefined. While the fraction of event days (both class I and class II) at both sites was similar (ca. 20%), the higher fraction of class I events observed at Eptapyrgio can be attributed to the cleaner environment of the urban background site that allows better identification of the particle concentration increase. The nucleation bursts show a similar pattern at both sites, with the newly formed particles reaching a final size of ca. 80–100 nm. A distinct difference between the two stations was that the smallest particles observed during the new-particle formation events had a diameter of ca. 10 nm (i.e., the smallest particles we could observe) at the kerbside site and ca. 20 nm at the urban background site. This is an indication that the new particles observed at the urban background station are formed elsewhere and are transported to the site. Estimated concentrations of H2SO4 using a proxy model, suggest that these are high enough to explain the nucleation events despite that the available aerosol surface was high, especially at the urban kerbside site.
Keywords: Nanoparticles; Nucleation; Particle growth;

Factors influencing separation distances against odour annoyance calculated by Gaussian and Lagrangian dispersion models by Martin Piringer; Werner Knauder; Erwin Petz; Günther Schauberger (69-83).
Direction-dependent separation distances to avoid odour annoyance, calculated with the Gaussian Austrian Odour Dispersion Model AODM and the Lagrangian particle diffusion model LASAT at two sites, are analysed and compared. The relevant short-term peak odour concentrations are calculated with a stability-dependent peak-to-mean algorithm. The same emission and meteorological data, but model-specific atmospheric stability classes are used. The estimate of atmospheric stability is obtained from three-axis ultrasonic anemometers using the standard deviations of the three wind components and the Obukhov stability parameter. The results are demonstrated for the Austrian villages Reidling and Weissbach with very different topographical surroundings and meteorological conditions. Both the differences in the wind and stability regimes as well as the decrease of the peak-to-mean factors with distance lead to deviations in the separation distances between the two sites. The Lagrangian model, due to its model physics, generally calculates larger separation distances. For worst-case calculations necessary with environmental impact assessment studies, the use of a Lagrangian model is therefore to be preferred over that of a Gaussian model. The study and findings relate to the Austrian odour impact criteria.
Keywords: Odour; Stability class; Peak-to-mean factor; Separation distance; Ultrasonic anemometer;

Cost-effective reductions of PM2.5 concentrations and exposure in Italy by A. Ciucci; I. D’Elia; F. Wagner; R. Sander; L. Ciancarella; G. Zanini; W. Schöpp (84-93).
In recent years several European air pollution policies have been based on a cost-effectiveness approach. In the European Union, the European Commission starts using the multi-pollutant, multi-effect GAINS (Greenhouse Gas Air Pollution Interactions and Synergies) model to identify cost-effective National Emission Ceilings and specific emission control measures for each Member State to reach these targets. In this paper, we apply the GAINS methodology to the case of Italy with 20 subnational regions. We present regional results for different approaches to environmental target setting for PM2.5 pollution in the year 2030. We have obtained these results using optimization techniques consistent with those of GAINS-Europe, but at a higher resolution. Our results show that an overall health-impact oriented approach is more cost-effective than setting a nation-wide limit value on ambient air quality, such as the one set for the year 2030 by the European Directive on ambient air quality and cleaner air for Europe. The health-impact oriented approach implies additional emission control costs of 153 million €/yr on top of the baseline costs, compared to 322 million €/yr for attaining the nation-wide air quality limit. We provide insights into the distribution of costs and benefits for regions within Italy and identify the main beneficiaries of a health-impact approach over a limit-value approach.
Keywords: Cost-effectiveness analysis; Policy scenario; Integrated assessment models; Air pollution; Environmental target setting approaches; Population exposure;

Physiochemical properties of carbonaceous aerosol from agricultural residue burning: Density, volatility, and hygroscopicity by Chunlin Li; Yunjie Hu; Jianmin Chen; Zhen Ma; Xingnan Ye; Xin Yang; Lin Wang; Xinming Wang; Abdelwahid Mellouki (94-105).
Size-resolved effective density, mixing state, and hygroscopicity of smoke particles from five kinds of agricultural residues burning were characterized using an aerosol chamber system, including a volatility/hygroscopic tandem differential mobility analyzer (V/H-TDMA) combined with an aerosol particle mass analyzer (APM). To profile relationship between the thermodynamic properties and chemical compositions, smoke PM1.0 and PM2.5 were also measured for the water soluble inorganics, mineral elements, and carbonaceous materials like organic carbon (OC) and elemental carbon (EC). Smoke particle has a density of 1.1–1.4 g cm−3, and hygroscopicity parameter (κ) derived from hygroscopic growth factor (GF) of the particles ranges from 0.20 to 0.35. Size- and fuel type-dependence of density and κ are obvious. The integrated effective densities (ρ) and hygroscopicity parameters (κ) both scale with alkali species, which could be parameterized as a function of organic and inorganic mass fraction (f org &f inorg ) in smoke PM1.0 and PM2.5: ρ − 1 = f i n o r g · ρ i n o r g − 1 + f o r g · ρ o r g − 1 and κ = f i n o r g · κ i n o r g + f o r g · κ o r g . The extrapolated values of ρ inorg and ρ org are 2.13 and 1.14 g cm−3 in smoke PM1.0, while the characteristic κ values of organic and inorganic components are about 0.087 and 0.734, which are similar to the bulk density and κ calculated from predefined chemical species and also consistent with those values observed in ambient air. Volatility of smoke particle was quantified as volume fraction remaining (VFR) and mass fraction remaining (MFR). The gradient temperature of V-TDMA was set to be consistent with the splitting temperature in the OC-EC measurement (OC1 and OC2 separated at 150 and 250 °C). Combing the thermogram data and chemical composition of smoke PM1.0, the densities of organic matter (OM1 and OM2 correspond to OC1 and OC2) are estimated as 0.61–0.90 and 0.86–1.13 g cm−3, and the ratios of OM1/OC1 and OM2/OC2 are 1.07 and 1.29 on average, indicating more volatile organic materials have less density and lower OM/OC ratios in the external mixed smoke particles.Display Omitted
Keywords: Smoke particle; Density; Volatility; Hygroscopicity; APM; V/H-TDMA;

Evolution of the Nabro volcanic aerosols from initially-localized plumes to a decaying hemispherically-covered layer was jointly observed by ground-based lidars at Wuhan (30.5°N, 114.4°E), China and CALIPSO. During the aerosol plume formation period, from the Nabro eruption to early July 2011, the lidar backscatter ratio related to the Nabro aerosols above Wuhan varied strongly both in vertical structure and intensity, suggesting that the Nabro aerosol distribution was horizontally inhomogeneous. The stratospheric aerosol optical depth (AOD) from CALIPSO shows that the Nabro plume first circled around the Asian monsoon anticyclone and then gradually fulfilled the whole anticyclone area with a net aerosol enhancement, which may reflect a gas-particle conversion (from sulfur dioxide gas) and/or particle injection from the upper troposphere. During the horizontal dispersion period, from early July to mid-August 2011, the stratospheric AOD over Wuhan declined rapidly since the Nabro particles were transported throughout the northern hemisphere. A nearly horizontally-uniform volcanic aerosol layer was formed. During the local cleansing period, from mid-August to the end of 2011, the Nabro aerosol layer over Wuhan had a single-peak structure and decayed uniformly. The corresponding e-folding decay time for the layer AOD is ∼130 days. The lidar measurements at Wuhan gave a small depolarization ratio and large backscatter-related Ångström exponent for the Nabro aerosols on 8 July, suggesting that the majority of these aerosols were spherical and small. The effective radius and total mass for the Nabro aerosol particles were estimated to be ∼0.26 μm and ∼0.32 Tg respectively.
Keywords: Volcanic aerosols; Lidar; CALIPSO; Evolution; Backscatter ratio; Mass concentration;

Catalytic oxidation of volatile organic compounds (VOCs) – A review by Muhammad Shahzad Kamal; Shaikh A. Razzak; Mohammad M. Hossain (117-134).
Emission of volatile organic compounds (VOCs) is one of the major contributors to air pollution. The main sources of VOCs are petroleum refineries, fuel combustions, chemical industries, decomposition in the biosphere and biomass, pharmaceutical plants, automobile industries, textile manufacturers, solvents processes, cleaning products, printing presses, insulating materials, office supplies, printers etc. The most common VOCs are halogenated compounds, aldehydes, alcohols, ketones, aromatic compounds, and ethers. High concentrations of these VOCs can cause irritations, nausea, dizziness, and headaches. Some VOCs are also carcinogenic for both humans and animals. Therefore, it is crucial to minimize the emission of VOCs. Among the available technologies, the catalytic oxidation of VOCs is the most popular because of its versatility of handling a range of organic emissions under mild operating conditions. Due to that fact, there are numerous research initiatives focused on developing advanced technologies for the catalytic destruction of VOCs. This review discusses recent developments in catalytic systems for the destruction of VOCs. Review also describes various VOCs and their sources of emission, mechanisms of catalytic destruction, the causes of catalyst deactivation, and catalyst regeneration methods.
Keywords: VOCs; Oxidation; Oxidation process; Catalysts; Multicomponent catalysts; Mechanism; Kinetics;

An urban scale inverse modelling for retrieving unknown elevated emissions with building-resolving simulations by Pramod Kumar; Sarvesh Kumar Singh; Amir-Ali Feiz; Pierre Ngae (135-146).
This study illustrates an atmospheric source reconstruction methodology for identification of an unknown continuous point release in the geometrically complex urban environments. The methodology is based on the renormalization inversion theory coupled with a building resolving Computational Fluid Dynamics (CFD) modelling approach which estimates the release height along with the projected location on the ground surface and the intensity of an unknown continuous point source in an urban area. An estimation of the release height in a three-dimensional urban environment is relatively more difficult from both technical and computational point of view. Thus, a salient feature of the methodology is to address the problem of vertical structure (i.e. height of a source) in atmospheric source reconstruction in three-dimensional space of an urban region. The inversion methodology presents a way to utilize a CFD model fluidyn-PANACHE in source reconstruction in the urban regions. The described methodology is evaluated with 20 trials of the Mock Urban Field Setting Test (MUST) field experiment in various atmospheric stability conditions varying from neutral to stable and very stable conditions. The retrieved source parameters in all the 20 trials are estimated close to their true source. The source height is retrieved within a factor of two and four in 55% and 75% of the MUST trials, respectively. The averaged location error for all 20 trials is obtained 14.54 m with a minimum of 3.58 m and maximum of 34.55 m. The averaged estimated release rate for all trials is overpredicted within a factor of 1.48 of the true source intensity and in 85% of the trials, it is retrieved within in factor of two. In source reconstruction with non-zero measurements, it was observed that the use of all concentration measurements instead of only non-zero essentially makes only the small differences in quality of the source reconstruction and gives a little additional information for better constraining the source parameters. A posteriori uncertainty analysis in the retrieved source parameters is also performed by adding a controlled noise in the concentration measurements and the source reconstruction results were also compared with an earlier study based on the stochastic Bayesian approach for identical 14 MUST trials. The study is useful for emergency regulators to detect an unknown accidental or deliberated continuous point releases in urban regions.
Keywords: CFD; Renormalization; Source reconstruction; MUST field experiment; Urban;

New directions: Need for better understanding of source and formation process of phthalic acid in aerosols as inferred from aircraft observations over China by Yan-Lin Zhang; Kimitaka Kawamura; Tomomi Watanabe; Shiro Hatakeyama; Akinori Takami; Wei Wang (147-149).

2014 iAREA campaign on aerosol in Spitsbergen – Part 1: Study of physical and chemical properties by J. Lisok; K.M. Markowicz; C. Ritter; P. Makuch; T. Petelski; M. Chilinski; J.W. Kaminski; S. Becagli; R. Traversi; R. Udisti; A. Rozwadowska; M. Jefimow; P. Markuszewski; R. Neuber; P. Pakszys; I.S. Stachlewska; J. Struzewska; T. Zielinski (150-166).
This paper presents the results of measurements of aerosol physical and chemical properties during iAREA2014 campaign that took place on Svalbard between 15th of Mar and 4th of May 2014. With respect to field area, the experiment consisted of two sites: Ny–Ålesund (78°55′N, 11°56′E) and Longyearbyen (78°13′N, 15°33′E) with further integration of Aerosol Robotic Network (AERONET) station in Hornsund (77°00′N, 15°33′E). The subject of this study is to investigate the in–situ, passive and active remote sensing observations as well as numerical simulations to describe the temporal variability of aerosol single–scattering properties during spring season on Spitsbergen. The retrieval of the data indicates several event days with enhanced single–scattering properties due to the existence of sulphate and additional sea–salt load in the atmosphere which is possibly caused by relatively high wind speed. Optical results were confirmed by numerical simulations made by the GEM–AQ model and by chemical observations that indicated up to 45% contribution of the sea–salt to a PM10 total aerosol mass concentration. An agreement between the in-situ optical and microphysical properties was found, namely: the positive correlation between aerosol scattering coefficient measured by the nephelometer and effective radius obtained from laser aerosol spectrometer as well as negative correlation between aerosol scattering coefficient and the Ångstrom exponent indicated that slightly larger particles dominated during special events. The in–situ surface observations do not show any significant enhancement of the absorption coefficient as well as the black carbon concentration which might occur during spring. All of extensive single–scattering properties indicate a diurnal cycle in Longyearbyen, where 21:00–5:00 data stays at the background level, however increasing during the day by the factor of 3–4. It is considered to be highly connected with local emissions originating in combustion, traffic and harbour activities. On the other hand, no daily fluctuations in Ny–Ålesund are observed. Mean values in Ny–Ålesund are equal to 8.2, 0.8 Mm−1 and 103 ng/m3 for scattering, absorption coefficients and black carbon concentration; however in Longyearbyen (only data from 21:00–05:00 UTC) they reach 7.9, 0.6 Mm−1 as well as 83 ng/m3 respectively. Overall, the spring 2014 was considerably clean and sea–salt was the major aerosol component.
Keywords: Single scattering properties; Chemical composition; Long–range transport; Arctic;

Characterisation of iron-rich atmospheric submicrometre particles in the roadside environment by P. Sanderson; S.S. Su; I.T.H. Chang; J.M. Delgado Saborit; D.M. Kepaptsoglou; R.J.M. Weber; Roy M. Harrison (167-175).
Human exposure to ambient metallic nanoparticles is an area of great interest owing to their potential health impacts. Ambient metallic nanoparticles found in the roadside environment are contributed by combustion engines and wear of brakes, tyres and road surfaces. Submicrometre atmospheric particles collected at two UK urban sites have been subject to detailed characterisation. It is found that many metallic nanoparticles collected from roadside sampling sites are rich in iron. The Fe-rich nanoparticles can be classified into (1) high Fe content (ca 90 wt%) with each alloying element less than 1 wt%; and (2) moderate Fe content (<75 wt%) with high manganese and silicon content. Both clusters contain a variable mix of minor constituents, Mn, S and Si being most important in the high-Fe group. The moderate Fe group also contains Zn, Cu, Ba, Al and Ca. The Fe-rich nanoparticles exhibit primary particle sizes ranging between 20 and 30 nm, although some much larger particles up to around 100 nm can also be observed, along with some very small particles of 10 nm or less. These tend to agglomerate forming clusters ranging from ∼200 nm to 1 μm in diameter. The iron-rich particles observed are oxides, taking the form of spheres or multifaceted regular polyhedra. Analysis by EELS shows that both high- and moderate-Fe groups include particles of FeO, Fe3O4, α-Fe2O3 and γ-Fe2O3 of which γ-Fe2O3 is the most prominent. Internal mixing of different Fe-oxides is not observed.
Keywords: Iron oxide; Nanoparticles; Ultrafine particles; Roadside; Metallic;

Effect of measurement protocol on organic aerosol measurements of exhaust emissions from gasoline and diesel vehicles by Youngseob Kim; Karine Sartelet; Christian Seigneur; Aurélie Charron; Jean-Luc Besombes; Jean-Luc Jaffrezo; Nicolas Marchand; Lucie Polo (176-187).
Exhaust emissions of semi-volatile organic compounds (SVOC) from passenger vehicles are usually estimated only for the particle phase via the total particulate matter measurements. However, they also need to be estimated for the gas phase, as they are semi-volatile. To better estimate SVOC emission factors of passenger vehicles, a measurement campaign using a chassis dynamometer was conducted with different instruments: (1) a constant volume sampling (CVS) system in which emissions were diluted with filtered air and sampling was performed on filters and polyurethane foams (PUF) and (2) a Dekati Fine Particle Sampler (FPS) in which emissions were diluted with purified air and sampled with on-line instruments (PTR-ToF-MS, HR-ToF-AMS, MAAP, CPC). Significant differences in the concentrations of organic carbon (OC) measured by the instruments are observed. The differences can be explained by sampling artefacts, differences between (1) the time elapsed during sampling (in the case of filter and PUF sampling) and (2) the time elapsed from emission to measurement (in the case of on-line instruments), which vary from a few seconds to 15 min, and by the different dilution factors. To relate elapsed times and measured concentrations of OC, the condensation of SVOC between the gas and particle phases is simulated with a dynamic aerosol model. The simulation results allow us to understand the relation between elapsed times and concentrations in the gas and particle phases. They indicate that the characteristic times to reach thermodynamic equilibrium between gas and particle phases may be as long as 8 min. Therefore, if the elapsed time is less than this characteristic time to reach equilibrium, gas-phase SVOC are not at equilibrium with the particle phase and a larger fraction of emitted SVOC will be in the gas phase than estimated by equilibrium theory, leading to an underestimation of emitted OC if only the particle phase is considered or if the gas-phase SVOC are estimated by equilibrium theory. Current European emission inventories for passenger cars do not yet estimate gas-phase SVOC emissions, although they may represent 60% of total emitted SVOC (gas + particle phases).
Keywords: Vehicle emissions; Aerosol modeling; Gas/particle partitioning; Dilution factor; Emission factors;

On the feasibility of monitoring carbon monoxide in the lower troposphere from a constellation of northern hemisphere geostationary satellites: Global scale assimilation experiments (Part II) by Jérôme Barré; David Edwards; Helen Worden; Avelino Arellano; Benjamin Gaubert; Arlindo Da Silva; William Lahoz; Jeffrey Anderson (188-201).
This paper describes the second phase of an Observing System Simulation Experiment (OSSE) that utilizes the synthetic measurements from a constellation of satellites measuring atmospheric composition from geostationary (GEO) Earth orbit presented in part I of the study. Our OSSE is focused on carbon monoxide observations over North America, East Asia and Europe where most of the anthropogenic sources are located. Here we assess the impact of a potential GEO constellation on constraining northern hemisphere (NH) carbon monoxide (CO) using data assimilation. We show how cloud cover affects the GEO constellation data density with the largest cloud cover (i.e., lowest data density) occurring during Asian summer. We compare the modeled state of the atmosphere (Control Run), before CO data assimilation, with the known “true” state of the atmosphere (Nature Run) and show that our setup provides realistic atmospheric CO fields and emission budgets. Overall, the Control Run underestimates CO concentrations in the northern hemisphere, especially in areas close to CO sources. Assimilation experiments show that constraining CO close to the main anthropogenic sources significantly reduces errors in NH CO compared to the Control Run. We assess the changes in error reduction when only single satellite instruments are available as compared to the full constellation. We find large differences in how measurements for each continental scale observation system affect the hemispherical improvement in long-range transport patterns, especially due to seasonal cloud cover. A GEO constellation will provide the most efficient constraint on NH CO during winter when CO lifetime is longer and increments from data assimilation associated with source regions are advected further around the globe.
Keywords: Atmospheric composition; Global scale; Geostationary constellation; Remote sensing; OSSE; Carbon monoxide; CO lifetime; Long-range transport of pollution; Data assimilation;

All-optical automatic pollen identification: Towards an operational system by Benoît Crouzy; Michelle Stella; Thomas Konzelmann; Bertrand Calpini; Bernard Clot (202-212).
We present results from the development and validation campaign of an optical pollen monitoring method based on time-resolved scattering and fluorescence. Focus is first set on supervised learning algorithms for pollen-taxa identification and on the determination of aerosol properties (particle size and shape). The identification capability provides a basis for a pre-operational automatic pollen season monitoring performed in parallel to manual reference measurements (Hirst-type volumetric samplers). Airborne concentrations obtained from the automatic system are compatible with those from the manual method regarding total pollen and the automatic device provides real-time data reliably (one week interruption over five months). In addition, although the calibration dataset still needs to be completed, we are able to follow the grass pollen season. The high sampling from the automatic device allows to go beyond the commonly-presented daily values and we obtain statistically significant hourly concentrations. Finally, we discuss remaining challenges for obtaining an operational automatic monitoring system and how the generic validation environment developed for the present campaign could be used for further tests of automatic pollen monitoring devices.
Keywords: Pollen; Automatic monitoring; Optical methods; Real-time; Supervised learning;

An AERONET-based aerosol classification using the Mahalanobis distance by Patrick Hamill; Marco Giordano; Carolyne Ward; David Giles; Brent Holben (213-233).
We present an aerosol classification based on AERONET aerosol data from 1993 to 2012. We used the AERONET Level 2.0 almucantar aerosol retrieval products to define several reference aerosol clusters which are characteristic of the following general aerosol types: Urban-Industrial, Biomass Burning, Mixed Aerosol, Dust, and Maritime. The classification of a particular aerosol observation as one of these aerosol types is determined by its five-dimensional Mahalanobis distance to each reference cluster. We have calculated the fractional aerosol type distribution at 190 AERONET sites, as well as the monthly variation in aerosol type at those locations. The results are presented on a global map and individually in the supplementary material. Our aerosol typing is based on recognizing that different geographic regions exhibit characteristic aerosol types. To generate reference clusters we only keep data points that lie within a Mahalanobis distance of 2 from the centroid. Our aerosol characterization is based on the AERONET retrieved quantities, therefore it does not include low optical depth values. The analysis is based on “point sources” (the AERONET sites) rather than globally distributed values. The classifications obtained will be useful in interpreting aerosol retrievals from satellite borne instruments.
Keywords: Atmospheric aerosols; Aerosol typing; AERONET; Mahalanobis distance; Seasonal aerosol variation; High AOD events;

Role of transport in elevated CO levels over Delhi during onset phase of monsoon by Reka Srinivas; Gufran Beig; Sunil K. Peshin (234-241).
While local anthropogenic emission sources contribute significantly to pollutant levels in a megacity Delhi, meteorology can significantly modulate carbon monoxide (CO) levels. We hereby demonstrate that the concentration of CO during the unusual onset of monsoon 2013 was dramatically elevated and crossed the permissible limit (1.7 ppmv) for about a month long-period as against normal onset of monsoon where CO concentration generally drops down significantly. We compare level of CO in 2013 with normal monsoon year 2012. We provide a hypothesis to interpret this long lasting high concentration CO episode and validate using interactive high resolution WRF-Chem model. The model indicates that the high CO episode was caused by an unusually active Bay of Bengal branch of monsoon which bounces off from the east and transports CO rich air from the eastern part of the Indo Gangetic Plains to Delhi.Display OmittedAir masses from CO rich eastern Indo Gangetic Plains lead to CO pollution over Delhi in 2013.
Keywords: Carbon monoxide; Monsoon; Pollution; Land-mass; Indo-Gangetic Plain;

SIRANERISK: Modelling dispersion of steady and unsteady pollutant releases in the urban canopy by L. Soulhac; G. Lamaison; F.-X. Cierco; N. Ben Salem; P. Salizzoni; P. Mejean; P. Armand; L. Patryl (242-260).
SIRANERISK is an operational model for the simulation of the dispersion of unsteady atmospheric releases of pollutant within and above an urban area. SIRANERISK is built on the same principles as the SIRANE model, and couples a street network model for the pollutant transfers within the urban canopy with a Gaussian puff model for the transfers above it. The performance of the model are here analysed by a detailed comparisons with wind-tunnel experiments. These experiments concern the dispersion of steady and unsteady pollutant releases within and above obstacle arrays with varying geometrical configurations, representing different topologies of idealised urban districts. The overall good agreement between numerical and experimental data demonstrates the reliability of SIRANERISK as an operational tool for the assessment of risk analysis and for the management of crises due to the accidental release of harmful airborne pollutants within a built environment.Display Omitted
Keywords: Accidental releases; Model validation; Turbulent dispersion; Urban boundary layer; Wind tunnel experiments;

Long-term comparative study of columnar and surface mass concentration aerosol properties in a background environment by Y.S. Bennouna; V.E. Cachorro; D. Mateos; M.A. Burgos; C. Toledano; B. Torres; A.M. de Frutos (261-272).
The relationship between columnar and surface aerosol properties is not a straightforward problem. The Aerosol Optical Depth (AOD), Ångström exponent (AE), and ground-level Particulate Matter (PMX, x = 10 or 2.5 μm) data have been studied from a climatological point of view. Despite the different meanings of AOD and PMx both are key and complementary quantities that quantify aerosol load in the atmosphere and many studies intend to find specific relationships between them. Related parameters such as AE and PM ratio (PR = PM2.5/PM10), giving information about the predominant particle size, are included in this study on the relationships between columnar and surface aerosol parameters. This study is based on long measurement records (2003–2014) obtained at two nearby background sites from the AERONET and EMEP networks in the north-central area of Spain. The climatological annual cycle of PMx shows two maxima along the year (one in late-winter/early-spring and another in summer), but this cycle is not followed by the AOD which shows only a summer maximum and a nearly bell shape. However, the annual means of both data sets show strong correlation (R = 0.89) and similar decreasing trends of 40% (PM10) and 38% (AOD) for the 12-year record. PM10 and AOD daily data are moderately correlated (R = 0.58), whereas correlation increases for monthly (R = 0.74) and yearly (R = 0.89) means. Scatter plots of AE vs. AOD and PR vs. PM10 have been used to characterize aerosols over the region. The PR vs. AE scatterplot of daily data shows no correlation due to the prevalence of intermediate-sized particles. As day-to-day correlation is low (especially for high turbidity events), a binned analysis was also carried out to establish consistent relationships between columnar and surface quantities, which is considered to be an appropriate approach for environmental and climate studies. In this way the link between surface concentrations and columnar remote sensing data is shown to provide useful information for aerosol characterization from a climatological context, despite some limitations.The relationships between surface and columnar aerosol properties are strongly impacted by high turbidity events. The best correlations are obtained for the annual scale.
Keywords: Aerosol optical depth; Particulate matter; High turbidity events; Columnar and surface relationships; Aerosol climatology;

Assessment of satellite-based aerosol optical depth using continuous lidar observation by C.Q. Lin; C.C. Li; A.K.H. Lau; Z.B. Yuan; X.C. Lu; K.T. Tse; J.C.H. Fung; Y. Li; T. Yao; L. Su; Z.Y. Li; Y.Q. Zhang (273-282).
Due to a reliance on solar radiation, the aerosol optical depth (AOD) is observed only during the day by passive satellite-based instruments such as the MODerate resolution Imaging Spectroradiometer (MODIS). Research on urban air quality, atmospheric turbidity, and evolution of aerosols in the atmospheric boundary layer, however, requires 24-h measurement of aerosols. A lidar system is capable of detecting the vertical distribution of the aerosol extinction coefficient and calculating the AOD throughout the day, but routinely lidar observation is still quite limited and the results from MODIS and lidar sometimes are contradictory in China. In this study, long-term lidar observations from 2005 to 2009 over Hong Kong were analyzed with a focus on identification of the reasons for different seasonal variation in the AOD data obtained from MODIS and lidar. The lidar-retrieved AOD shows the lowest average level, but has the most significant diurnal variation during the summer. When considering only a 5-h period between 10:00 a.m. and 3:00 p.m. local time to match satellite passages, the average of the lidar-retrieved AOD doubles during the summer and exceeds that during the winter. This finding is consistent with the MODIS observation of a higher AOD during the summer and a lower AOD during the winter. The increase in the aerosol extinction coefficient in the upper level of the mixing layer makes the greatest contribution to the increase in the AOD at midday during the summer. These assessments suggest that large over-estimation may occur when long-term averages of AOD are estimated from passive satellite observations.
Keywords: MODIS; Lidar; Aerosol optical depth; Aerosol extinction coefficient; Hong Kong;

OMI/Aura UV product validation using NILU-UV ground-based measurements in Thessaloniki, Greece by Melina-Maria Zempila; Maria-Elissavet Koukouli; Alkiviadis Bais; Ilias Fountoulakis; Antti Arola; Natalia Kouremeti; Dimitris Balis (283-297).
The main aim of this work is to evaluate the NASA EOS AURA Ozone Monitoring Instrument (OMI) UV irradiance estimates through ground-based measurements performed by a NILU-UV multichannel radiometer (NILU-UV) operating in Thessaloniki, Greece, for the time period between January 2005 and December 2014. NILU-UV multi-filter radiometers can provide measurements at 5 UV wavelength bands with full width at half maximum (FWHM) of 10 nm approximately and a time analysis of 1 min. An additional channel measuring the Photosynthetically Active Radiation (PAR) is also incorporated to the instrument and is used for the stringent characterization of the cloud free instances. The OMI instrument estimates solar UV irradiances at four wavelengths close to those of the NILU-UV in Thessaloniki. Clear and all-sky overpass-time, as well as solar local-noon time, UV estimates are provided by the NASA Aura Data Validation Center. Spectra measured from a collocated MKIII Brewer spectrophotometer with serial number 086 (Brewer #086) were utilized for the whole period (2005–2014) in order to estimate the NILU-UV irradiances at the OMI wavelength irradiances and therefore provide a direct comparison and validation to the NILU UV measurements provided by OMI.For the nominal comparisons, using un-flagged OMI data within a 50 km radius from Thessaloniki, the linear determination coefficient, R2, ranges between 0.91 and 0.97 for the 305 nm and between 0.75 and 0.92 for 380 nm depending on the choice of overpass or local-noon time data and the cloudiness flags. The best agreement is found for the clear-sky overpass-time comparisons as well as the both PAR- and satellite algorithm-deduced clear-sky overpass and local-noon comparisons for all wavelengths.The OMI irradiances were found to overestimate the NILU-UV observations in Thessaloniki between ∼4.5% and 13.5% for the 305 nm and between ∼1.5% and ∼10.0% for the 310 nm wavelength depending on the choice of time [overpass vs local noon] and cloudiness restrictions [only satellite-deduced or both PAR- and satellite-deduced]. For the 324 nm and 380 nm wavelengths, the satellite-deduced local-noon time clear skies comparisons show a satellite under-estimation of −3.75% and −4.15% respectively whereas the overpass-time comparisons range between −1.55% and −1.90% for the same wavelengths. When imposing the PAR-deduced clear-sky assessment as well, the comparisons show a satellite over-estimation of 2.50% and 2.75% for the local-noon and 3.70% and 4.10% for the overpass-time cases for the 324 nm and 380 nm wavelengths.The effect of a stricter radius of collocation selection (10 km and 25 km vs 50 km) appears to have a negligible impact on the comparisons however results in a smaller statistical sample. When flagging restrictions are applied to the quality indicators of the OMI data, the amount of co-locations decreases appreciatively but the correlations improve for most cases (R2 > 0.9 in most cases and wavelengths). The effect of the temporal averaging window of the ground-based measurements, of around 10 and 60 min to the overpass time, was also investigated. The differences of the time averaging span result in a more obvious improvement of the agreement for the all-sky cases; the R2 factor improves to 0.94, 0.90, 0.87 and 0.85 from the original 0.91, 0.87, 0.82 and 0.78 for the local-noon comparisons and to 0.96, 0.94, 0.92 and 0.91 from the original 0.93, 0.90, 0.80 and 0.83 for the overpass-time comparisons for the 305 nm, 310 nm, 324 nm and 380 nm wavelengths respectively. Hence, it is shown that this type of temporal averaging can implicitly compensate for the changes of cloud position and optical properties when comparing UV measurements from ground and space.For the detection of the seasonal characteristics of the satellite irradiances it was shown that the 380 nm wavelength can be safely studied. The standard deviation of the strict cloud free overpass-time comparisons of ±12% may form a dependable measure of the seasonality imposed by the satellite retrieval algorithm assumptions. Additionally, the aerosol load at 340 nm and the possible solar zenith angle (SZA) effect on the comparisons was considered. No marked aerosol dependence was found with the ratio of satellite-to-ground irradiances remaining 1.1 ± 1.3 for the all-sky comparisons and 1 ± 0.1 for the clear-sky comparisons, while the SZA effect becomes appreciable only for angles higher than 70° with ratios 1.1 ± 1.0 for all-skies and 1.0 ± 0.1 for the clear-sky cases below that threshold.
Keywords: Ultraviolet irradiance; NILU-UV; OMI; Brewer;

The relationships between insoluble precipitation residues, clouds, and precipitation over California’s southern Sierra Nevada during winter storms by Jessie M. Creamean; Allen B. White; Patrick Minnis; Rabindra Palikonda; Douglas A. Spangenberg; Kimberly A. Prather (298-310).
Ice formation in orographic mixed-phase clouds can enhance precipitation and depends on the type of aerosols that serve as ice nucleating particles (INPs). The resulting precipitation from these clouds is a viable source of water, especially for regions such as the California Sierra Nevada. Thus, a better understanding of the sources of INPs that impact orographic clouds is important for assessing water availability in California. This study presents a multi-site, multi-year analysis of single-particle insoluble residues in precipitation samples that likely influenced cloud ice and precipitation formation above Yosemite National Park. Dust and biological particles represented the dominant fraction of the residues (64% on average). Cloud glaciation, determined using satellite observations, not only depended on high cloud tops (>5.9 km) and low temperatures (<−23 °C), but also on the presence of what were likely dust and biological INPs. The greatest prevalence of ice-phase clouds occurred in conjunction with biologically-rich residues and mineral dust rich in calcium, followed by iron and aluminosilicates. Dust and biological particles are known to be efficient INPs, thus these residues likely influenced ice formation in clouds above the sites and subsequent precipitation quantities reaching the surface during events with similar meteorology. The goal of this study is to use precipitation chemistry information to gain a better understanding of the potential sources of INPs in the south-central Sierra Nevada, where cloud-aerosol-precipitation interactions are poorly understood and where mixed-phase orographic clouds represent a key element in the generation of precipitation and thus the water supply in California.
Keywords: Aerosol-cloud-precipitation interactions; Ice nucleation; Cloud glaciation; Sierra nevada;

Impact of various emission control schemes on air quality using WRF-Chem during APEC China 2014 by Jianping Guo; Jing He; Hongli Liu; Yucong Miao; Huan Liu; Panmao Zhai (311-319).
Emission control measures have been implemented to make air quality good enough for Asia-Pacific Economic Cooperation (APEC) China 2014, which provides us with an ideal test-bed to determine how these measures affect air quality in Beijing and surrounding areas. Based on hourly observations at eight monitoring sites of Beijing, the concentrations of other primary atmospheric pollutants during APEC were found to have significantly lower magnitudes than those before APEC, with the exception of a higher O3 concentration. Overall, WRF/Chem reproduced the observed time series of PM2.5, PM10, NO2, CO, and O3 notably well. To investigate the impact of emission control measures on air quality on both local and regional scales, four emission control schemes were developed according to the locations where emission reduction had taken place; the corresponding simulations were subsequently run separately. Scheme S2 (emission control implemented in Beijing) resulted in reductions of 22%, 24%, 10% and 22% for the concentrations of PM2.5, PM10, NO2 and CO, respectively, compared with 14%, 14%, 8%, and 13% for scheme S3 (emission controls implemented from outside of Beijing). This finding indicates that the local emission reduction in Beijing contributes more to the improved air quality in Beijing during APEC China 2014 than does the emission reduction from outside of Beijing. In terms of the impact on the regional scale, the real emission control scheme led to significant reduction of PM2.5 throughout the whole domain. Although the regional impact cannot be completely ignored, both emission reduction measures implemented in Beijing and those implemented outside of Beijing favor greater reduction in PM2.5 in the domains where measurements are presumably taken, as compared with other domains. Therefore, to improve the air quality in Beijing, more coordinated efforts should be made, particularly in the aspect of more stringent reduction and control strategies on pollutant emission sources across the NCP.
Keywords: WRF/Chem; APEC; PM2.5; Air quality; Emission reduction scheme;

Estimation of excess mortality due to long-term exposure to PM2.5 in Japan using a high-resolution model for present and future scenarios by Daisuke Goto; Kayo Ueda; Chris Fook Sheng Ng; Akinori Takami; Toshinori Ariga; Keisuke Matsuhashi; Teruyuki Nakajima (320-332).
Particulate matter with a diameter of less than 2.5 μm, known as PM2.5, can affect human health, especially in elderly people. Because of the imminent aging of society in the near future in most developed countries, the human health impacts of PM2.5 must be evaluated. In this study, we used a global-to-regional atmospheric transport model to simulate PM2.5 in Japan with a high-resolution stretched grid system (∼10 km for the high-resolution model, HRM) for the present (the 2000) and the future (the 2030, as proposed by the Representative Concentrations Pathway 4.5, RCP4.5). We also used the same model with a low-resolution uniform grid system (∼100 km for the low-resolution model, LRM). These calculations were conducted by nudging meteorological fields obtained from an atmosphere-ocean coupled model and providing emission inventories used in the coupled model. After correcting for bias, we calculated the excess mortality due to long-term exposure to PM2.5 among the elderly (over 65 years old) based on different minimum PM2.5 concentration (MINPM) levels to account for uncertainty using the simulated PM2.5 distributions to express the health effect as a concentration-response function. As a result, we estimated the excess mortality for all of Japan to be 31,300 (95% confidence intervals: 20,700 to 42,600) people in 2000 and 28,600 (95% confidence intervals: 19,000 to 38,700) people in 2030 using the HRM with a MINPM of 5.8 μg/m3. In contrast, the LRM resulted in underestimates of approximately 30% (for PM2.5 concentrations in the 2000 and 2030), approximately 60% (excess mortality in the 2000) and approximately 90% (excess mortality in 2030) compared to the HRM results. We also found that the uncertainty in the MINPM value, especially for low PM2.5 concentrations in the future (2030) can cause large variability in the estimates, ranging from 0 (MINPM of 15 μg/m3 in both HRM and LRM) to 95,000 (MINPM of 0 μg/m3 in HRM) people.
Keywords: Excess mortality in Japan; Long-term exposure to PM2.5; Aerosol transport model; Future scenario; Spatial resolution;

Better understanding the transport mechanisms of organophosphorus flame-retardants (OPFRs) in the residential environment is important to more accurately estimate their indoor exposure and develop risk management strategies that protect human health. This study describes an improved dual small chamber testing method to characterize the sorption of OPFRs on indoor building materials and consumer products. The OPFRs studied were tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP). The test materials and products used as sinks include concrete, ceiling tile, vinyl flooring, carpet, latex painted gypsum wallboard, open cell polyurethane foam, mattress pad and liner, polyester clothing, cotton clothing, and uniform shirt. During the tests, the amount of OPFRs absorbed by the materials at different exposure times was determined simultaneously. OPFRs air concentrations at the inlet and inside the test chamber were monitored. The data were used to rank the sorption strength of the OPFRs on different materials. In general, building materials exhibited relatively stronger sorption strength than clothing textiles. The material-air partition and material phase diffusion coefficients were estimated by fitting a sink model to the sorption concentration data for twelve materials with three OPFRs. They are in the range of 2.72 × 105 to 3.99 × 108 (dimensionless) for the material-air partition coefficients and 1.13 × 10−14 to 5.83 × 10−9 (m2/h) for the material phase diffusion coefficients.
Keywords: Organophosphorus flame retardants; Material-air partition coefficient; Material-phase diffusion coefficient; Sink; Sorption strength;

The U.S. National Oceanic and Atmospheric Administration (NOAA) is responsible for forecasting elevated levels of air pollution within the National Air Quality Forecast Capability (NAQFC). The current research uses measurements gathered in the DISCOVER-AQ Colorado field campaign and the concurrent Front Range Air Pollution and Photochemistry Experiment (FRAPPE) to test performance of the NAQFC CMAQ modeling framework for predicting NH3. The DISCOVER-AQ and FRAPPE field campaigns were carried out in July and August 2014 in Northeast Colorado. Model predictions are compared with measurements of NH3 gas concentrations and the NH4 + component of fine particulate matter concentrations measured directly by the aircraft in flight. We also compare CMAQ predictions with NH3 measurements from ground-based monitors within the DISCOVER-AQ Colorado geographic domain, and from the Tropospheric Emission Spectrometer (TES) on the Aura satellite. In situ aircraft measurements carried out in July and August of 2014 suggest that the NAQFC CMAQ model underestimated the NH3 concentration in Northeastern Colorado by a factor of ∼2.7 (NMB = −63%). Ground-level monitors also produced a similar result. Average satellite-retrieved NH3 levels also exceeded model predictions by a factor of 1.5–4.2 (NMB = −33 to −76%). The underestimation of NH3 was not accompanied by an underestimation of particulate NH4 +, which is further controlled by factors including acid availability, removal rate, and gas-particle partition. The average measured concentration of NH4 + was close to the average predication (NMB = +18%).Seasonal patterns measured at an AMoN site in the region suggest that the underestimation of NH3 is not due to the seasonal allocation of emissions, but to the overall annual emissions estimate. The underestimation of NH3 varied across the study domain, with the largest differences occurring in a region of intensive agriculture near Greeley, Colorado, and in the vicinity of Denver. The NAQFC modeling framework did not include a recently developed bidirectional flux algorithm for NH3, which has shown to considerably improve NH3 modeling in agricultural regions. The bidirectional flux algorithm, however, is not expected to obtain the magnitude of this increase sufficient to overcome the underestimation of NH3 found in this study. Our results suggest that further improvement of the emission inventories and modeling approaches are required to reduce the bias in NAQFC NH3 modeling predictions.
Keywords: NH3; Ammonia; Model evaluation; CMAQ; Aircraft measurement; Remote sensing;

Predicting vehicular emissions in high spatial resolution using pervasively measured transportation data and microscopic emissions model by Marguerite Nyhan; Stanislav Sobolevsky; Chaogui Kang; Prudence Robinson; Andrea Corti; Michael Szell; David Streets; Zifeng Lu; Rex Britter; Steven R.H. Barrett; Carlo Ratti (352-363).
Air pollution related to traffic emissions pose an especially significant problem in cities; this is due to its adverse impact on human health and well-being. Previous studies which have aimed to quantify emissions from the transportation sector have been limited by either simulated or coarsely resolved traffic volume data. Emissions inventories form the basis of urban pollution models, therefore in this study, Global Positioning System (GPS) trajectory data from a taxi fleet of over 15,000 vehicles were analyzed with the aim of predicting air pollution emissions for Singapore. This novel approach enabled the quantification of instantaneous drive cycle parameters in high spatio-temporal resolution, which provided the basis for a microscopic emissions model. Carbon dioxide (CO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and particulate matter (PM) emissions were thus estimated. Highly localized areas of elevated emissions levels were identified, with a spatio-temporal precision not possible with previously used methods for estimating emissions. Relatively higher emissions areas were mainly concentrated in a few districts that were the Singapore Downtown Core area, to the north of the central urban region and to the east of it. Daily emissions quantified for the total motor vehicle population of Singapore were found to be comparable to another emissions dataset. Results demonstrated that high-resolution spatio-temporal vehicle traces detected using GPS in large taxi fleets could be used to infer highly localized areas of elevated acceleration and air pollution emissions in cities, and may become a complement to traditional emission estimates, especially in emerging cities and countries where reliable fine-grained urban air quality data is not easily available. This is the first study of its kind to investigate measured microscopic vehicle movement in tandem with microscopic emissions modeling for a substantial study domain.
Keywords: Air quality; Transportation; Emissions; Microscopic emissions model; Microscopic vehicle movement;

New directions: From biofuels to wood stoves: The modern and ancient air quality challenges in the megacity of São Paulo by Prashant Kumar; Maria de Fatima Andrade; Rita Yuri Ynoue; Adalgiza Fornaro; Edmilson Dias de Freitas; Jorge Martins; Leila D. Martins; Taciana Albuquerque; Yang Zhang; Lidia Morawska (364-369).
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The concentrations of polycyclic aromatic hydrocarbons (PAHs) have been determined in the gaseous phase and in various particulate matter (PM) size fractions at different locations in and outside of Stockholm, Sweden, representative of street level, urban and rural background. The focus has been on the seldom determined but highly carcinogenic dibenzopyrene isomers (DBPs) dibenzo[a,l]pyrene, dibenzo[a,e]pyrene, dibenzo[a,i]pyrene and dibenzo[a,h]pyrene. PAHs with 3 rings were found to be mainly associated with the vapor phase (>90%) whereas PAHs with 5–6 rings were mostly associated with particulate matter (>92%) and the 4-ringed PAHs partitioned between the two phases. PAH abundance was determined to be in the order street level > urban background > rural background with the PM10 street level 2010 mean of benzo[a]pyrene (B[a]P) reaching 0.24 ng/m3, well below the EU annual limit value of 1 ng/m3. In addition, higher PAH concentrations were found in the sub-micron particle fraction (PM1) as compared to the super-micron fraction (PM1-10) with the abundance in PM1 varying between 57 and 86% of the total PAHs.The B[a]P equivalent concentrations derived for DB[a,l]P and total DBPs exceeded 1–2 and 2–4 times, respectively, that of B[a]P at the four sampling sites; therefore underestimation of the cancer risk posed by PAHs in air could be made if the DBPs were not considered in risk assessment using the toxic equivalency approach, whilst the high correlation (p < 0.001) found in the relative concentrations supports the use of B[a]P as a marker substance for assessment of the carcinogenic risk associated to PAHs. However, the big difference in concentration ratios of B[a]P and the DBPs between the present study and some literature data calls for further research to evaluate the temporal and spatial invariance of the B[a]P/DBP ratios.
Keywords: Ambient air; Particulate matter; PAH; Benzo[a]pyrene; Benzo[a]pyrene equivalence; Dibenzo[a,l]pyrene; Toxicity;

Recent increase in Antarctic Peninsula ice core uranium concentrations by Mariusz Potocki; Paul A. Mayewski; Andrei V. Kurbatov; Jefferson C. Simões; Daniel A. Dixon; Ian Goodwin; Andrew M. Carleton; Michael J. Handley; Ricardo Jaña; Elena V. Korotkikh (381-385).
Understanding the distribution of airborne uranium is important because it can result in both chemical and radiological toxicity. Ice cores offer the most robust reconstruction of past atmospheric levels of toxic substances. Here we present the first sub-annually dated, continuously sampled ice core documenting change in U levels in the Southern Hemisphere. The ice core was recovered from the Detroit Plateau, northern Antarctic Peninsula, in 2007 by a joint Brazilian-Chilean-US team. It displays a significant increase in U concentration that coincides with reported mining activities in the Southern Hemisphere, notably Australia. Raw U concentrations in the Detroit Plateau ice core increased by as much as 102 between the 1980s and 2000s accompanied by increased variability in recent years. Decadal mean U concentrations increased by a factor of ∼3 from 1980 to 2007, reaching a mean of 205 pg/L from 2000 to 2007. The fact that other terrestrial source dust elements such as Ce, La, Pr, and Ti do not show a similar increase and that the increased U concentrations are enriched above natural crustal levels, supports an anthropogenic source for the U as opposed to a change in atmospheric circulation.
Keywords: Uranium; Pollution; Antarctic Peninsula; Antarctica;

Ozone (O3) and secondary organic aerosol (SOA) are important pollutants in the urban atmosphere. Benzene is one of the most important aromatic species in urban air, which could produce O3 and SOA in the presence of NOx (x = 1, 2) and UV light. A series of experiments was carried out to study the effect of particle water on O3 and SOA formation from benzene under various humid conditions in an indoor smog chamber. The results show that the peak O3 concentrations decreased with the increase of RH or the mass concentration of liquid NaCl particles. The peak O3 concentration reduced by 30% as RH increased from 9% to 87% with the similar initial concentrations of NaCl (about 46 μg m−3), and decreased by 10% as the initial NaCl concentrations increased from 36.0 μg m−3 to 152.1 μg m−3 at about 73% RH. The relationships between liquid water content (LWC) and O3 or SOA were investigated. The results show that LWC is the key factor that leads to an opposite effect on O3 and SOA formation from benzene. The peak O3 concentration exponentially decreased 37% as LWC0 increased from zero to 349.8 μg m−3. Heterogeneous reaction of dinitrogen pentoxide (N2O5) with particle water is the major reason for the decrease of O3. The yields of SOA increased from 5.2 to 10.5% as LWC0 increased from zero to 349.8 μg m−3. The relative intensities of bands O―H, C=O, C―OH and NO3 increased by 22.9, 6.8, 6.7 and 13.1 times respectively as compared with dry condition. Alcohols or hydrates are confirmed to be the major contributors to SOA with increasing LWC.
Keywords: Liquid water content; Ozone; Secondary organic aerosol; Aromatic; Smog chamber;

Anthropogenic non-methane volatile hydrocarbons at Mt. Cimone (2165 m a.s.l., Italy): Impact of sources and transport on atmospheric composition by Eleonora Lo Vullo; Francesco Furlani; Jgor Arduini; Umberto Giostra; Francesco Graziosi; Paolo Cristofanelli; Martin L. Williams; Michela Maione (395-403).
To advance our understanding of the factors that affect pollution in mountainous areas, long-term, high frequency measurements of thirteen Non Methane Volatile Organic Compounds (NMVOCs) have been carried out at the atmospheric observatory on the top of Mt. Cimone (2165 m a.s.l.), whose location is ideal for sampling both aged air masses representing the regional background and polluted air masses coming from nearby sources of anthropogenic pollution.An analysis of the NMVOC time series available at Mt. Cimone during 2010–2014 was used to examine the influence of transport processes on NMVOC atmospheric composition and to derive information on the emission sources. We performed a multifactor principal component analysis whose results allowed us to identify the source categories emitting the NMVOCs measured at Mt. Cimone as well as to assess transport ranges in winter and summer. Aged air masses, due to long-range transport and related to vehicular traffic exhaust emissions accounted for 78% of the NMVOC variability in winter and 62% in summer, whereas evaporative emissions, likely to be associated with fresh emissions from nearby sources, accounted for 12% of the NMVOC variability and 24% in winter and summer, respectively. Such results have been confirmed by a further analysis in which the NMVOC variability as a function of their atmospheric lifetimes has been evaluated. The ratios of alkane isomers potentially provides a metric to investigate seasonal changes in NMVOCs composition and in the emission fields of butanes and pentanes, suggesting that during the summer the butanes are originating mainly from the European domain and that for pentanes non-anthropogenic sources may be contributing to the measured concentrations.
Keywords: Volatile organic compounds; Anthropogenic emissions; Emission patterns; Photochemical oxidation; Principal component analysis;

Taiyuan city in Shanxi province, China has been one of the top heavily polluted cities in the world for a long time with large industrial emissions and high disease burden. Many pollution control strategies have been implemented forcefully by the government in recent years in Taiyuan. To better understand the effect of the strategies and related influence factors, we studied polycyclic aromatic hydrocarbons (PAHs) in fine particulate matter (PM2.5) during heating seasons in Taiyuan from 2009 to 2013. The results showed that the concentrations of PM2.5 (70.7–477.9 μg/m3) and related total PAHs (T-PAHs, 128.7–1840.2 ng/m3) far exceeded the air quality standards issued by the Ministry of Environmental Protection of China (MEP) and were higher than those in many domestic and foreign cities in spite of the pollution control. Source apportionment by the diagnostic ratio analysis and PMF model found that coal consumption contributed the most (52.1%) to the total PM2.5-bound PAHs followed by the coking industry (27.3%) and traffic exhausts (20.6%). Significant decreases in PM2.5 and PAHs levels were found in 2013, which was probably due to the large abatement of residential coal consumption and favorable meteorological factors. Being located in the north of Taiyuan basin, the pollution in Taiyuan could be aggravated by the regional transport of coal combustion- and coking-related pollutants from other industrial development zones in the south-western basin as found by the analysis of meteorological influence and back trajectory. Although the PAHs were the lowest in 2013, the BaPeq or ILCR were the highest in that year. This should be related to the increasing vehicle numbers in Taiyuan, because vehicle exhaust tends to enrich in higher molecular weight and more toxic PAHs. Our results provided useful guidance for solving the air pollution problem for cities in a semi- or total-closed basin with coal as the major energy source such as Taiyuan.
Keywords: Fine particulate matter (PM2.5); Polycyclic aromatic hydrocarbons (PAHs); Heating season; Pollution control; Positive matrix factorization (PMF);

Effects of different temperature treatments on biological ice nuclei in snow samples by Kazutaka Hara; Teruya Maki; Makiko Kakikawa; Fumihisa Kobayashi; Atsushi Matsuki (415-419).
The heat tolerance of biological ice nucleation activity (INA) depends on their types. Different temperature treatments may cause varying degrees of inactivation on biological ice nuclei (IN) in precipitation samples. In this study, we measured IN concentration and bacterial INA in snow samples using a drop freezing assay, and compared the results for unheated snow and snow treated at 40 °C and 90 °C. At a measured temperature of −7 °C, the concentration of IN in untreated snow was 100–570 L−1, whereas the concentration in snow treated at 40 °C and 90 °C was 31–270 L−1 and 2.5–14 L−1, respectively. In the present study, heat sensitive IN inactivated by heating at 40 °C were predominant, and ranged 23–78% of IN at −7 °C compared with untreated samples. Ice nucleation active Pseudomonas strains were also isolated from the snow samples, and heating at 40 °C and 90 °C inactivated these microorganisms. Consequently, different temperature treatments induced varying degrees of inactivation on IN in snow samples. Differences in the concentration of IN across a range of treatment temperatures might reflect the abundance of different heat sensitive biological IN components.
Keywords: Heat sensitive ice nuclei; Ice nucleation active bacteria; Drop freezing assay; Bioaerosols;

The optimal regression equations for the dust emission flux parameterized with the friction velocity (u*) only, the friction velocity with the threshold friction velocity (u*t) and the friction velocity together with the flux Richardson number (Rf) in the dust source region are derived using the sonic anemometer measured momentum and kinematic heat fluxes at 8 m height and the two-level (3 m and 15 m height) measured PM10 concentrations from a 20-m monitoring tower located at Naiman in the Asian dust source region in China for the period from March 2013 to November 2014. The analysis period is divided into three sub-periods based on the Normalized Difference Vegetation Index (NDVI) to eliminate the effect of vegetation on the dust emission flux. The dust event is identified as a peak half hourly mean dust concentration (PM10) at 3 m height exceeding the sub-period mean dust concentration plus one standard deviation of the sub-period. The total of 317 dust events is identified with the highest number of dust event of 18.8 times a month in summer. The optimal regression equations of the dust emission flux (Fc) for dust events parameterized with u* and Rf are found to simulate quite well the dust emission flux estimated by the observed data at the site for all periods especially for the unstable stratification, suggesting the potential usefulness of these equations parameterized by u* with Rf rather than those by u* only and u* together with u*t for the estimation of the dust emission flux in the Asian dust source region.Display Omitted
Keywords: Asian dust monitoring tower; Convective velocity; Dust emission flux; Flux Richardson number; Gradient method; Naiman; Optimal regression equation;

Assessment of microscale spatio-temporal variation of air pollution at an urban hotspot in Madrid (Spain) through an extensive field campaign by Rafael Borge; Adolfo Narros; Begoña Artíñano; Carlos Yagüe; Francisco Javier Gómez-Moreno; David de la Paz; Carlos Román-Cascón; Elías Díaz; Gregorio Maqueda; Mariano Sastre; Christina Quaassdorff; Chrysanthi Dimitroulopoulou; Sotiris Vardoulakis (432-445).
Poor urban air quality is one of the main environmental concerns worldwide due to its implications for population exposure and health-related issues. However, the development of effective abatement strategies in cities requires a consistent and holistic assessment of air pollution processes, taking into account all the relevant scales within a city. This contribution presents the methodology and main results of an intensive experimental campaign carried out in a complex pollution hotspot in Madrid (Spain) under the TECNAIRE-CM research project, which aimed at understanding the microscale spatio-temporal variation of ambient concentration levels in areas where high pollution values are recorded. A variety of instruments were deployed during a three-week field campaign to provide detailed information on meteorological and micrometeorological parameters and spatio-temporal variations of the most relevant pollutants (NO2 and PM) along with relevant information needed to simulate pedestrian fluxes. The results show the strong dependence of ambient concentrations on local emissions and meteorology that turns out in strong spatial and temporal variations, with gradients up to 2 μg m−3 m−1 for NO2 and 55 μg m−3 min−1 for PM10. Pedestrian exposure to these pollutants also presents strong variations temporally and spatially but it concentrates on pedestrian crossings and bus stops. The analysis of the results show that the high concentration levels found in urban hotspots depend on extremely complex dynamic processes that cannot be captured by routinely measurements made by air quality monitoring stations used for regulatory compliance assessment. The large influence from local traffic in the concentration fields highlights the need for a detailed description of specific variables that determine emissions and dispersion at microscale level. This also indicates that city-scale interventions may be complemented with local control measures and exposure management, to improve air quality and reduce air pollution health effects more effectively.Display Omitted
Keywords: Air quality; Urban hotspot; Experimental campaign; Microscale; Exposure; Madrid; TECNAIRE-CM;

Changes in US background ozone due to global anthropogenic emissions from 1970 to 2020 by Uarporn Nopmongcol; Jaegun Jung; Naresh Kumar; Greg Yarwood (446-455).
Estimates of North American and US Background (NAB and USB) ozone (O3) are critical in setting and implementing the US National Ambient Air Quality Standards (NAAQS) and therefore influence population exposure to O3 across the US. NAB is defined as the O3 concentration in the absence of anthropogenic O3 precursor emissions from North America whereas USB excludes anthropogenic emissions inside the US alone. NAB and USB vary geographically and with time of year. Analyses of O3 trends at rural locations near the west coast suggest that background O3 is rising in response to increasing non-US emissions. As the O3 NAAQS is lowered, rising background O3 would make attaining the NAAQS more difficult. Most studies of changing US background O3 have inferred trends from observations whereas air quality management decisions tend to rely on models. Thus, it is important that the models used to develop O3 management strategies are able to represent the changes in background O3 in order to increase confidence that air quality management strategies will succeed. We focus on how changing global emissions influence USB rather than the effects of inter-annual meteorological variation or long-term climate change. We use a regional model (CAMx) nested within a global model (GEOS-Chem) to refine our grid resolution over high terrain in the western US and near US borders where USB tends to be higher. We determine USB from CAMx simulations that exclude US anthropogenic emissions. Over five decades, from 1970 to 2020, estimated USB for the annual fourth highest maximum daily 8-h average O3 (H4MDA8) in the western US increased from mostly in the range of 40–55 ppb to 45–60 ppb, but remained below 45 ppb in the eastern US. USB increases in the southwestern US are consistent with rising emissions in Asia and Mexico. USB decreases in the northeast US after 1990 follow declining Canadian emissions. Our results show that the USB increases both for the top 30 MDA8 days and the H4MDA8 (the former at a faster rate in most areas). Our USB increases in the western US are lower by about a factor of four than trends inferred from analyses of rural ozone near the west coast which is consistent with meteorology also influencing the observed ozone trends. Comparing H4MDA8 NAB and USB for 2020 shows that contributions from neighbouring countries can exceed 4 ppb near the Canadian border and 2 ppb near the Mexican border.
Keywords: Ozone; Photochemical modeling; NAB; USB; Non-US emissions; US ozone standard; Background ozone;

Predicting sulphur and nitrogen deposition using a simple statistical method by Filip Oulehle; Jiří Kopáček; Tomáš Chuman; Vladimír Černohous; Iva Hůnová; Jakub Hruška; Pavel Krám; Zora Lachmanová; Tomáš Navrátil; Petr Štěpánek; Miroslav Tesař; Christopher D. Evans (456-468).
Data from 32 long-term (1994–2012) monitoring sites were used to assess temporal development and spatial variability of sulphur (S) and inorganic nitrogen (N) concentrations in bulk precipitation, and S in throughfall, for the Czech Republic. Despite large variance in absolute S and N concentration/deposition among sites, temporal coherence using standardised data (Z score) was demonstrated. Overall significant declines of SO4 concentration in bulk and throughfall precipitation, as well as NO3 and NH4 concentration in bulk precipitation, were observed. Median Z score values of bulk SO4, NO3 and NH4 and throughfall SO4 derived from observations and the respective emission rates of SO2, NOx and NH3 in the Czech Republic and Slovakia showed highly significant (p < 0.001) relationships. Using linear regression models, Z score values were calculated for the whole period 1900–2012 and then back-transformed to give estimates of concentration for the individual sites. Uncertainty associated with the concentration calculations was estimated as 20% for SO4 bulk precipitation, 22% for throughfall SO4, 18% for bulk NO3 and 28% for bulk NH4. The application of the method suggested that it is effective in the long-term reconstruction and prediction of S and N deposition at a variety of sites. Multiple regression modelling was used to extrapolate site characteristics (mean precipitation chemistry and its standard deviation) from monitored to unmonitored sites. Spatially distributed temporal development of S and N depositions were calculated since 1900. The method allows spatio-temporal estimation of the acid deposition in regions with extensive monitoring of precipitation chemistry.Display Omitted
Keywords: Precipitation; Sulphur; Nitrogen; Deposition; Monitoring; Upscaling;

Determination of the bioaccessible fraction of metals in urban aerosol using simulated lung fluids by Pavel Coufalík; Pavel Mikuška; Tomáš Matoušek; Zbyněk Večeřa (469-475).
Determination of the bioaccessible fraction of metals in atmospheric aerosol is a significant issue with respect to air pollution in the urban environment. The aim of this work was to compare of metal bioaccessibility determined according to the extraction yields of six simulated lung fluids. Aerosol samples of the PM1 fraction were collected in Brno, Czech Republic. The total contents of Cd, Ce, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn in the samples were determined and their enrichment factors were calculated. The bioaccessible proportions of elements were determined by means of extraction in Gamble’s solution, Gamble’s solution with dipalmitoyl phosphatidyl choline (DPPC), artificial lysosomal fluid, saline, water, and in a newly proposed solution based on DPPC, referred to as “Simulated Alveoli Fluid” (SAF). The chemical composition and surface tension of the simulated lung fluids were the main parameters influencing extraction yields. Gamble’s solutions and the newly designed solution of SAF exhibited the lowest extraction efficiency, and also had the lowest surface tensions. The bioaccessibility of particulate metals should be assessed by synthetic lung fluids with a low surface tension, which simulate better the behavior and composition of native lung surfactant. The bioaccessibility of metals in aerosol assessed by means of the extraction in water or artificial lysosomal fluid can be overestimated.
Keywords: Metal; Aerosol; Simulated lung fluid; Surface tension;

Lately released particular matter (PM) and gaseous pollutants (SO2, NO2, CO, and O3) data observed in three mega cities (Beijing, Shanghai, and Guangzhou) over China from April 2014 to March 2015 are employed to analyze the current situation of air pollutions. Meteorological data during the same time period are also used to explain the variations of air pollutants. Annual averaged PM2.5 and PM10 mass concentrations shows that the highest magnitude and strongest seasonal variations occurring in Beijing and lowest magnitude and weakest seasonal variations in Guangzhou. During the study period, 37%, 21% and 7% of the PM2.5, and 20%, 6% and 1% of the PM10 mass concentration exceeded the National Ambient Air Quality Standard (NAAQS) Grade II. Large differences in the ratios of PM2.5 to PM10 between the episode and non-episodes days are found in Beijing (0.22), which is almost twice as in Shanghai (0.12) due to less episode days in the latter. Compared to Beijing and Shanghai, no episode days were found in spring and summer in Guangzhou, the episode days occur only from mid-fall to winter. NO2 concentrations shows a marked increase during the late fall to wintertime over all three cities, which is consistent with the seasonal variations of PM concentrations. SO2 concentrations show a slight increase during the wintertime and CO also shows an increase in winter due to emissions by vehicle cold start. SO2 and CO concentrations during the study period are below the Grade-II standards but NO2 concentrations exceed the Grade-II standards from late to winter. Compared to the concentrations of decade ago, SO2 decreases around 70%, NO2 decreases around 25%, and CO decreases around 45%. O3 shows a strong seasonal variation, with relatively high magnitude in summer and low in winter, which is quite distinct from the seasonal variations of other gases pollutant and PM pollutions. The impact of meteorological conditions, such as precipitation, wind speed, relative humidity, and temperature, on PM and gaseous concentrations are also examined.
Keywords: PM2.5; PM10; Gaseous pollutants; China; Megacities;

Black carbon and fine particle emissions in Finnish residential wood combustion: Emission projections, reduction measures and the impact of combustion practices by Mikko Savolahti; Niko Karvosenoja; Jarkko Tissari; Kaarle Kupiainen; Olli Sippula; Jorma Jokiniemi (495-505).
Residential wood combustion (RWC) is a major source of black carbon (BC) and PM2.5 emissions in Finland. Making a robust assessment of emissions on a national level is a challenge due to the varying heater technologies and the effect of users’ combustion practices. In this paper we present an update of the emission calculation scheme for Finnish RWC, including technology-specific emission factors based on national measurements. Furthermore, we introduce a transparent method to assess the impact of poor combustion practices on emissions. Using a Finnish emission model, we assessed the emissions in 2000, 2010 and 2030, as well as the cost-efficiency of potential emission reduction measures. The results show that RWC is the biggest source of both PM2.5 and BC emissions in Finland, accounting for 37% and 55% of the total respective emissions. It will also remain the biggest source in the future, and it’s role may become even more pronounced if wood consumption continues to increase. Sauna stoves cause the most emissions and also show the biggest potential for emission reductions. Informational campaigns targeted to improve heater users’ combustion practices appear as a highly cost-efficient measure, although their impact on country-level emissions was estimated to be relatively limited.
Keywords: Black carbon; PM2.5; Residential wood combustion; Emission; Reduction measure;

Microbial activities in the atmosphere can indicate the physiological processes of microorganisms and can indirectly affect cloud formation and environmental health. In this study, the microbial activity in bioaerosols collected in the Qingdao coastal region was investigated using the fluorescein diacetate (FDA) hydrolysis method to detect the enzyme activity of microorganisms. The results showed that the microbial activity ranged from 5.49 to 102 ng/m3 sodium fluorescein from March 2013 to February 2014; the average value was 34.4 ng/m3. Microbial activity has no statistical correlation with total microbial quantity. Multiple linear regression analysis showed that meteorological factors such as atmospheric temperature, relative humidity and wind speed accounted for approximately 35.7% of the variation of the microbial activity, although their individual impacts on microbial activity varied. According to the correlation analysis, atmospheric temperature and wind speed had a significant positive and negative influence on microbial activity, respectively, whereas relative humidity and wind direction had no significant influence. The seasonal distribution of microbial activity in bioaerosols was in the order of summer > autumn > winter > spring, with high fluctuations in the summer and autumn. Microbial activity in bioaerosols differed in different weather conditions such as the sunny, foggy, and hazy days of different seasons. Further in situ observations in different weather conditions at different times and places are needed to understand the seasonal distribution characteristics of microbial activity in bioaerosols and the influence factors of microbial activity.
Keywords: Bioaerosols; Microbial activity; Total microbe; Seasonal distribution; Meteorological factors;

The suitability of Red Pine trees (Pinus Resinosa) to act as passive samplers for persistent organic pollutants (POPs) in outdoor air and to provide historic information on air concentration trends was demonstrated in this preliminary investigation. Red Pine tree cores from Toronto, Canada, were tested for polycyclic aromatic hydrocarbon (PAHs), alkylated-PAHs, nitro and oxy-PAHs, polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (novel BFRs). The PBDEs and novel BFRs demonstrated a similar relative contribution in cores representing 30 years of tree growth, to that reported in contemporary air samples. Analysis of tree ring segments of 5–15 years resulted in detectable concentrations of some PAHs and alk-PAHs and demonstrated a transition from petrogenic sources to pyrogenic sources over the period 1960–2015. A simple uptake model was developed that treats the tree rings as linear-phase passive air samplers. The bark infiltration factor, IFBARK, is a key parameter of the model that reflects the permeability of the bark to allow chemicals to be transferred from ambient air to the outer tree layer (cambium). An IFBARK of about 2% was derived for the Red Pine trees based on tree core and air monitoring data.
Keywords: Tree cores; POPs; PAHs; BFRs; Historic trends;

Ultrafine particles (diameter <100 nm) are of great topical interest because of concerns over possible enhanced toxicity relative to larger particles of the same composition. While combustion processes, and especially road traffic exhaust are a known major source of ultrafine particle emissions, relatively little is known of the magnitude of emissions from non-traffic sources. One such source is the incineration of municipal waste, and this article reviews studies carried out on the emissions from modern municipal waste incinerators. The effects of engineering controls upon particle emissions are considered, as well as the very limited information on the effects of changing waste composition. The results of measurements of incinerator flue gas, and of atmospheric sampling at ground level in the vicinity of incinerators, show that typical ultrafine particle concentrations in flue gas are broadly similar to those in urban air and that consequently, after the dispersion process dilutes incinerator exhaust with ambient air, ultrafine particle concentrations are typically indistinguishable from those that would occur in the absence of the incinerator. In some cases the ultrafine particle concentration in the flue gas may be below that in the local ambient air. This appears to be a consequence of the removal of semi-volatile vapours in the secondary combustion zone and abatement plant, and the high efficiency of fabric filters for ultrafine particle collection.
Keywords: Ultrafine particles; Nanoparticles; Particle removal devices; Incinerator emissions;

Development and evaluation of a daily temporal interpolation model for fine particulate matter species concentrations and source apportionment by Jeremiah D. Redman; Heather A. Holmes; Sivaraman Balachandran; Marissa L. Maier; Xinxin Zhai; Cesunica Ivey; Kyle Digby; James A. Mulholland; Armistead G. Russell (529-538).
The impacts of emissions sources on air quality in St. Louis, Missouri are assessed for use in acute health effects studies. However, like many locations in the United States, the speciated particulate matter (PM) measurements from regulatory monitoring networks in St. Louis are only available every third day. The power of studies investigating acute health effects of air pollution is reduced when using one-in-three day source impacts compared to daily source impacts. This paper presents a temporal interpolation model to estimate daily speciated PM2.5 mass concentrations and source impact estimates using one-in-three day measurements. The model is used to interpolate 1-in-3 day source impact estimates and to interpolate the 1-in-3 day PM species concentrations prior to source apportionment (SA). Both approaches are compared and evaluated using two years (June 2001–May 2003) of daily data from the St. Louis Midwest Supersite (STL-SS). Data withholding is used to simulate a 1-in-3 day data set from the daily data to evaluate interpolated estimates. After evaluation using the STL-SS data, the model is used to estimate daily source impacts at another site approximately seven kilometers (7 km) northwest of the STL-SS (Blair); results between the sites are compared. For interpolated species concentrations, the model performs better for secondary species (sulfate, nitrate, ammonium, and organic carbon) than for primary species (metals and elemental carbon), likely due to the greater spatial autocorrelation of secondary species. Pearson correlation (R) values for sulfate, nitrate, ammonium, elemental carbon, and organic carbon ranged from 0.61 (elemental carbon, EC2) to 0.97 (sulfate). For trace metals, the R values ranged from 0.31 (Ba) to 0.81 (K). The interpolated source impact estimates also indicated a stronger correlation for secondary sources. Correlations of the secondary source impact estimates based on measurement data and interpolation data ranged from 0.68 to 0.97, whereas for primary source contribution estimates the correlations ranged from −0.042 to 0.95. Comparison of daily source impact estimates with source impacts from the interpolation models indicated that interpolation of source contributions was preferable over interpolating species concentrations then applying a SA model. This was based on better agreement in the predicted source impact concentrations and higher correlation with daily SA results. Overall, this study indicates that the temporal interpolation model produces results that may be used to estimate source impacts for health studies, though the additional uncertainty should be considered.
Keywords: Chemical mass balance; Positive matrix factorization; Chemical speciation network; Source impact estimates; Air quality; St. Louis;

Contribution of regional-scale fire events to ozone and PM2.5 air quality estimated by photochemical modeling approaches by K.R. Baker; M.C. Woody; G.S. Tonnesen; W. Hutzell; H.O.T. Pye; M.R. Beaver; G. Pouliot; T. Pierce (539-554).
Two specific fires from 2011 are tracked for local to regional scale contribution to ozone (O3) and fine particulate matter (PM2.5) using a freely available regulatory modeling system that includes the BlueSky wildland fire emissions tool, Spare Matrix Operator Kernel Emissions (SMOKE) model, Weather and Research Forecasting (WRF) meteorological model, and Community Multiscale Air Quality (CMAQ) photochemical grid model. The modeling system was applied to track the contribution from a wildfire (Wallow) and prescribed fire (Flint Hills) using both source sensitivity and source apportionment approaches. The model estimated fire contribution to primary and secondary pollutants are comparable using source sensitivity (brute-force zero out) and source apportionment (Integrated Source Apportionment Method) approaches. Model estimated O3 enhancement relative to CO is similar to values reported in literature indicating the modeling system captures the range of O3 inhibition possible near fires and O3 production both near the fire and downwind. O3 and peroxyacetyl nitrate (PAN) are formed in the fire plume and transported downwind along with highly reactive VOC species such as formaldehyde and acetaldehyde that are both emitted by the fire and rapidly produced in the fire plume by VOC oxidation reactions. PAN and aldehydes contribute to continued downwind O3 production. The transport and thermal decomposition of PAN to nitrogen oxides (NOX) enables O3 production in areas limited by NOX availability and the photolysis of aldehydes to produce free radicals (HOX) causes increased O3 production in NOX rich areas. The modeling system tends to overestimate hourly surface O3 at routine rural monitors in close proximity to the fires when the model predicts elevated fire impacts on O3 and Hazard Mapping System (HMS) data indicates possible fire impact. A sensitivity simulation in which solar radiation and photolysis rates were more aggressively attenuated by aerosol in the plume reduced model O3 but does not eliminate this bias. A comparison of model predicted daily average speciated PM2.5 at surface rural routine network sites when the model predicts fire impacts from either of these fires shows a tendency toward overestimation of PM2.5 organic aerosol in close proximity to these fires. The standard version of the CMAQ treats primarily emitted organic aerosol as non-volatile. An alternative approach for treating organic aerosol as semi-volatile resulted in lower PM2.5 organic aerosol from these fires but does not eliminate the bias. Future work should focus on modeling specific fire events that are well characterized in terms of size, emissions, and have extensive measurements taken near the fire and downwind to better constrain model representation of important physical and chemical processes (e.g. aerosol photolysis attenuation and organic aerosol treatment) related to wild and prescribed fires.
Keywords: Wild fire; Prescribed fire; Photochemical model; Ozone; Particulate matter;

Assessing the contribution of water to the mass closure of PM10 by C. Perrino; M. Catrambone; C. Farao; S. Canepari (555-564).
The data obtained during a number of field studies aimed at determining the chemical composition of atmospheric particulate matter (PM) have shown that the measurement of the main PM components (main elements, ions, elemental carbon, organic carbon) was generally sufficient to obtain a reasonable mass closure. Notwithstanding, a wide gap between PM mass concentration and reconstructed mass was observed in two peculiar environmental conditions: desert dust intrusion and severe atmospheric stability episodes characterized by very high ammonium nitrate concentration. In these two cases, the mass closure improved significantly by adding the concentration of PM–bound water. Water was determined by using a coulometric Karl–Fisher system equipped with a controlled heating device; the method was able to separate different water contributions released in different temperature ranges from 50 to 250 °C.In our field studies the amount of water associated to ammonium salts in winter stability conditions was mostly dependent on ammonium nitrate concentration and constituted up to 22% of the total PM10 mass; the specific water contribution linked to ammonium salts (released in the temperature range 180–250 °C) constituted up to 30% of the ammonium nitrate mass. It was confirmed that in these extreme conditions quartz and Teflon filters behave differently: when measured on quartz filters, PM concentration was lower than on Teflon, the mass closure was satisfactory and the concentration of water was presumably very low.In the case of desert dust episodes, water was up to 10% of total PM10 mass; the specific water contribution linked to desert dust (released in the temperature range 100–180 °C) constituted about 5% of the mass of soil components. In other environmental situations, such as urban environments, marine atmosphere and rural areas, the concentration of PM–bound water was below 2–3 μg/m3.
Keywords: PM–bound water; Atmospheric stability; Desert dust; Ammonium nitrate; PM macro-sources;

Organic matter is the most complicated and unresolved major component of atmospheric aerosol particles. Its sources and global budget are still highly uncertain and thereby necessitate further research efforts with state-of-the-art instrument. This study employed a Thermo-Desorption Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (TD-PTR-TOF-MS) for characterization of ambient organic aerosols. First, five authentic standard substances, which include phthalic acid, levoglucosan, arabitol, cis-pinonic acid and glutaric acid, were utilized to examine the response of the instrument. The results demonstrated the linearity of the TD-PTR-TOF-MS signals against a range of mass loading of specific species on filters. However, it was found that significant fragmentation happened to those challenging compounds, although the proton-transfer-reaction (PTR) was recognized as a soft ionization technique. Consequently, quantitative characterization of aerosols with the TD-PTR-TOF-MS depended on the availability of the fragmentation pattern in mass spectra and the recovery rate with the quantification ion peak(s). The instrument was further deployed to analyze a subset of submicron aerosol samples collected at the TARO (Taipei Aerosol and Radiation Observatory) in Taipei, Taiwan during August 2013. The results were compared with the measurements from a conventional DRI thermo-optical carbon analyzer. The inter-comparison indicated that the TD-PTR-TOF-MS underestimated the mass of total organic matter (TOM) in aerosol samples by 27%. The underestimation was most likely due to the thermo-decomposition during desorption processes and fragmentation in PTR drift tube, where undetectable fragments were formed. Besides, condensation loss of low vapor pressure species in the transfer components was also responsible for the underestimation to a certain degree. Nevertheless, it was showed that the sum of the mass concentrations of the major detected ion peaks correlated strongly with the TOM determined by DRI analyzer (R2 = 0.8578), suggesting that the TD-PTR-TOF-MS measurements explained more than 85% of the variance in the time series of TOM. In addition to identification by comparing with the fragmentation pattern obtained from the mass spectra of the authentic substances, most of the major ions were attributed to protonated or acylium ions of specific parent compounds. Amongst the quantified species with full calibration with authentic standard, phthalic acid was found accounting for 7.0% of the mass loading of TOM. In addition, a high-end estimation of 9.4% was suggested for the mass contribution from glutaric acid, which was made by assuming that the ion with m/z of 73.027 was totally produced from fragmentation of glutaric acid as characterization of authentic standard despite of the formation of protonated methyl-glyoxal ion. Moreover, a substantial contribution from ions corresponding to protonated acetic acid and acetone was measured, which could be produced from fragmentation of larger oxygenated molecules. The TD-PTR-TOF-MS measurements suggested that low molecular weight carboxylic acid (LMWCA), products of photochemical oxidation of gaseous hydrocarbons and fatty acids, constituted a major fraction of secondary organic aerosols in Taipei, Taiwan, a typical subtropical urban area.Display Omitted
Keywords: Atmospheric aerosols; Organic tracers; Low molecular weight carboxylic acids (LMWCA); Proton-Transfer-Reaction Mass Spectrometer (PTRMS);

Exploring synergies between climate and air quality policies using long-term global and regional emission scenarios by Olivia Braspenning Radu; Maarten van den Berg; Zbigniew Klimont; Sebastiaan Deetman; Greet Janssens-Maenhout; Marilena Muntean; Chris Heyes; Frank Dentener; Detlef P. van Vuuren (577-591).
In this paper, we present ten scenarios developed using the IMAGE2.4 framework (Integrated Model to Assess the Global Environment) to explore how different assumptions on future climate and air pollution policies influence emissions of greenhouse gases and air pollutants. These scenarios describe emission developments in 26 world regions for the 21st century, using a matrix of climate and air pollution policies. For climate policy, the study uses a baseline resulting in forcing levels slightly above RCP6.0 and an ambitious climate policy scenario similar to RCP2.6. For air pollution, the study explores increasingly tight emission standards, ranging from no improvement, current legislation and three variants assuming further improvements. For all pollutants, the results show that more stringent control policies are needed after 2030 to prevent a rise in emissions due to increased activities and further reduce emissions. The results also show that climate mitigation policies have the highest impact on SO2 and NOX emissions, while their impact on BC and OC emissions is relatively low, determined by the overlap between greenhouse gas and air pollutant emission sources. Climate policy can have important co-benefits; a 10% decrease in global CO2 emissions by 2100 leads to a decrease of SO2 and NOX emissions by about 10% and 5%, respectively compared to 2005 levels. In most regions, low levels of air pollutant emissions can also be achieved by solely implementing stringent air pollution policies. The largest differences across the scenarios are found in Asia and other developing regions, where a combination of climate and air pollution policy is needed to bring air pollution levels below those of today.
Keywords: Climate policy; Air pollution policy; Scenarios; Co-benefits; Representative concentration pathways;

Long-range transport of Saharan dust and chemical transformations over the Eastern Mediterranean by E. Athanasopoulou; A. Protonotariou; G. Papangelis; M. Tombrou; N. Mihalopoulos; E. Gerasopoulos (592-604).
Three recent Saharan dust outbreaks during different seasons (4–6 days in winter of 2009, late autumn of 2010 and summer of 2011) are selected in order to study the chemical footprint and aging processes of dust intrusions over the Eastern Mediterranean (EM). The applied model system (PMCAMx, WRF and GEOS-CHEM) and methodology are found competent to reproduce dust production, long-range transport and chemical transformations over the EM, with the synergistic use of synoptic patterns analysis, optical depth retrievals, back-trajectories, surface and satellite aerosol measurements. The dust loads were high during the cold period events and much lighter during summertime, when transport was mainly in the free troposphere. In all cases, dust originated from the northwest and/or west Saharan desert and reached the EM from the west/southwest. Sensitivity runs underlie the effect of dust transport on the chemical constituents of aerosols over the EM and show a large impact on calcium (70–90% of maximum daily values 2–5 μg m−3), with its gradient at surface level being around −10% per 100 km along the dust pathway. For the cold period cases, this value can also be considered analogous to the dust dissipation ratio, because the plume is vertically extended down to the surface layers. Interestingly, the surface particulate nitrate concentrations over the EM are reversely affected by the approaching dust loads, exhibiting the highest values (up to 6 μg m−3) and the largest dust fraction (ca. 70%) during summertime. This is attributed to the enhanced nitric acid formation under high atmospheric temperature and insolation, its uptake onto the carbonate dust particles, and their effective accumulation, due to low deposition rates over the sea and scarce precipitation. Sulfate formation onto dust particles is found insignificant (rapid reaction with ammonia and/or sea-salt), while the influence of dust and sea-salt on sodium, when spatio-temporal averages are calculated, is approximately equal.
Keywords: Saharan dust events; Eastern Mediterranean (EM); Aerosol modeling; Chemical impacts of dust; Dust-bound nitrate;

Research on aerosol profiles and parameterization scheme in Southeast China by Gang Wang; Tao Deng; Haobo Tan; Xiantong Liu; Honglong Yang (605-613).
The vertical distribution of the aerosol extinction coefficient serves as a basis for evaluating aerosol radiative forcing and air quality modeling. In this study, MODIS AOD data and ground-based lidar extinction coefficients were employed to verify 6 years (2009–2014) aerosol extinction data obtained via CALIOP for Southeast China. The objective was mainly to provide the parameterization scheme of annual and seasonal aerosol extinction profiles. The results showed that the horizontal and vertical distributions of CALIOP extinction data were highly accurate in Southeast China. The annual average AOD below 2 km accounted for 64% of the total layer, with larger proportions observed in winter (80%) and autumn (80%) and lower proportions observed in summer (70%) and spring (59%). The AOD was maximum in the spring (0.58), followed by the autumn and winter (0.44), and reached a minimum in the summer (0.40). The near-surface extinction coefficient increased from summer, spring, autumn and winter, in that order. The Elterman profile is obviously lower than the profiles observed by CALIOP in Southeast China. The annual average and seasonal aerosol profiles showed an exponential distribution, and could be divided into two sections. Two sections exponential fitting was used in the parameterization scheme. In the first section, the aerosol scale height reached 2200 m with a maximum (3,500 m) in summer and a minimum (1,230 m) in winter, which meant that the aerosol extinction decrease with height slower in summer, but more rapidly in winter. In second section, the aerosol scale height was maximum in spring, which meant that the higher aerosol diffused in spring.
Keywords: CALIOP; Aerosol profiles; Extinction coefficient; Parameterization scheme; Southeast China;

A survey of jet aircraft PM by TEM in APEX III by Chung-Hsuan Huang; Victoria M. Bryg; Randy L. Vander Wal (614-622).
Results are reported for sampling non-volatile particulate matter from field tests during the NASA led APEX III campaign. This paper reports observations of particulate emissions collected from a suite of jet engine aircraft to assess differences and similarities in soot macro- micro- and nanostructure using TEM. Aggregates are compact, primary particle sizes varied and nanostructure is mixed. Comparisons are made to soot from a laboratory flame as a well-studied reference. Results are interpreted in terms of turbulence interacting with the different stages of particle formation and growth with implications for atmospheric processing and climate impact.Display Omitted
Keywords: Soot; Nanostructure; APEX III; Aggregate morphology; Microstructure; HRTEM;

Chemistry characterization of jet aircraft engine particulate matter by XPS: Results from APEX III by Randy L. Vander Wal; Victoria M. Bryg; Chung-Hsuan Huang (623-629).
This paper reports X-ray photoelectron spectroscopy (XPS) analysis of jet exhaust particulate matter (PM) from a B737, Lear, ERJ and A300 aircraft during the APEX III NASA led field campaign. Carbon hybridization and bonding chemistry are identified by high-resolution scans about the C1s core-shell region. Significant organic content as gauged by the sp3/sp2 ratio is found across engines and powers. Polar oxygen functional groups include carboxylic, carbonyl and phenol with combined content of 20% or more. By survey scans various elements including transition metals are identified along with lighter elements such as S, N and O in the form of oxides. Additives within lubricants are probable sources of Na, Ba, Ca, Zn, P and possibly Sn. Elements present and their percentages varied significantly across all engines, not revealing any trend or identifiable cause for the differences, though the origin is likely the same for the same element when observed. This finding suggests that their collective presence could serve as an environmental tracer for identifying PM originating from aircraft engines and serving as a diagnostic for engine performance and wear.Display Omitted
Keywords: XPS; APEX III; Particulate matter (PM); Soot; Surface chemistry;