Atmospheric Environment (v.141, #C)

2014 iAREA campaign on aerosol in Spitsbergen – Part 2: Optical properties from Raman-lidar and in-situ observations at Ny-Ålesund by C. Ritter; R. Neuber; Alexander Schulz; K.M. Markowicz; I.S. Stachlewska; J. Lisok; P. Makuch; P. Pakszys; P. Markuszewski; A. Rozwadowska; T. Petelski; T. Zielinski; S. Becagli; R. Traversi; R. Udisti; M. Gausa (1-19).
In this work multi wavelength Raman lidar data from Ny-Ålesund, Spitsbergen have been analysed for the spring 2014 Arctic haze season, as part of the iAREA campaign. Typical values and probability distributions for aerosol backscatter, extinction and depolarisation, the lidar ratio and the color ratio for 4 different altitude intervals within the troposphere are given. These quantities and their dependencies are analysed and the frequency of altitude-dependent observed aerosol events are given. A comparison with ground-based size distribution and chemical composition is performed. Hence the aim of this paper is to provide typical and statistically meaningful properties of Arctic aerosol, which may be used in climate models or to constrain the radiative forcing. We have found that the 2014 season was only moderately polluted with Arctic haze and that sea salt and sulphate were the most dominant aerosol species. Moreover the drying of an aerosol layer after cloud disintegration has been observed. Hardly any clear temporal evolution over the 4 week data set on Arctic haze is obvious with the exception of the extinction coefficient and the lidar ratio, which significantly decreased below 2 km altitude by end April. In altitudes between 2 and 5 km the haze season lasted longer and the aerosol properties were generally more homogeneous than closer to the surface. Above 5 km only few particles were found. The variability of the lidar ratio is discussed. It was found that knowledge of the aerosol’s size and shape does not determine the lidar ratio. Contrary to shape and lidar ratio, there is a clear correlation between size and backscatter: larger particles show a higher backscatter coefficient.
Keywords: Aerosol; Optical properties; Lidar; Lidar ratio; Arctic atmosphere;

Trans-boundary aerosol transport during a winter haze episode in China revealed by ground-based Lidar and CALIPSO satellite by Kai Qin; Lixin Wu; Man Sing Wong; Husi Letu; Mingyu Hu; Hongmei Lang; Shijie Sheng; Jiyao Teng; Xin Xiao; Limei Yuan (20-29).
By employing PM2.5 observation data, ground-based lidar measurements, MODIS and CALIPSO satellite images, meteorological data, and back trajectories analysis, we investigate a trans-boundary transport of aerosols during a large-area haze episode in China during 3–5 January 2015. The ground-based lidar observations indicated similar episodes of external aerosols passing through and mixing into three East China cities. A considerable amount of total AOD below 3 km (46% in average) was contributed by the external aerosol layers during passing over and importing. CALIPSO satellite observations of central and eastern China revealed a high altitude pollutant belt on January 3. Although the severest ground pollution was found in central and south-eastern Hebei, the high altitude pollution transport was greater in south-western Shandong, north-western Jiangsu, and north-western Anhui. These observations along with the analysis of air mass trajectories and wind fields indicates pollutants moving from Hebei, Henan and Hubei probably contributed to the haze pollution in Shandong and Jiangsu. This study reveals haze transports from North China Plain to East China could be a common phenomenon influenced by the winter monsoon in northern China. Hence, effective control of air pollution requires collaboration among different cities and provinces throughout China. The long-term measurements of aerosol vertical properties by ground-based lidar and CALIPSO are extremely valuable in quantifying the contributions of external factors and will be helpful in validating and improving various air quality models.
Keywords: Haze; PM2.5; Aerosol; Lidar; CALIPSO; Trans-boundary transport;

New particle formation under the influence of the long-range transport of air pollutants in East Asia by Indra Chandra; Seyoung Kim; Takafumi Seto; Yoshio Otani; Akinori Takami; Ayako Yoshino; Satoshi Irei; Kihong Park; Tamio Takamura; Naoki Kaneyasu; Shiro Hatakeyama (30-40).
Field observations to investigate the correlation between New Particle Formation (NPF) and the long-range transport of air pollutants in the East Asia region were carried out on a rural Island of Japan in the East-China Sea (Fukue Island, 32.8°N, 128.7°E) over three periods (February 23 to March 7, 2013; November 7 to 20, 2013; and November 2 to 24, 2014). Frequent NPF events were identified (16 events in 50 days), typically in association with sudden increases in particle number concentrations and the successive growth of particles to mobility diameters of several tens of nanometers. The NPF events were classified into two types (A and B) according to the initially detected particle sizes (onset diameters). Type-A consisted of strong NPF events with onset diameters as small as 5 nm. Type-B consisted of NPF events whose onset (<10 nm) was not clearly identifiable. The correlations of SO2 concentrations, solar radiation, PM2.5 concentrations, and chemical composition were analyzed based on the types of NPF events.
Keywords: New particle formation; Aerosol; Long-range transport; East Asia;

Contribution of methane to aerosol carbon mass by F. Bianchi; P. Barmet; L. Stirnweis; I. El Haddad; S.M. Platt; M. Saurer; C. Lötscher; R. Siegwolf; A. Bigi; C.R. Hoyle; P.F. DeCarlo; J.G. Slowik; A.S.H. Prévôt; U. Baltensperger; J. Dommen (41-47).
Small volatile organic compounds (VOC) such as methane (CH4) have long been considered non-relevant to aerosol formation due to the high volatility of their oxidation products. However, even low aerosol yields from CH4, the most abundant VOC in the atmosphere, would contribute significantly to the total particulate carbon budget. In this study, organic aerosol (OA) mass yields from CH4 oxidation were evaluated at the Paul Scherrer Institute (PSI) smog chamber in the presence of inorganic and organic seed aerosols. Using labeled 13C methane, we could detect its oxidation products in the aerosol phase, with yields up to 0.09 + 0.26 − 0.09 %. Overall, we estimate a maximum contribution of CH4 oxidation of 0.13% to the total global organic aerosol budget. We present evidence that oxidation of formaldehyde, a product of methane oxidation, contributes only a minor fraction to the observed aerosol yields. Therefore, other mechanisms appear to be more important for OA production from CH4 oxidation. A thorough elucidation of such mechanisms is still required. However, our results imply that many other small, volatile, and abundant hydrocarbons thus far considered irrelevant for OA production may contribute to the atmospheric OA budget.
Keywords: Methane; VOC; OH oxidation; Secondary organic aerosol; Aerosol yield; Stable isotope;

Effective modelling of atmospheric volcanic ash dispersion is important to ensure aircraft safety, and has been the subject of much study since the Eyjafjallajökull ash crisis in Europe in 2010. In this paper, a novel modelling method is presented, where the atmospheric transport of the 2011 Grímsvötn ash cloud is simulated using a data insertion update scheme. Output from the volcanic ash transport and dispersion model, NAME, is updated using satellite retrievals and the results of a probabilistic ash, cloud and clear sky classification algorithm. A range of configurations of the scheme are compared with each other, in addition to a simple data insertion method presented in a previous study. Results show that simulations in which ash layer heights and depths are updated using the model output generally perform worse in relation to satellite derived ash coverage and ash column loading than simulations that use satellite-retrieved heights and an assumed layer depth of 1.0 km. Simulated ash column loading and concentration tends to be under-predicted using this update scheme, but the timing of the arrival of the ash cloud at Stockholm is well captured, as shown by comparison with lidar-derived mass concentration profiles. Most of the updated simulations in this comparison make small gains in skill on the simple data insertion scheme.
Keywords: Grímsvötn ash cloud; Dispersion modelling; Satellite retrievals; Data insertion;

Comparison among NH3 and GHGs emissive patterns from different housing solutions of dairy farms by Cecilia Baldini; Federica Borgonovo; Davide Gardoni; Marcella Guarino (60-66).
Agriculture and livestock farming are known to be activities emitting relevant quantities of atmospheric pollutants. In particular, in intensive animal farming, buildings can be identified as a relevant source of ammonia and greenhouse gases. This study aimed at: i) determining the emission factors of NH3, N2O, CH4, and CO2 from different dairy farms in Italy, and ii) assessing the effects of the different floor types and manure-handling systems used, in order to minimize the impact of this important productive sector.A measurement campaign was carried out for 27 months in four naturally ventilated dairy cattle buildings with different floor types, layouts and manure management systems, representative of the most common technologies in the north of Italy. Gas emissions were measured with the “static chamber method”: a chamber was placed above the floor farm and an infrared photoacoustic detector (IPD) was used to monitor gas accumulation over time.In the feeding alleys, emissions of NH3 were higher from solid floors than from flushing systems and perforated floors. N2O emissions were significantly different among farms but the absolute values were relatively low. CH4 and CO2 emissions were higher from perforated floors than from other types of housing solution. Regarding the cubicles, the emissions of NH3 were approximately equal from the two housing solution studied. Contrariwise, N2O, CH4 and CO2 emissions were different between the cubicles with rubber mat and those with straw where the highest values were found.
Keywords: Dairy; Emissions; Ammonia; GHGs; Housing solutions; Manure handling;

Experimental and numerical investigations of the geometry influence on gas accumulation using a V-shaped forest model by Bruno Coudour; Khaled Chetehouna; Boris Conan; Sandrine Aubrun; Ahmed Kaiss; Jean-Pierre Garo (67-79).
Accumulation of gas inside a valley exposed to crosswind is experimented in this paper to extrapolate it to a case of a forest fire approaching a thalweg. Experimentations were done inside a wind tunnel using a 1/400 forest model configured as a valley with two different internal angles. The forest was modelled by mesh cylinders so that a parallel is possible with a real forest thanks to similitude laws. Gas emission was ensured by 400 tubes introduced inside the cylinders and supplied with ethane which acted as a tracer. The 400 tubes were divided into four independent parts of 100 tubes, inside and outside the valley, to be able to study independently the influence of the different zones of the forest model on the gas accumulation. We focused on the measurements of velocity by Laser-Doppler Velocimetry (LDV) and concentration with a Flame Ionization Detector (FID) to visualise the flow and quantify the accumulation of ethane. Analysing velocity, turbulence and concentration, a stagnation point was observed in the thalweg for the flattest valley and a recirculation zone for the deepest one where gas accumulation reached up to four times the concentration measured outside the valley due to airflow. The study of the influence of the different emission zones showed that gas accumulation mainly comes from the zones inside the valley. All these data permitted us to validate a numerical modelling which will enable us to study more cases, varying above all gas density but also choosing more valley angles and configurations. Another interest of the numerical model is the possibility of adding a thermal model.
Keywords: V-shaped forest model; Gas accumulation; Wind tunnel; Extreme forest fires; CFD numerical modelling;

Although implementing Diesel particulate filters (DPF) and other novel aftertreatment technologies makes it possible to achieve significant reductions in particle mass emissions, it may induce the release of ultrafine particles and emissions of many other unregulated compounds. This paper focuses on (i) ultrafine particles, black carbon, BTEX, PAH, carbonyl compounds, and NO2 emissions from Euro 4 and Euro 5 Diesel and gasoline passenger cars, (ii) the influence of driving conditions (e.g., cold start, urban, rural and motorway conditions), and (iii) the impact of additive and catalysed DPF devices on vehicle emissions. Chassis dynamometer tests were conducted on four Euro 5 vehicles and two Euro 4 vehicles: gasoline vehicles with and without direct injection system and Diesel vehicles equipped with additive and catalysed particulate filters. The results showed that compared to hot-start cycles, cold-start urban cycles increased all pollutant emissions by a factor of two. The sole exception was NO2, which was reduced by a factor of 1.3–6. Particulate and black carbon emissions from the gasoline engines were significantly higher than those from the Diesel engines equipped with DPF. Moreover, the catalysed DPF emitted about 3–10 times more carbonyl compounds and particles than additive DPF, respectively, during urban driving cycles, while the additive DPF vehicles emitted 2 and 5 times more BTEX and carbonyl compounds during motorway driving cycles. Regarding particle number distribution, the motorway driving cycle induced the emission of particles smaller in diameter (mode at 15 nm) than the urban cold-start cycle (mode at 80–100 nm). The results showed a clear positive correlation between particle, black carbon, and BTEX emissions, and a negative correlation between particles and NO2.
Keywords: Unregulated pollutant emission; Chassis dynamometer; Driving conditions; Diesel particulate filter; Regeneration;

Flux estimation of fugitive particulate matter emissions from loose Calcisols at construction sites by Hala A. Hassan; Prashant Kumar; Konstantinos E. Kakosimos (96-105).
A major source of airborne pollution in arid and semi-arid environments (i.e. North Africa, Middle East, Central Asia, and Australia) is the fugitive particulate matter (fPM), which is a frequent product of wind erosion. However, accurate determination of fPM is an ongoing scientific challenge. The objective of this study is to examine fPM emissions from the loose Calcisols (i.e. soils with a substantial accumulation of secondary carbonates), owing to construction activities that can be frequently seen nowadays in arid urbanizing regions such as the Middle East. A two months field campaign was conducted at a construction site, at rest, within the city of Doha (Qatar) to measure number concentrations of PM over a size range of 0.25–32 μm using light scattering based monitoring stations. The fPM emission fluxes were calculated using the Fugitive Dust Model (FDM) in an iterative manner and were fitted to a power function, which expresses the wind velocity dependence. The power factors were estimated as 1.87, 1.65, 2.70 and 2.06 for the four different size classes of particles ≤2.5, 2.5–6, 6–10 and ≤10 μm, respectively. Fitted power function was considered acceptable given that adjusted R 2 values varied from 0.13 for the smaller particles and up to 0.69 for the larger ones. These power factors are in the same range of those reported in the literature for similar sources. The outcome of this study is expected to contribute to the improvement of PM emission inventories by focusing on an overlooked but significant pollution source, especially in dry and arid regions, and often located very close to residential areas and sensitive population groups. Further campaigns are recommended to reduce the uncertainty and include more fPM sources (e.g. earthworks) and other types of soil.
Keywords: Air pollution; Construction emissions; Fugitive particulate matter; Carbonates; Calcisols; Middle-east region;

Seasonal monitoring and estimation of regional aerosol distribution over Po valley, northern Italy, using a high-resolution MAIAC product by Barbara Arvani; R. Bradley Pierce; Alexei I. Lyapustin; Yujie Wang; Grazia Ghermandi; Sergio Teggi (106-121).
In this work, the new 1 km-resolved Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is employed to characterize seasonal PM10 – AOD correlations over northern Italy. The accuracy of the new dataset is assessed compared to the widely used Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5.1 Aerosol Optical Depth (AOD) data, retrieved at 0.55 μm with spatial resolution of 10 km (MYD04_L2). We focused on evaluating the ability of these two products to characterize both temporal and spatial distributions of aerosols within urban and suburban areas. Ground PM10 measurements were obtained from 73 of the Italian Regional Agency for Environmental Protection (ARPA) monitoring stations, spread across northern Italy, during a three-year period from 2010 to 2012. The Po Valley area (northern Italy) was chosen as the study domain because of its severe urban air pollution, resulting from it having the highest population and industrial manufacturing density in the country, being located in a valley where two surrounding mountain chains favor the stagnation of pollutants. We found that the global correlations between the bin-averaged PM10 and AOD are R2 = 0.83 and R2 = 0.44 for MYD04_L2 and for MAIAC, respectively, suggesting a greater sensitivity of the high-resolution product to small-scale deviations. However, the introduction of Relative Humidity (RH) and Planetary Boundary Layer (PBL) depth corrections allowed for a significant improvement to the bin-averaged PM – AOD correlation, which led to a similar performance: R2 = 0.96 for MODIS and R2 = 0.95 for MAIAC. Furthermore, the introduction of the PBL information in the corrected AOD values was found to be crucial in order to capture the clear seasonal cycle shown by measured PM10 values. The study allowed us to define four seasonal linear correlations that estimate PM10 concentrations satisfactorily from the remotely sensed MAIAC AOD retrieval. Overall, the results show that the high resolution provided by MAIAC retrieval data is much more relevant than the 10 km MODIS data to characterize PM10 in this region of Italy which has a pretty limited geographical domain but a broad variety of land usages and consequent particulate concentrations.
Keywords: Aerosol optical depth (AOD); High resolution aerosol retrieval; Seasonality AOD-PM10 correlation; MAIAC; MODIS; PM10; Planetary boundary layer (PBL);

A new method is proposed for estimating the rate of fugitive emissions of particulate matter from multiple time-dependent sources via measurements of deposition and concentration. We cast this source inversion problem within the Bayesian framework, and use a forward model based on a Gaussian plume solution. We present three alternate models for constructing the prior distribution on the emission rates as functions of time. Next, we present an industrial case study in which our framework is applied to estimate the rate of fugitive emissions of lead particulates from a smelter in Trail, British Columbia, Canada. The Bayesian framework not only provides an approximate solution to the inverse problem, but also quantifies the uncertainty in the solution. Using this information we perform an uncertainty propagation study in order to assess the impact of the estimated sources on the area surrounding the industrial site.
Keywords: Pollutant dispersion; Gaussian plume; Particle deposition; Inverse problem; Bayesian estimation;

In this work, we analysed reactive gases (O3, CO, NOx) and aerosol properties (eqBC, σs and particle number concentration) collected at the WMO/GAW Mt. Cimone station (2165 m a.s.l., Italy) during the summer of 2012 in the framework of PEGASOS project. The major aim of this experiment is providing a characterization of the variability of summer atmospheric composition over the central Mediterranean basin, which is considered as a global “hot-spot” for atmospheric pollution and climate change.The atmospheric tracers have been analysed as a function of (i) meteorological parameters, (ii) synoptic-scale circulation and (iii) anthropogenic emission source proximity as estimated by O3/NOx ratio variability. In particular, we identified three O3/NOx regimes which tagged the distance of anthropogenic sources: near outflow (23% of hourly data), far-outflow (38% of data) and background (39% of data). The highest levels of anthropogenic pollutants (e.g. O3, CO, eqBC, accumulation particles) were concomitant with fresh emissions from northern Italy under near-outflow conditions: once injected to the free troposphere, these air-masses, rich in pollutants and climate-forcers (i.e. O3, eqBC) and soil dust, can be spread over a large region, thus significantly affecting regional climate. Moreover, based on the anthropogenic source proximity, atmospheric tracer variability and synoptic-scale atmospheric circulation, we categorized and characterised four types of atmospheric regimes associated with (1) air-mass transport from the free troposphere, (2) transport of fresh emitted pollutants from the PBL, (3) transport at regional/continental scale of aged anthropogenic (4) transport of air-mass rich in mineral dust from northern Africa (i.e. coming from more than 1000 km).Lastly, by analysing the probability density functions (PDFs) of trace gases and aerosol properties, “fingerprints” of the mentioned atmospheric regimes were pointed out. Such information is useful for the implementation of early-warning services, for the timely detection of event occurrence as well as for the definition of observation-based diagnostic for model verifications.
Keywords: Mediterranean basin; Po basin; Short-lived climate forcers/pollutants; Air-mass age; Air-mass transport;

Exchange of polycyclic aromatic hydrocarbons across the air-water interface in the Bohai and Yellow Seas by Yingjun Chen; Tian Lin; Jianhui Tang; Zhiyong Xie; Chongguo Tian; Jun Li; Gan Zhang (153-160).
In this study, air and surface seawater samples collected from the Bohai (BS) and Yellow Seas (YS) in May 2012 were determined exchange of PAHs, especially of low-molecular-weight (LMW) PAHs (three- and four-ring PAHs) at the air-water interface. Net volatilization fluxes of LMW PAHs were 266–1454 ng/m2/d and decreased with distance from the coast, indicating that these PAHs transported from coastal runoff were potential contributors to the atmosphere in the BS and YS. Moreover, LMW PAHs were enriched in the dissolved phase compared with those in the particulate phase in the water column, possibly suggesting that the volatilized LMW PAHs were directly derived from wastewater discharge or petroleum pollution rather than released from contaminated sediments. The air–sea exchange fluxes of the three-ring PAHs were 2- to 20-fold higher than their atmospheric deposition fluxes in the BS and YS. The input to and output from the water reached equilibrium for four-ring PAHs. Differently, five- and six-ring PAHs were introduced into the marine environment primarily through dry and wet deposition, indicating that the water column was still a sink of these PAHs from the surrounding atmosphere.
Keywords: PAHs; Air-sea exchange; Net volatilization; Particle–water partitioning; The Bohai and Yellow Seas;

A novel mobile monitoring approach to characterize spatial and temporal variation in traffic-related air pollutants in an urban community by Chang Ho Yu; Zhihua Fan; Paul J. Lioy; Ana Baptista; Molly Greenberg; Robert J. Laumbach (161-173).
Air concentrations of traffic-related air pollutants (TRAPs) vary in space and time within urban communities, presenting challenges for estimating human exposure and potential health effects. Conventional stationary monitoring stations/networks cannot effectively capture spatial characteristics. Alternatively, mobile monitoring approaches became popular to measure TRAPs along roadways or roadsides. However, these linear mobile monitoring approaches cannot thoroughly distinguish spatial variability from temporal variations in monitored TRAP concentrations. In this study, we used a novel mobile monitoring approach to simultaneously characterize spatial/temporal variations in roadside concentrations of TRAPs in urban settings. We evaluated the effectiveness of this mobile monitoring approach by performing concurrent measurements along two parallel paths perpendicular to a major roadway and/or along heavily trafficked roads at very narrow scale (one block away each other) within short time period (<30 min) in an urban community. Based on traffic and particulate matter (PM) source information, we selected 4 neighborhoods to study. The sampling activities utilized real-time monitors, including battery-operated PM2.5 monitor (SidePak), condensation particle counter (CPC 3007), black carbon (BC) monitor (Micro-Aethalometer), carbon monoxide (CO) monitor (Langan T15), and portable temperature/humidity data logger (HOBO U12), and a GPS-based tracker (Trackstick). Sampling was conducted for ∼3 h in the morning (7:30–10:30) in 7 separate days in March/April and 6 days in May/June 2012. Two simultaneous samplings were made at 5 spatially-distributed locations on parallel roads, usually distant one block each other, in each neighborhood. The 5-min averaged BC concentrations (AVG ± SD, [range]) were 2.53 ± 2.47 [0.09–16.3] μg/m3, particle number concentrations (PNC) were 33,330 ± 23,451 [2512–159,130] particles/cm3, PM2.5 mass concentrations were 8.87 ± 7.65 [0.27–46.5] μg/m3, and CO concentrations were 1.22 ± 0.60 [0.22–6.29] ppm in the community. The traffic-related air pollutants, BC and PNC, but not PM2.5 or CO, varied spatially depending on proximity to local stationary/mobile sources. Seasonal differences were observed for all four TRAPs, significantly higher in colder months than in warmer months. The coefficients of variation (CVs) in concurrent measurements from two parallel routes were calculated around 0.21 ± 0.17, and variations were attributed by meteorological variation (25%), temporal variability (19%), concentration level (6%), and spatial variability (2%), respectively. Overall study findings suggest this mobile monitoring approach could effectively capture and distinguish spatial/temporal characteristics in TRAP concentrations for communities impacted by heavy motor vehicle traffic and mixed urban air pollution sources.
Keywords: Mobile monitoring; Traffic-related air pollution; Spatial and temporal variability; Parallel measurement; Traffic proximity; Road exposure;

The upper tropospheric methane (UCH4) data from Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC), the column average mixing ratio of methane (XCH4) from SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and near-surface methane at two locations- Cape Rama, Goa, a Commonwealth Scientific Industrial Research Organization (CSIRO) network station and Ahmedabad (23.03°N; 72.45°E) were analysed to understand vertical inhomogenities in methane mixing ratio and the seasonal changes in the latitude sector 13°–24°N over India. XCH4 and UCH4 were found to follow more or less similar pattern over all the three latitude sectors, with the peak occurring in July–August, and minimum in late winter. The seasonal amplitude in XCH4 is less at low latitude sector (∼64 ppbv) compared to that of high latitudes (∼101 ppbv at 18°–22°N and 88 ppbv at 22°–24°N). On the other hand, the near surface methane shows opposite pattern peaking in winter attaining low in monsoon. During monsoon when methane sources are active at the surface, XCH4 > UCH4 and during other seasons UCH4 > XCH4 indicating presence of high altitude layers. This analysis revealed non-homogeneous distribution of methane in the troposphere indicative of stratified layers. The role of convective activity, boundary layer meteorology and long-range transport in controlling the seasonal changes in the vertical distribution of methane are examined in this study.
Keywords: Methane; SCIAMACHY; CARIBIC; Vertical distribution; Seasonal change;

On the influence of the diurnal variations of aerosol content to estimate direct aerosol radiative forcing using MODIS data by Hui Xu; Jianping Guo; Xavier Ceamanos; Jean-Louis Roujean; Min Min; Dominique Carrer (186-196).
Long-term measurements of aerosol optical depth (AOD) from the Aerosol Robotic Network (AERONET) located in Beijing reveal a strong diurnal cycle of aerosol load staged by seasonal patterns. Such pronounced variability is matter of importance in respect to the estimation of daily averaged direct aerosol radiative forcing (DARF). Polar-orbiting satellites could only offer a daily revisit, which turns in fact to be even much less in case of frequent cloudiness. Indeed, this places a severe limit to properly capture the diurnal variations of AOD and thus estimate daily DARF. Bearing this in mind, the objective of the present study is however to evaluate the impact of AOD diurnal variations for conducting quantitative assessment of DARF using Moderate Resolution Imaging Spectroradiometer (MODIS) AOD data over Beijing. We provide assessments of DARF with two different assumptions about diurnal AOD variability: taking the observed hourly-averaged AOD cycle into account and assuming constant MODIS (including Terra and Aqua) AOD value throughout the daytime. Due to the AOD diurnal variability, the absolute differences in annual daily mean DARFs, if the constant MODIS/Terra (MODIS/Aqua) AOD value is used instead of accounting for the observed hourly-averaged daily variability, is 1.2 (1.3) Wm−2 at the top of the atmosphere, 27.5 (30.6) Wm−2 at the surface, and 26.4 (29.3) Wm−2 in the atmosphere, respectively. During the summertime, the impact of the diurnal AOD variability on seasonal daily mean DARF estimates using MODIS Terra (Aqua) data can reach up to 2.2 (3.9) Wm−2 at the top of the atmosphere, 43.7 (72.7) Wm−2 at the surface, and 41.4 (68.8) Wm−2 in the atmosphere, respectively. Overall, the diurnal variation in AOD tends to cause large bias in the estimated DARF on both seasonal and annual scales. In summertime, the higher the surface albedo, the stronger impact on DARF at the top of the atmosphere caused by dust and biomass burning (continental) aerosol. This indicates that the impact on DARFs estimates is sensitive to assumptions of aerosol type and surface albedo.
Keywords: Aerosol optical depth; Aerosol diurnal cycle; Direct aerosol radiative forcing; MODIS; AERONET;

Redefining the importance of nitrate during haze pollution to help optimize an emission control strategy by Yuepeng Pan; Yuesi Wang; Junke Zhang; Zirui Liu; Lili Wang; Shili Tian; Guiqian Tang; Wenkang Gao; Dongsheng Ji; Tao Song; Yonghong Wang (197-202).
Nitrate salts represent a major component of fine mode aerosols, which play an important role in air pollution worldwide. Based on on-line and off-line aerosol measurements in urban Beijing for both clean and haze conditions, we demonstrate that the absolute and relative concentrations of nitrate increased with visibility degradation (relative humidity), whereas the variations of organics tracked the patterns of mixing-layer height and temperature. We propose that the increase in the relative contribution of nitrate to PM1 observed during the early stages of haze pollution was due to new particle formation, whereas the nitrate formed in PM1-2.5 during the latter stages was due to heterogeneous formation and hygroscopic growth. The increasing trend of nitrate (and also sulfate and ammonium) but decreasing trends of organics during haze development, together with the increase of the NO2/SO2 molar ratio with increasing proximity to downtown Beijing and with visibility degradation, provide further evidence that controlling NO x emissions should be a priority for improving air quality in mega cities. Additional large-scale investigation is required to adequately characterize the regional features of NO x -induced haze pollution in China. Such studies may provide insight into the formation of critical nuclei or the subsequent growth of freshly nucleated particles and advance our understanding of the role of nitrate in new particle formation.Display Omitted
Keywords: Haze pollution; Nitrate; Particulate matter; Mitigation strategy; China;

Carbonaceous matter deposition in the high glacial regions of the Tibetan Plateau by Chaoliu Li; Pengfei Chen; Shichang Kang; Fangping Yan; Xiaofei Li; Bin Qu; Mika Sillanpää (203-208).
Carbonaceous matter at glacial region plays important role in river ecosystems fed by glacier and albedo reduction of glacier surface. However, currently, limited knowledge are available on the carbonaceous matter within the glacial region of the Tibetan Plateau (TP). In this study, the data from six snowpits in the glacial region across the TP were reported. The results showed that dissolved organic carbon (DOC) concentrations of snowpit samples of the TP were comparable to those of European Alps and the Arctic. The ratio of DOC to carbonaceous matter (40.25 ± 8.98%) was lower than that of Alpine glaciers, thus indicating greater particulate carbon content in the TP glacial region. In addition, the DOC was significantly correlated with insoluble particulate carbon (IPC), indicating that IPC and DOC likely came from the same sources. Spatially, the DOC concentration decreased from the north (0.42 ± 0.29 mg-C L−1) to the south TP (0.15 ± 0.06 mg-C L−1), which was consistent with variations in the distribution of dust storm on the TP. Principal component analysis of major ions and DOC showed that mineral dust contributed the major part of DOC, followed by biogenic sources such as agriculture and livestock. Finally, based on DOC concentrations and precipitation amounts at different periods, the mean annul flux of DOC in the glacial region of the TP was calculated to be 0.11 ± 0.05 g-C m−2 yr−1.
Keywords: Carbonaceous matter; Dissolved organic carbon; Flux; The Tibetan Plateau; Glacier;

One of the potential environmental issues associated with oil sands development is increased ozone formation resulting from NOX and volatile organic compound emissions from bitumen extraction, processing and upgrading. To manage this issue in the Athabasca Oil Sands Region (AOSR) in northeast Alberta, a regional multi-stakeholder group, the Cumulative Environmental Management Association (CEMA), developed an Ozone Management Framework that includes a modelling based assessment component. In this paper, we describe how the Community Multi-scale Air Quality (CMAQ) model was applied to assess potential ground-level ozone formation and impacts on ambient air quality and vegetation health for three different ozone precursor cases in the AOSR. Statistical analysis methods were applied, and the CMAQ performance results met the U.S. EPA model performance goal at all sites. The modelled 4th highest daily maximum 8-h average ozone concentrations in the base and two future year scenarios did not exceed the Canada-wide standard of 65 ppb or the newer Canadian Ambient Air Quality Standards of 63 ppb in 2015 and 62 ppb in 2020. Modelled maximum 1-h ozone concentrations in the study were well below the Alberta Ambient Air Quality Objective of 82 ppb in all three cases. Several ozone vegetation exposure metrics were also evaluated to investigate the potential impact of ground-level ozone on vegetation. The chronic 3-months SUM60 exposure metric is within the CEMA baseline range (0–2000 ppb-hr) everywhere in the AOSR. The AOT40 ozone exposure metric predicted by CMAQ did not exceed the United Nations Economic Commission for Europe (UN/ECE) threshold of concern of 3000 ppb-hr in any of the cases but is just below the threshold in high-end future emissions scenario. In all three emission scenarios, the CMAQ predicted W126 ozone exposure metric is within the CEMA baseline threshold of 4000 ppb-hr. This study outlines the use of photochemical modelling of the impact of an industry (oil sands) on ground-level ozone levels as an air quality management tool in the AOSR. It allows an evaluation of the relationships between the pollutants emitted to the atmosphere and potential ground level ozone concentrations throughout the AOSR thereby extending the spatial coverage of the results beyond the monitoring network and also allowing an assessment of the potential impacts of possible future emission cases.
Keywords: Ground-level ozone; Community Multi-scale Air Quality model; Athabasca oil sands region; Air quality; Ozone impact on vegetation; Emission scenarios;

Trace metal species and surface active agent (surfactant) emitted into the atmosphere from natural and anthropogenic source can cause various health related and environmental problems. Limited data exists for determinations of atmospheric particulate matter particularly trace metals and surfactant concentration in Malaysia during biomass burning haze episode. We used simple and validated effective methodology for the determination of trace metals and surfactant in atmospheric particulate matter (TSP & PM2.5) collected during the biomass burning haze episode in Kampar, Malaysia from end of August to October 2015. Colorimetric method of analysis was undertaken to determine the concentration of anionic surfactant as methylene blue active substance (MBAS) and cationic surfactant as disulphine blue active substance (DBAS) using a UV–Visible spectrophotometer. Particulate samples were also analyzed for trace metals with inductive coupled plasma mass spectrometer (ICP-MS) followed by extraction from glass microfiber filters with close vessel microwave acid digestion. The result showed that the concentrations of surfactant in both samples (TSP & PM2.5) were dominated by MBAS (0.147–4.626 mmol/m3) rather than DBAS (0.111–0.671 mmol/m3) and higher than the other researcher found. Iron (147.31–1381.19 μg/m3) was recorded leading trace metal in PM followed by Al, Zn, Pb, Cd, Cr and others. During the haze period the highest mass concentration of TSP 313.34 μg/m3 and 191.07 μg/m3 for PM2.5 were recorded. Furthermore, the backward air trajectories from Kampar in north of peninsular Malaysia confirmed that nearly all the winds paths originate from Sumatera and Kalimantan, Indonesia.
Keywords: Biomass burning; Trace metals; Surfactant; ICP-MS; UV/Vis spectrometer;

Mercury is an important pollutant that can be transported globally due to its long lifetime in the atmosphere. Atmosphere-surface exchange is a major process affecting the cycling of mercury in the global environment and its impacts on food webs. We investigate the sensitivities of the air-surface exchange, atmospheric transport, and budget of mercury to projected 2000–2050 changes in climate and land use/land cover with a global chemical transport model (GEOS-Chem). We find that annual mean Hg(0) dry deposition flux over land could increase by up to 20% in northern mid-latitudes by 2050 due to increased vegetation and foliage density. Climate change can significantly affect both the wet deposition and atmospheric chemistry of mercury. In response to the projected climate change, the annual mean wet deposition flux increases over most continental regions and decreases over most of the mid-latitude and tropical oceans. The annual mean mercury wet deposition flux over northern and southern high latitudes increases by 7% and 8% respectively, largely driven by increases in precipitation there. Surface Hg(0) is predicted to increase generally, because high temperatures decrease Hg(0) oxidation by bromine and high moisture increases aqueous Hg(II) photo reduction. The combined effects of projected changes in climate, land use and land cover increase mercury deposition to the continental biosphere and decrease mercury deposition to the marine biosphere.
Keywords: Climate change; Land use/land cover change; Atmospheric mercury; Mercury deposition;

One of the shortcomings of closed chamber methods for soil respiration (SR) measurements is the decreased CO2 diffusion rate from soil to chamber headspace that may occur due to increased chamber CO2 concentrations. This feedback on diffusion rate may lead to underestimation of pre-deployment fluxes by linear regression techniques. Thus, usually the cumulative flux curve becomes downward concave due to the decreased gas diffusion rate. Non-linear models based on biophysical theory usually fit to such curvatures and may reduce the underestimation of fluxes. In this study, we examined the effect of increasing chamber enclosure time on SR flux rates calculated using a linear, an exponential and a revised Hutchinson and Mosier model (HMR). Soil respiration rates were measured with a closed chamber in combination with an infrared gas analyzer. During SR flux measurements the chamber was placed on fixed collars, and CO2 concentration in the chamber headspace were recorded at 1-s intervals for 45 min. Fluxes were measured in different soil types (sandy, sandy loam and organic soils), and for various manipulations (tillage, rain and drought) and soil conditions (temperature and moisture) to obtain a range of fluxes with different shapes of flux curves. The linear method provided more stable flux results during short enclosure times (few min) but underestimated initial fluxes by 15–300% after 45 min deployment time. Non-linear models reduced the underestimation as average underestimation was only about 10% after 45 min for regular flux curves. For irregular flux curves with a rapid increase in CO2 concentration immediately after chamber deployment it was shown that short enclosure times were prone to overestimation of pre-deployment fluxes, but this was mitigated by longer enclosure times (>10–15 min).
Keywords: Chamber enclosure time; Flux estimation; Linear regression; Non-linear regression;

Technical note: Examining ozone deposition over seawater by Golam Sarwar; Daiwen Kang; Kristen Foley; Donna Schwede; Brett Gantt; Rohit Mathur (255-262).
Surface layer resistance plays an important role in determining ozone deposition velocity over sea-water and can be influenced by chemical interactions at the air-water interface. Here, we examine the effect of chemical interactions of iodide, dimethylsulfide, dissolved organic carbon, and bromide in seawater on ozone deposition. We perform a series of simulations using the hemispheric Community Multiscale Air Quality model for summer months in the Northern Hemisphere. Our results suggest that each chemical interaction enhances the ozone deposition velocity and decreases the atmospheric ozone mixing ratio over seawater. Iodide enhances the median deposition velocity over seawater by 0.023 cm s−1, dissolved organic carbon by 0.021 cm s−1, dimethylsulfide by 0.002 cm s−1, and bromide by ∼0.0006 cm s−1. Consequently, iodide decreases the median atmospheric ozone mixing ratio over seawater by 0.7 ppb, dissolved organic carbon by 0.8 ppb, dimethylsulfide by 0.1 ppb, and bromide by 0.02 ppb. In a separate model simulation, we account for the effect of dissolved salts in seawater on the Henry’s law constant for ozone and find that it reduces the median deposition velocity by 0.007 cm s−1 and increases surface ozone mixing ratio by 0.2 ppb. The combined effect of these processes increases the median ozone deposition velocity over seawater by 0.040 cm s−1, lowers the atmospheric ozone mixing ratio by 5%, and slightly improves model performance relative to observations.
Keywords: Iodide; Dimethylsulfide; Dissolved organic carbon; Ozone; Deposition;

Multi-year levels and trends of non-methane hydrocarbon concentrations observed in ambient air in France by Antoine Waked; Stéphane Sauvage; Agnès Borbon; Julie Gauduin; Cyril Pallares; Marie-Pierre Vagnot; Thierry Léonardis; Nadine Locoge (263-275).
Measurements of 31 non-methane hydrocarbons (NMHCs) were carried out at three urban (Paris, 2003–2014, Strasbourg, 2002–2014 and Lyon, 2007–2014) sites in France over the period of a decade. A trend analysis was applied by means of the Mann-Kendall non-parametric test to annual and seasonal mean concentrations in order to point out changes in specific emission sources and to assess the impact of emission controls and reduction strategies. The trends were compared to those from three rural sites (Peyrusse-Vieille, 2002–2013, Tardière, 2003–2013 and Donon, 1997–2007). The results obtained showed a significant yearly decrease in pollutant concentrations over the study period and for the majority of species in the range of −1 to −7% in accordance with the decrease of NMHC emissions in France (−5 to −9%). Concentrations of long-lived species such as ethane and propane which are recognized as tracers of distant sources and natural gas remained constant. Compounds associated with combustion processes such as acetylene, propene, ethylene and benzene showed a significant decline in the range of −2% to −5% yr−1. These trends are consistent with those recently described at urban and background sites in the northern mid-latitudes and with emission inventories. C7-C9 aromatics such as toluene and xylenes as well as C4-C5 alkanes such as isopentane and isobutane also showed a significant decrease in the range of −3% to −7% yr−1. The decreasing trends in terms of % yr−1 observed at these French urban sites were typically higher for acetylene, ethylene and benzene than those reported for French rural sites of the national observatory of Measurement and Evaluation in Rural areas of trans-boundary Air pollution (MERA). The study also highlighted the difficult choice of a long term sampling site representative of the general trends of pollutant concentrations.
Keywords: VOC; Ambient concentration; Temporal trend; Emission control; Vehicle exhaust; Solvent;

Evaluation of biomass burning across North West Europe and its impact on air quality by R.L. Cordell; M. Mazet; C. Dechoux; S.M.L. Hama; J. Staelens; J. Hofman; C. Stroobants; E. Roekens; G.P.A. Kos; E.P. Weijers; K.F.A. Frumau; P. Panteliadis; T. Delaunay; K.P. Wyche; P.S. Monks (276-286).
Atmospheric particulate pollution is a significant problem across the EU and there is concern that there may be an increasing contribution from biomass burning, driven by rising fuel prices and an increased interest in the use of renewable energy sources. This study was carried out to assess current levels of biomass burning and the contribution to total PM10 across five sites in North-West Europe; an area which is frequently affected by poor air quality. Biomass burning was quantified by the determination of levoglucosan concentrations from PM10 aerosol filters collected over a 14 month period in 2013/2014 and continued for a further 12 months at the UK site in Leicester. Levoglucosan levels indicated a distinct period of increased biomass combustion between November and March. Within this period monthly average concentrations ranged between 23 ± 9.7 and 283 ± 163 ng/m3, with Lille showing consistently higher levels than the sites in Belgium, the Netherlands and the UK. The estimated contribution to PM10 was, as expected, highest in the winter season where the season average percentage contribution was lowest in Wijk aan Zee at 2.7 ± 1.4% and again highest in Lille at 11.6 ± 3.8%, with a PM10 mass concentration from biomass that ranged from 0.56 μg/m3 in Leicester to 2.08 μg/m3 in Lille. Overall there was poor correlation between the levoglucosan concentrations measured at the different sites indicating that normally biomass burning would only affect atmospheric particulate pollution in the local area; however, there was evidence that extreme burning events such as the Easter fires traditionally held in parts of North-West Europe can have far wider ranging effects on air quality. Network validation measurements were also taken using a mobile monitoring station which visited the fixed sites to carry out concurrent collections of aerosol filters; the result of which demonstrated the reliability of both PM10 and levoglucosan measurements.Display Omitted
Keywords: Levoglucosan; Monosaccharide anhydrides; Biomass burning; North-West Europe; PM10;

Parameterization of G-93 isoprene emission formula for tropical trees Casuarina equisetifolia and Ficus septica by Ishmael Mutanda; Masashi Inafuku; Hironori Iwasaki; Seikoh Saitoh; Masakazu Fukuta; Keiichi Watanabe; Hirosuke Oku (287-296).
Tropical trees account for most emissions of isoprene, a reactive biogenic volatile organic compound into the atmosphere. The Guenther 1993 (G-93) model is the most widely used algorithm for predicting isoprene emissions by leaves of terrestrial plants. Several studies have reported on the poor performance of the G-93 model in predicting emissions from tropical tree species. To improve the performance of the G-93 model in tropical regions, we carried out diurnal leaf-scale observations of tropical trees Casuarina equisetifolia and Ficus septica outdoors. We developed an iterative method that uses mutual and repetitive step-by-step optimization of the G-93 parameters for temperature (C T ) and light (C L ) variables using best fit practices, named “Ping-Pong” optimization. Using temperate tree species (Poplar) for comparison, we show that emissions from C. equisetifolia and F. septica had a diversion from predictions of the G-93 formula, especially at high temperatures and high light intensities during mid-day, whilst emissions from temperate tree species were fairly captured by G-93. Results demonstrate that our optimized formulas greatly improved capturing of high light and temperature responses of emission profiles from tropical trees whilst it also performed well for poplar species. Parameterization of the G-93 formula greatly improved its performance on predicting diurnal isoprene emission from tropical trees C. equisetifolia and F. septica; explaining 81–96% of variation up from 73 to 77% explained by default G-93. We propose that there is a need to optimize the G-93 model to more accurately predict regional emissions from tropical ecosystems.
Keywords: G-93 model; Isoprene emission; Tropical tree; Model parameterization; Temperature response; Light response;

Development and application of a high resolution hybrid modelling system for the evaluation of urban air quality by N. Pepe; G. Pirovano; G. Lonati; A. Balzarini; A. Toppetti; G.M. Riva; M. Bedogni (297-311).
A hybrid modelling system (HMS) was developed to provide hourly concentrations at the urban local scale. The system is based on the combination of a meteorological model (WRF), a chemical and transport eulerian model (CAMx), which computes concentration levels over the regional domains, and a lagrangian dispersion model (AUSTAL2000), accounting for dispersion phenomena within the urban area due to local emission sources; a source apportionment algorithm is also included in the HMS in order to avoid the double counting of local emissions.The HMS was applied over a set of nested domains, the innermost covering a 1.6 × 1.6 km2 area in Milan city center with 20 m grid resolution, for NOX simulation in 2010. For this paper the innermost domain was defined as “local”, excluding usual definition of urban areas. WRF model captured the overall evolution of the main meteorological features, except for some very stagnant situations, thus influencing the subsequent performance of regional scale model CAMx. Indeed, CAMx was able to reproduce the spatial and temporal evolution of NOX concentration over the regional domain, except a few episodes, when observed concentrations were higher than 100 ppb. The local scale model AUSTAL2000 provided high-resolution concentration fields that sensibly mirrored the road and traffic pattern in the urban domain. Therefore, the first important outcome of the work is that the application of the hybrid modelling system allowed a thorough and consistent description of urban air quality. This result represents a relevant starting point for future evaluation of pollution exposure within an urban context.However, the overall performance of the HMS did not provide remarkable improvements with respect to stand-alone CAMx at the two only monitoring sites in Milan city center. HMS results were characterized by a smaller average bias, that improved about 6–8 ppb corresponding to 12–13% of the observed concentration, but by a lower correlation, that worsened around 1–3% (e.g. from 0.84 to 0.81 at Senato site), due to the concentration peaks produced by AUSTAL2000 during nighttime stable conditions. Additionally, the HMS results showed that it was unable to correctly take into account some local scale features (e.g. urban canyon effects), pointing out that the emission spatialization and time modulation criteria, especially those from road traffic, need further improvement.Nevertheless, a second important outcome of the work is that some of the most relevant discrepancies between modelled and observed concentrations were not related to the horizontal resolution of the dispersion models but to larger scale meteorological features not captured by the meteorological model, especially during winter period. Finally, the estimated contribution of the local emission sources accounted on the annual average for about 25–30% of the computed concentration levels in the innermost urban domain. This confirmed that the whole Milan urban area as well as the outside background areas, accounting all sources outside the innermost domain, play a key role on air quality. The result suggests that strictly local emission policies could have a limited and indecisive effect on urban air quality, although this finding could be partially biased by model underestimation of the observed concentration.
Keywords: Urban air quality; NOx; Hybrid modelling; CAMx; AUSTAL2000; Milan;

Bulk biofuel, biomass pellets and pelletized biomass-coal blends were combusted in a typical rural conventional household stove and a high-efficiency stove. Reductions in PM2.5, organic carbon (OC) and elemental carbon (EC) emissions were evaluated by comparing emission factors (EFs) among 19 combinations of biofuel/residential stove types measured using a dilution sampling system. In the low-efficiency stove, the average EFs of PM2.5, OC, and EC of biomass pellets were 2.64 ± 1.56, 0.42 ± 0.36, and 0.30 ± 0.11 g/kg, respectively, significantly lower than those burned in bulk form. EFPM2.5 and EFOC of pelletized biomass combustion in the high-efficiency stove were lower than those of the same biofuel burned in the low-efficiency stove. Furthermore, pelletized corn residue and coal blends burned in the high-efficiency stove could significantly decrease emissions. Compared with the bulk material burned in the low-efficiency stove, the reduction rates of PM2.5, OC and EC from pelletized blends in the high-efficiency stove can reach 84%, 96% and 93%, respectively. If the annually produced corn residues in 2010 had been blended with 10% anthracite coal powder and burnt as pellets, it would have reduced about 82% of PM2.5, 90–96% of OC and 81–92% of EC emission in comparison with burning raw materials in conventional household stoves. Given the low cost, high health benefit and reduction effect on atmospheric pollutants, pelletized blends could be a promising alternative to fossil fuel resources or traditional bulk biofuel.
Keywords: PM2.5; OC; EC; Biomass pellets; Pelletized biomass-coal blends;

Inter-comparison of model-simulated and satellite-retrieved componential aerosol optical depths in China by Shenshen Li; Chao Yu; Liangfu Chen; Jinhua Tao; Husi Letu; Wei Ge; Yidan Si; Yang Liu (320-332).
China’s large aerosol emissions have major impacts on global climate change as well as regional air pollution and its associated disease burdens. A detailed understanding of the spatiotemporal patterns of aerosol components is necessary for the calculation of aerosol radiative forcing and the development of effective emission control policy. Model-simulated and satellite-retrieved aerosol components can support climate change research, PM2.5 source appointment and epidemiological studies. This study evaluated the total and componential aerosol optical depth (AOD) from the GEOS-Chem model (GC) and the Global Ozone Chemistry Aerosol Radiation and Transport model (GOCART), and the Multiangle Imaging Spectroradiometer (MISR) from 2006 to 2009 in China. Linear regression analysis between the GC and AErosol RObotic NETwork (AERONET) in China yielded similar correlation coefficients (0.6 daily, 0.71 monthly) but lower slopes (0.41 daily, 0.58 monthly) compared with those in the U.S. This difference was attributed to GC’s underestimation of water-soluble AOD (WAOD) west of the Heihe-Tengchong Line, the dust AOD (DAOD) in the fall and winter, and the soot AOD (SAOD) throughout the year and throughout the country. GOCART exhibits the strongest dust estimation capability among all datasets. However, the GOCART soot distribution in the Northeast and Southeast has significant errors, and its WAOD in the polluted North China Plain (NCP) and the South is underestimated. MISR significantly overestimates the water-soluble aerosol levels in the West, and does not capture the high dust loadings in all seasons and regions, and the SAOD in the NCP. These discrepancies can mainly be attributed to the uncertainties in the emission inventories of both models, the poor performance of GC under China’s high aerosol loading conditions, the omission of certain aerosol tracers in GOCART, and the tendency of MISR to misidentify dust and non-dust mixtures.
Keywords: GEOS-Chem; GOCART; MISR; AERONET; Componential aerosol optical depth;

Satellite remote sensing products of AOD from MODIS along with appropriate meteorological parameters were used to develop statistical models and estimate ground-level PM10. Most of previous studies obtained meteorological data from synoptic weather stations, with rather sparse spatial distribution, and used it along with 10 km AOD product to develop statistical models, applicable for PM variations in regional scale (resolution of ≥10 km). In the current study, meteorological parameters were simulated with 3 km resolution using WRF model and used along with the rather new 3 km AOD product (launched in 2014). The resulting PM statistical models were assessed for a polluted and largely variable urban area, Tehran, Iran. Despite the critical particulate pollution problem, very few PM studies were conducted in this area. The issue of rather poor direct PM-AOD associations existed, due to different factors such as variations in particles optical properties, in addition to bright background issue for satellite data, as the studied area located in the semi-arid areas of Middle East. Statistical approach of linear mixed effect (LME) was used, and three types of statistical models including single variable LME model (using AOD as independent variable) and multiple variables LME model by using meteorological data from two sources, WRF model and synoptic stations, were examined. Meteorological simulations were performed using a multiscale approach and creating an appropriate physic for the studied region, and the results showed rather good agreements with recordings of the synoptic stations. The single variable LME model was able to explain about 61%–73% of daily PM10 variations, reflecting a rather acceptable performance. Statistical models performance improved through using multivariable LME and incorporating meteorological data as auxiliary variables, particularly by using fine resolution outputs from WRF (R2 = 0.73–0.81). In addition, rather fine resolution for PM estimates was mapped for the studied city, and resulting concentration maps were consistent with PM recordings at the existing stations.Display Omitted
Keywords: PM10; AOD; MODIS; Mixed effects model; WRF;

Traffic contribution to air pollution in urban street canyons: Integrated application of the OSPM, moss biomonitoring and spectral analysis by Lazar Lazić; Mira Aničić Urošević; Zoran Mijić; Gordana Vuković; Luka Ilić (347-360).
To investigate the air pollutant distribution within the ambient of urban street canyon, Operational Street Pollution Model (OSPM) was used to predict hourly content of NOX, NO, NO2, O3, CO, BNZ and PM10. The study was performed in five street canyons in Belgrade (Serbia) during 10-week summer period. The model receptors were located on each side of street canyons at 4 m, 8 m and 16 m height.To monitor airborne trace element content, the moss bag biomonitors were simultaneously exposed with the model receptors at two heights–4 m and 16 m. The results of both methods, modelling and biomonitoring, showed significantly decreasing trend of the air pollutants with height. The results indirectly demonstrate that biomonitoring, i.e., moss bag technique could be a valuable tool to verify model performance.In addition, spectral analysis was applied to investigate weekly variation of the daily background and modelled data set. Typical periodicities and weekend effect, caused by anthropogenic influences, have been identified.
Keywords: Air pollution; Street canyons; The OSPM; Moss biomonitoring; Spectral analysis; Weekend effect;

Air pollutants degrade floral scents and increase insect foraging times by Jose D. Fuentes; Marcelo Chamecki; T’ai Roulston; Bicheng Chen; Kenneth R. Pratt (361-374).
Flowers emit mixtures of scents that mediate plant-insect interactions such as attracting insect pollinators. Because of their volatile nature, however, floral scents readily react with ozone, nitrate radical, and hydroxyl radical. The result of such reactions is the degradation and the chemical modification of scent plumes downwind of floral sources. Large Eddy Simulations (LES) are developed to investigate dispersion and chemical degradation and modification of floral scents due to reactions with ozone, hydroxyl radical, and nitrate radical within the atmospheric surface layer. Impacts on foraging insects are investigated by utilizing a random walk model to simulate insect search behavior. Results indicate that even moderate air pollutant levels (e.g., ozone mixing ratios greater than 60 parts per billion on a per volume basis, ppbv) substantially degrade floral volatiles and alter the chemical composition of released floral scents. As a result, insect success rates of locating plumes of floral scents were reduced and foraging times increased in polluted air masses due to considerable degradation and changes in the composition of floral scents. Results also indicate that plant-pollinator interactions could be sensitive to changes in floral scent composition, especially if insects are unable to adapt to the modified scentscape. The increase in foraging time could have severe cascading and pernicious impacts on the fitness of foraging insects by reducing the time devoted to other necessary tasks.
Keywords: Ozone; Hydroxyl radical; Pollination; Pollution; Hydrocarbons; Fragrances; Floral scents;

Elevated soil CO2 efflux at the boundaries between impervious surfaces and urban greenspaces by XiaoGang Wu; Dan Hu; ShengLi Ma; Xia Zhang; Zhen Guo; Kevin J. Gaston (375-378).
Impervious surfaces and greenspaces have significant impacts on ecological processes and ecosystem services in urban areas. However, there have been no systematic studies of how the interaction between the two forms of land cover, and especially their edge effects, influence ecosystem properties. This has made it difficult to evaluate the effectiveness of urban greenspace design in meeting environmental goals. In this study, we investigated edge effects on soil carbon dioxide (CO2) fluxes in Beijing and found that soil CO2 flux rates were averagely 73% higher 10 cm inwards from the edge of greenspaces. Distance, soil temperature, moisture, and their interaction significantly influenced soil CO2 flux rates. The magnitude and distance of edge effects differed among impervious structure types. Current greening policy and design should be adjusted to avoid the carbon sequestration service of greenspaces being limited by their fragmentation.
Keywords: Urban greenspace; Carbon; Soil; Edge effect; Impervious surface;

Real-world automotive particulate matter and PAH emission factors and profile concentrations: Results from an urban tunnel experiment in Naples, Italy by A. Riccio; E. Chianese; D. Monaco; M.A. Costagliola; G. Perretta; M.V. Prati; G. Agrillo; A. Esposito; D. Gasbarra; L. Shindler; G. Brusasca; A. Nanni; C. Pozzi; V. Magliulo (379-387).
On-road particulate matter (PM) mass was measured during a sampling campaign in March of 2015 in the ‘4 giornate’ tunnel in Naples, Italy. Two sets of samples were collected at both sides of the tunnel, each set representing the daily cycle at a 1 h time resolution. Distance-based – mass per kilometer – and fuel-based – mass per burned fuel – emission factors (EFs) were calculated using mass concentrations, traffic flow rates and wind speed as a function of fleet composition. Also, chemical analyses were performed for polycyclic aromatic hydrocarbons (PAHs).Due to the high traffic volume, particle mass concentration at the tunnel exit was always significantly elevated relative to entrance concentration; depending on the hour of the day, PM10 concentration ranged between 300 μg/m3, during the early afternoon, and 600 μg/m3 during rush hours at the tunnel exit. Correspondingly, PAHs achieved concentrations as high as 1450 ng/m3, and benzo(a)pyrene, a surely carcinogenic compound, achieved concentrations as high as 69 ng/m3, raising serious concerns in relation to population exposure close to this urban tunnel.Distance-based and fuel-based emission factors for CO2, PM10 and PAHs were estimated, but while the EF for CO2 was within the range of expected values, the present study found much higher EFs for particulate matter and PAHs. According to the national official statistics from ISPRA (the Italian Institute for the Protection and Research on Environment), derived from the COPERT database, we expected an EF for particulate matter of about 55 mg/km, but the EF estimated from measurements taken at both sides of the tunnel was about four times higher than that expected; also, benzo(a)pyrene achieved an average EF of 2.7 μg/km, about three times higher than that expected from the ISPRA database.
Keywords: Particulate matter; Particulate-bound PAH; On-road emission factors (EFs);

Satellite observations of ethylene (C2H4) from the Aura Tropospheric Emission Spectrometer: A scoping study by Wayana Dolan; Vivienne H. Payne; Susan S. Kualwik; Kevin W. Bowman (388-393).
We present a study focusing on detection and initial quantitative estimates of ethylene (C2H4) in observations from the Tropospheric Emission Spectrometer (TES), a Fourier transform spectrometer aboard the Aura satellite that measures thermal infrared radiances with high spectral resolution (0.1 cm−1). We analyze observations taken in support of the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission and demonstrate the feasibility of future development of C2H4 into a TES standard product. In the Northern Hemisphere, C2H4 is commonly associated with boreal fire plumes, motor vehicle exhaust and petrochemical emissions. It has a short lifetime (∼14–32 h) in the troposphere due to its reaction with OH and O3. Chemical destruction of C2H4 in the atmosphere leads to the production of ozone and other species such as carbon monoxide (CO) and formaldehyde. Results indicate a correlation between C2H4 and CO in boreal fire plumes. Quantitative C2H4 estimates are sensitive to assumptions about the plume height and width. We find that C2H4 greater than 2–3 ppbv can be detected in a single TES observation (for a fire plume at 3 km altitude and 1.5 km width). Spatial averaging will be needed for surface-peaking profiles where TES sensitivity is lower.
Keywords: Ethylene; Tropospheric Emission Spectrometer; Satellite remote sensing;

Assessment of regional influence from a petrochemical complex by modeling and fingerprint analysis of volatile organic compounds (VOCs) by Yuan-Chang Su; Sheng-Po Chen; Yu-Huei Tong; Chen-Lun Fan; Wei-Hao Chen; Jia-Lin Wang; Julius S. Chang (394-407).
This study aimed to demonstrate a strategy to investigate the influence of volatile organic compounds (VOCs) on its neighboring districts from a gigantic petrochemical complex. Monitoring of the VOCs in the region was achieved by a nine-station network, dubbed photochemical assessment measurement stations (PAMS), which produced speciated mixing ratios of 54 non-methane hydrocarbons (NMHCs) to represent VOCs with an hourly resolution within a 20 km radius. One-year (2013/10/1–2014/9/30) worth of PAMS data from the network were used in forms of total NMHCs (called PAMS-TNMHC) and speciated mixing ratios. Three dimensional modeling coupled with PAMS measurements successfully elucidated how the study domain was affected by the petrochemical complex and distant sources under three typical seasonal wind patterns: northeast monsoonal, southwest monsoonal, and local-circulation.More exquisite analysis of influence on the neighboring districts was permitted with the use of speciated mixing ratios of VOCs provided by the PAMS network. The ratios of ethylene/acetylene (E/A) > 3 and propylene/acetylene (P/A) > 1.5 were used as indicators to reveal the PAMS sites affected by the petrochemical emissions. Consequently, the hourly speciated data from the nine PAMS sites enabled a finer assessment of the districts affected by the complex to calculate the percent time of influence (dubbed TI%) for all the sites (districts). It was found that the region was more affected by the complex under both the northeast monsoonal and the local-circulation wind types with some of the PAMS sites greater than 5% for the TI%. By contrast, influence on the region was found minimal under the southwest monsoonal flow with the TI% small than 1.5% across all sites.This study successfully devised a method of assessment with the use of speciated measurements of selected VOCs and modeling to assess the influence of a prominent source on the neighboring districts by filtering out irrelevant sources under the complex meteorological conditions.
Keywords: Petrochemical industrial complex; Photochemical assessment measurement stations (PAMS); Fingerprint analysis;

Opportunistic mobile air pollution monitoring: A case study with city wardens in Antwerp by Joris Van den Bossche; Jan Theunis; Bart Elen; Jan Peters; Dick Botteldooren; Bernard De Baets (408-421).
The goal of this paper is to explore the potential of opportunistic mobile monitoring to map the exposure to air pollution in the urban environment at a high spatial resolution. Opportunistic mobile monitoring makes use of existing mobile infrastructure or people’s common daily routines to move measurement devices around. Opportunistic mobile monitoring can also play a crucial role in participatory monitoring campaigns as a typical way to gather data.A case study to measure black carbon was set up in Antwerp, Belgium, with the collaboration of city employees (city wardens). The Antwerp city wardens are outdoors for a large part of the day on surveillance tours by bicycle or on foot, and gathered a total of 393 h of measurements. The data collection is unstructured both in space and time, leading to sampling bias. A temporal adjustment can only partly counteract this bias. Although a high spatial coverage was obtained, there is still a rather large uncertainty on the average concentration levels at a spatial resolution of 50 m due to a limited number of measurements and sampling bias. Despite of this uncertainty, large spatial patterns within the city are clearly captured.This study illustrates the potential of campaigns with unstructured opportunistic mobile monitoring, including participatory monitoring campaigns. The results demonstrate that such an approach can indeed be used to identify broad spatial trends over a wider area, enabling applications including hotspot identification, personal exposure studies, regression mapping, etc. But, they also emphasize the need for repeated measurements and careful processing and interpretation of the data.Display Omitted
Keywords: Opportunistic monitoring; Mobile measurements; Black carbon; Urban air quality; Spatial variation;

A simple urban air quality model [MODelo de Dispersión Atmosférica Ubana – Generic Reaction Set (DAUMOD-GRS)] was recently developed. One-hour peak O3 concentrations in the Metropolitan Area of Buenos Aires (MABA) during the summer estimated with the DAUMOD-GRS model have shown values lower than 20 ppb (the regional background concentration) in the urban area and levels greater than 40 ppb in its surroundings. Due to the lack of measurements outside the MABA, these relatively high ozone modelled concentrations constitute the only estimate for the area. In this work, a methodology based on the Monte Carlo analysis is implemented to evaluate the uncertainty in these modelled concentrations associated to possible errors of the model input data. Results show that the larger 1-h peak O3 levels in the MABA during the summer present larger uncertainties (up to 47 ppb). On the other hand, multiple linear regression analysis is applied at selected receptors in order to identify the variables explaining most of the obtained variance. Although their relative contributions vary spatially, the uncertainty of the regional background O3 concentration dominates at all the analysed receptors (34.4–97.6%), indicating that their estimations could be improved to enhance the ability of the model to simulate peak O3 concentrations in the MABA.
Keywords: Air quality; Model uncertainty; Sensitivity; Ozone; Monte Carlo analysis;

In this study, the sorptive loss properties of biogenic volatile organic compounds (BVOCs) in polyester aluminum bags were investigated as a function of storage duration. To this end, the relative recovery of gas phase standards of BVOCs, obtained via vaporization of liquid phase standards, was computed by calibrating their standards (response factors: RF) represnting each phase. Accordingly, the results indicated either slight loss (−5.59% (isoprene), −2.39% (camphene), −1.69% ((R)-(+)-limonene), −0.88% (p-cymene)) or gain (1.47% (γ-terpinene), 2.27% (α-terpinene), 2.63% (α-phellandrene), 2.73% ((+)-3-carene), 3.93% ((+)-β-pinene), and 5.98% ((+)-α-pinene)). Through comparison of the calibration results across storage time, the temporal stability of BVOCs was assessed. Longer BVOC storage time in polyester aluminum (PEA) bags lowered the relative recovery of BVOCs. The relative loss of BVOCs, if calculated in terms of mean bag standard RF ratios (relative to liquid standard) across elapsed time, decreased systematically: 0.99 ± 0.05 (0 h), 0.88 ± 0.06 (24 h), 0.66 ± 0.11 (72 h), and 0.62 ± 0.14 (120 h). It is thus recommended to complete the analysis of BVOC in PEA bags within 24 h of sample acquisition. As such, it is important to apply appropriate sampling approaches with a proper storage plan when measuring ambient BVOCs collected by bag sampling methods.
Keywords: Biogenic volatile organic compounds (BVOC); GC/MS; Polyester aluminum bags; Relative recovery; Storage stability;

Joint measurements of black carbon and particle mass for heavy-duty diesel vehicles using a portable emission measurement system by Xuan Zheng; Ye Wu; Shaojun Zhang; Richard W. Baldauf; K. Max Zhang; Jingnan Hu; Zhenhua Li; Lixin Fu; Jiming Hao (435-442).
The black carbon (BC) emitted from heavy-duty diesel vehicles (HDDVs) is an important source of urban atmospheric pollution and creates strong climate-forcing impacts. The emission ratio of BC to total particle mass (PM) (i.e., BC/PM ratio) is an essential variable used to estimate total BC emissions from historical PM data; however, these ratios have not been measured using portable emission measurement systems (PEMS) in order to obtain real-world measurements over a wide range of driving conditions. In this study, we developed a PEMS platform by integrating two Aethalometers and an electric low pressure impactor to realize the joint measurement of real-world BC and PM emissions for ten HDDVs in China. Test results showed that the average BC/PM ratio for five HDDVs equipped with mechanical fuel injection (MI) engines was 0.43 ± 0.06, significantly lower (P < 0.05) than another five HDDVs equipped with electronically-controlled fuel injection (EI) engines (0.56 ± 0.12). Traffic conditions also affected the BC/PM ratios with higher ratios on freeway routes than on local roads. Furthermore, higher ratios were observed for HDDVs equipped with EI engines than for the MI engines for the highway and local road routes. With an operating mode binning approach, we observed that the instantaneous BC/PM ratios of EI engine vehicles were above those of the MI engine vehicles in all operating modes except for the braking mode (i.e., Bin 0). Therefore, the complex impacts from engine technology and traffic conditions on BC/PM ratios should be carefully considered when estimating real-world BC emissions from HDDVs based on overall PM emissions data.
Keywords: Portable emission measurement system; Real-world emission; Heavy-duty diesel vehicle; Black carbon; Particle mass;

Temporal and spatial variations of particulate matter and gaseous pollutants in the urban area of Tehran by O. Alizadeh-Choobari; A.A. Bidokhti; P. Ghafarian; M.S. Najafi (443-453).
Being hemmed in on two sides by high mountains, the urban area of Tehran is characterized by high levels of particulate matter and gaseous pollutants, which have adverse consequences on human health, ecosystems and environment. Using air quality measurements taken in different regions of Tehran, spatial and temporal variations of particulate matter and gaseous pollutants are analyzed to identify the typical climatological aspects of air pollutants. In terms of particulate matter concentrations, South Tehran is more polluted than Central to North Tehran, while West Tehran is more polluted than the East. Concentrations of particles in North Tehran are lower in the midday compared to the midnight, whereas the opposite is true in South Tehran. The observed annual mean concentrations of PM2.5 and PM10 in North Tehran were 37.5 and 76.3 μg m−3, respectively, which are substantially greater than the national annual mean safety limits of 10 μg m−3 for PM2.5 and 20 μg m−3 for PM10. The observed high levels of particulate matter underline the essential need for a coordinated action to reduce the rapidly increasing air pollution over the growing urban area of Tehran. Noticeable monthly (seasonal) variations are evident in the observed PM10 concentrations, with a minimum of 61.5 μg m−3 in March (spring) and a maximum of 82.9 μg m−3 in July (summer), reflecting contribution of weather conditions. Analyzing daily PM2.5 (PM10) concentrations indicate that mid-week Wednesdays (Mondays) are the most polluted days. The higher mid-week concentrations reflect contribution of heavy vehicular traffic, industrial operation and increased commercial activities. Strong diurnal variations in the concentrations of particulate matter in North Tehran are detected, varying from a peak in late night to a minimum in late afternoon, indicating contribution of deeper daytime convective boundary layer and stronger winds in dispersion of particles.
Keywords: Air quality; Particulate matter; Gaseous pollutants; Air pollution; Boundary layer; Tehran;

Ozone concentrations in air flowing into New York State by Nenad Aleksic; John Kent; Chris Walcek (454-461).
Ozone (O3) concentrations measured at Pinnacle State Park (PSPNY), very close to the southern border of New York State, are used to estimate concentrations in air flowing into New York. On 20% of the ozone season (April–September) afternoons from 2004 to 2015, mid-afternoon 500-m back trajectories calculated from PSPNY cross New York border from the south and spend less than three hours in New York State, in this area of negligible local pollution emissions. One-hour (2p.m.–3p.m.) O3 concentrations during these inflowing conditions were 46 ± 13 ppb, and ranged from a minimum of 15 ppb to a maximum of 84 ppb. On average during 2004–2015, each year experienced 11.8 days with inflowing 1-hr O3 concentrations exceeding 50 ppb, 4.3 days with O3 > 60 ppb, and 1.5 days had O3 > 70 ppb. During the same period, 8-hr average concentrations (10a.m. to 6p.m.) exceeded 50 ppb on 10.0 days per season, while 3.9 days exceeded 60 ppb, and 70 ppb was exceeded 1.2 days per season. Two afternoons of minimal in-state emission influences with high ozone concentrations were analyzed in more detail. Synoptic and back trajectory analysis, including comparison with upwind ozone concentrations, indicated that the two periods were characterized as photo-chemically aged air containing high inflowing O3 concentrations most likely heavily influenced by pollution emissions from states upwind of New York including Pennsylvania, Tennessee, West Virginia, and Ohio. These results suggest that New York state-level attempts to comply with National Ambient Air Quality Standards by regulating in-state O3 precursor NOx and organic emissions would be very difficult, since air frequently enters New York State very close to or in excess of Federal Air Quality Standards.
Keywords: Regional ozone transport; Background ozone; Ozone standards;

Modeling the impact of solid noise barriers on near road air quality by Akula Venkatram; Vlad Isakov; Parikshit Deshmukh; Richard Baldauf (462-469).
Studies based on field measurements, wind tunnel experiments, and controlled tracer gas releases indicate that solid, roadside noise barriers can lead to reductions in downwind near-road air pollutant concentrations. A tracer gas study showed that a solid barrier reduced pollutant concentrations as much as 80% next to the barrier relative to an open area under unstable meteorological conditions, which corresponds to typical daytime conditions when residents living or children going to school near roadways are most likely to be exposed to traffic emissions. The data from this tracer gas study and a wind tunnel simulation were used to develop a model to describe dispersion of traffic emissions near a highway in the presence of a solid noise barrier. The model is used to interpret real-world data collected during a field study conducted in a complex urban environment next to a large highway in Phoenix, Arizona, USA. We show that the analysis of the data with the model yields useful information on the emission factors and the mitigation impact of the barrier on near-road air quality. The estimated emission factors for the four species, ultrafine particles, CO, NO2, and black carbon, are consistent with data cited in the literature. The results suggest that the model accounted for reductions in pollutant concentrations from a 4.5 m high noise barrier, ranging from 40% next to the barrier to 10% at 300 m from the barrier.
Keywords: Air quality; Dispersion model; Noise barrier; Field data; Emission factors;

An exceptional particulate pollution event was sampled in June 2005 over the Ardèche region in Southern France. Airborne (at the wavelength of 355 nm) and ground-based (at the wavelength of 532 nm) lidars performed measurements simultaneously. Airborne observations were performed from an ultra-light aircraft (ULA); they offer an opportunity to test a new method for inversing lidar profiles which enables their quantitative use while the airplane flies in a scattering layer. Using the results of this approach and the ground-based lidar measurements, the aerosol plumes have been optically quantified and the diversity of particle sources (from Western Europe, North Africa and even North America) which contributed to the event has been highlighted using both spaceborne observations and multiple air mass back-trajectories.
Keywords: Aerosol; Optical properties; Pollution; Airborne lidar; Ultra-light aircraft;

The western Mediterranean basin as an aged aerosols reservoir. Insights from an old-fashioned but efficient radiotracer by E. Brattich; M.A. Hernández-Ceballos; J.A.G. Orza; J.P. Bolívar; L. Tositti (481-493).
The long-term contemporary 210Pb time series acquired during the period 2004–2011 at two distant sites of different altitude in the Mediterranean basin, El Arenosillo (40 m a.s.l. in southwestern Spain) and Mt. Cimone (2165 m a.s.l. in northern Italy), are analyzed and compared. Besides being considered a tracer of continental air masses, 210Pb radionuclide is also a proxy of fine stable aerosol. For this reason, the measurements of PM10 mass concentrations collected at the same time and the corresponding 210Pb/PM10 ratio at the two sites are considered to gain better insights into the origin and size of the particles.Three statistical trajectory methods are applied to identify and characterize the 210Pb source regions at the two sites. The three methods yield similar outcomes in the source identification, which strengthens the robustness of our results. In addition to the importance of the transport from areas of continental Europe, this study highlights the relevant role of the Mediterranean Sea as a major 210Pb reservoir layer associated to the aged air masses that accumulate in the western Mediterranean basin. The analysis of the sources points out the significant influence of northern Africa to 210Pb increases at both sites as well, even though the most intensive episodes are not of Saharan origin.
Keywords: 210Pb; PM10; Radiotracer; Source identification; Residence time; PSCF; Mediterranean basin; Saharan dust;

Effect of hygroscopic growth on the aerosol light-scattering coefficient: A review of measurements, techniques and error sources by G. Titos; A. Cazorla; P. Zieger; E. Andrews; H. Lyamani; M.J. Granados-Muñoz; F.J. Olmo; L. Alados-Arboledas (494-507).
Knowledge of the scattering enhancement factor, f(RH), is important for an accurate description of direct aerosol radiative forcing. This factor is defined as the ratio between the scattering coefficient at enhanced relative humidity, RH, to a reference (dry) scattering coefficient. Here, we review the different experimental designs used to measure the scattering coefficient at dry and humidified conditions as well as the procedures followed to analyze the measurements. Several empirical parameterizations for the relationship between f(RH) and RH have been proposed in the literature. These parameterizations have been reviewed and tested using experimental data representative of different hygroscopic growth behavior and a new parameterization is presented. The potential sources of error in f(RH) are discussed. A Monte Carlo method is used to investigate the overall measurement uncertainty, which is found to be around 20–40% for moderately hygroscopic aerosols. The main factors contributing to this uncertainty are the uncertainty in RH measurement, the dry reference state and the nephelometer uncertainty. A literature survey of nephelometry-based f(RH) measurements is presented as a function of aerosol type. In general, the highest f(RH) values were measured in clean marine environments, with pollution having a major influence on f(RH). Dust aerosol tended to have the lowest reported hygroscopicity of any of the aerosol types studied. Major open questions and suggestions for future research priorities are outlined.
Keywords: Scattering enhancement; Water uptake; Hygroscopicity; Aerosol light scattering;

Road salt emissions: A comparison of measurements and modelling using the NORTRIP road dust emission model by B.R. Denby; M. Ketzel; T. Ellermann; A. Stojiljkovic; K. Kupiainen; J.V. Niemi; M. Norman; C. Johansson; M. Gustafsson; G. Blomqvist; S. Janhäll; I. Sundvor (508-522).
De-icing of road surfaces is necessary in many countries during winter to improve vehicle traction. Large amounts of salt, most often sodium chloride, are applied every year. Most of this salt is removed through drainage or traffic spray processes but a certain amount may be suspended, after drying of the road surface, into the air and will contribute to the concentration of particulate matter. Though some measurements of salt concentrations are available near roads, the link between road maintenance salting activities and observed concentrations of salt in ambient air is yet to be quantified. In this study the NORTRIP road dust emission model, which estimates the emissions of both dust and salt from the road surface, is applied at five sites in four Nordic countries for ten separate winter periods where daily mean ambient air measurements of salt concentrations are available. The model is capable of reproducing many of the salt emission episodes, both in time and intensity, but also fails on other occasions. The observed mean concentration of salt in PM10, over all ten datasets, is 4.2 μg/m3 and the modelled mean is 2.8 μg/m3, giving a fractional bias of −0.38. The RMSE of the mean concentrations, over all 10 datasets, is 2.9 μg/m3 with an average R2 of 0.28. The mean concentration of salt is similar to the mean exhaust contribution during the winter periods of 2.6 μg/m3. The contribution of salt to the kerbside winter mean PM10 concentration is estimated to increase by 4.1 ± 3.4 μg/m3 for every kg/m2 of salt applied on the road surface during the winter season. Additional sensitivity studies showed that the accurate logging of salt applications is a prerequisite for predicting salt emissions, as well as good quality data on precipitation. It also highlights the need for more simultaneous measurements of salt loading together with ambient air concentrations to help improve model parameterisations of salt and moisture removal processes.
Keywords: Road salt; Non-exhaust emissions; Air quality; Particulate matter; Modelling;

Estimation of indoor and outdoor ratios of selected volatile organic compounds in Canada by Jing Xu; Mieczyslaw Szyszkowicz; Branka Jovic; Sabit Cakmak; Claire C. Austin; Jiping Zhu (523-531).
Indoor air and outdoor air concentration (I/O) ratio can be used to identify the origins of volatile organic compounds (VOCs). I/O ratios of 25 VOCs in Canada were estimated based on the data collected in various areas in Canada between September 2009 and December 2011. The indoor VOC data were extracted from the Canadian Health Measures Survey (CHMS). Outdoor VOC data were obtained from Canada's National Air Pollution Surveillance (NAPS) Network. The sampling locations covered nine areas in six provinces in Canada. Indoor air concentrations were found higher than outdoor air for all studied VOCs, except for carbon tetrachloride. Two different approaches were employed to estimate the I/O ratios; both approaches produced similar I/O values. The I/O ratios obtained from this study were similar to two other Canadian studies where indoor air and outdoor air of individual dwellings were measured. However, the I/O ratios found in Canada were higher than those in European cities and in two large USA cities, possibly due to the fact that the outdoor air concentrations recorded in the Canadian studies were lower. Possible source origins identified for the studied VOCs based on their I/O ratios were similar to those reported by others. In general, chlorinated hydrocarbons, short-chain (C5, C6) n-alkanes and benzene had significant outdoor sources, while long-chain (C10―C12) n-alkanes, terpenes, naphthalene and styrene had significant indoor sources. The remaining VOCs had mixed indoor and outdoor sources.
Keywords: Indoor air; Outdoor air; I/O ratio; Volatile organic compounds; Source origin;

Aerosol types and radiative forcing estimates over East Asia by Rohini L. Bhawar; Woo-Seop Lee; P.R.C. Rahul (532-541).
Using the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data sets along with the CSIRO-MK 3.6.0 model simulations, we analyzed the aerosol optical depth (AOD) variability during March–May (MAM), June–August (JJA) along with their annual mean variability over East Asia for the period 2006–2012. The CALIPSO measurements correlated well with the MODIS measurements and the CSIRO-MK 3.6.0 model simulations over the spatial distribution patterns of the aerosols, but CALIPSO underestimated the magnitudes of the AOD. Maximum smoke aerosol loading is observed to occur during JJA, as a result of wind transport from Southern China while dust loading dominated during MAM via the transport from desert region. The vertical distribution profiles revealed that there is uniform distribution of smoke aerosols during both MAM and JJA, only differing at the altitude at which they peak; while the dust aerosols during MAM showed a significant distribution from the surface to 10 km altitude and JJA was marked with lower dust loading at the same altitudes. Both dust and smoke aerosols warm the atmosphere in MAM but due to the absorbing nature of smoke aerosols, they cause considerable cooling at the surface which is double when compared to the dust aerosols. The top of the atmosphere aerosol radiative forcing (ARF) due to smoke and dust aerosols is positive in MAM which indicates warming over East Asia. During MAM a consistent declining trend of the surface ARF due to smoke aerosols persisted over the last three decades as conspicuously evidenced from model analysis; the decline is ∼10 W/m2 from 1980 to 2012.
Keywords: Radiative forcing; CALIPSO; Smoke; Vertical profile;

Implications of diesel emissions control failures to emission factors and road transport NOx evolution by Leonidas Ntziachristos; Giannis Papadimitriou; Norbert Ligterink; Stefan Hausberger (542-551).
Diesel NOx emissions have been at the forefront of research and regulation scrutiny as a result of failures of late vehicle technologies to deliver on-road emissions reductions. The current study aims at identifying the actual emissions levels of late light duty vehicle technologies, including Euro 5 and Euro 6 ones. Mean NOx emission factor levels used in the most popular EU vehicle emission models (COPERT, HBEFA and VERSIT+) are compared with latest emission information collected in the laboratory over real-world driving cycles and on the road using portable emissions measurement systems (PEMS). The comparison shows that Euro 5 passenger car (PC) emission factors well reflect on road levels and that recently revealed emissions control failures do not call for any significant corrections. However Euro 5 light commercial vehicles (LCVs) and Euro 6 PCs in the 2014–2016 period exhibit on road emission levels twice as high as used in current models. Moreover, measured levels vary a lot for Euro 6 vehicles. Scenarios for future evolution of Euro 6 emission factors, reflecting different degree of effectiveness of emissions control regulations, show that total NOx emissions from diesel Euro 6 PC and LCV may correspond from 49% up to 83% of total road transport emissions in 2050. Unless upcoming and long term regulations make sure that light duty diesel NOx emissions are effectively addressed, this will have significant implications in meeting future air quality and national emissions ceilings targets.
Keywords: Diesel light duty vehicles; NOx emissions; EFs; Emission control technologies; COPERT; HBEFA; VERSIT;

The heterogeneous oxidation of sulfur dioxide (SO2) on α-Al2O3 particles was investigated using a flow reactor coupled with a transmission-Fourier transform infrared (T-FTIR) spectrometer at different relative humidities (RH) in the absence or presence of hydrogen peroxide (H2O2), with an emphasis on the saturation coverage of SO2 and the timescale on which the reaction reaches saturation. It is found that the saturation coverage of SO2 in the absence of H2O2 increases with rising RH due to the hydrolysis of SO2 by surface adsorbed water. However, the reaction ultimately reaches saturation since the produced sulfite/bisulfite cannot be further converted to sulfate/bisulfate in the absence of oxidants. In addition, the presence of H2O2 can significantly increase the saturation coverage of SO2 by efficiently oxidizing sulfite/bisulfite to sulfate/bisulfate. Under humid conditions, adsorbed water facilitates the hydrolysis of SO2 and mitigates the increase of surface acidity, which can inhibit the hydrolysis of SO2. Hence, in the presence of H2O2, the saturation coverage of SO2 as well as the time of reaction reaching saturation increases with rising RH and the surface is not saturated on the timescale of the experiments (40 h) at 60% RH. Furthermore, the increase of saturation coverage of SO2 in the presence of H2O2 was observed on chemically inactive SiO2 particles, indicating that the hydrolysis of SO2 and subsequent oxidation by H2O2 likely occurs on other types of particles. Our findings are of importance for understanding the role of water vapor and trace gases (e.g., H2O2) in the heterogeneous reaction of SO2 in the atmosphere.
Keywords: Heterogeneous reaction; Sulfur dioxide; Hydrogen peroxide; Saturation coverage;

VOC characteristics, emissions and contributions to SOA formation during hazy episodes by Jie Sun; Fangkun Wu; Bo Hu; Guiqian Tang; Junke Zhang; Yuesi Wang (560-570).
Volatile organic compounds (VOC) are important precursors of secondary organic aerosols (SOA). The pollution processes in Beijing were investigated from 18th October to 6th November 2013 to study the characteristics, SOA formation potential and contributing factors of VOC during hazy episodes. The mean concentrations of VOC were 67.4 ± 33.3 μg m−3 on clear days and have 5–7-fold increase in polluted periods. VOC concentrations rapidly increased at a visibility range of 4–5 km with the rate of 25%/km in alkanes, alkenes and halocarbons and the rate of 45%/km in aromatics. Analysis of the mixing layer height (MLH); wind speed and ratios of benzene/toluene (B/T), ethylbenzene/m,p-xylene (E/X), and isopentane/n-pentane (i/n) under different visibility conditions revealed that the MLH and wind speed were the 2 major factors affecting the variability of VOC during clear days and that local emissions and photochemical reactions were main causes of VOC variation on polluted days. Combined with the fractional aerosol coefficient (FAC) method, the SOA formation potentials of alkanes, alkenes and aromatics were 0.3 ± 0.2 μg m−3, 1.1 ± 1.0 μg m−3 and 6.5 ± 6.4 μg m−3, respectively. As the visibility deteriorated, the SOA formation potential increased from 2.1 μg m−3 to 13.2 μg m−3, and the fraction of SOA-forming aromatics rapidly increased from 56.3% to 90.1%. Initial sources were resolved by a positive matrix factorization (PMF) model. Vehicle-related emissions were an important source of VOC at all visibility ranges, accounting for 23%–32%. As visibility declined, emissions from solvents and the chemical industry increased from 13.2% and 6.3% to 34.2% and 23.0%, respectively. Solvents had the greatest SOA formation ability, accounting for 52.5% on average on hazy days, followed by vehicle-related emissions (20.7%).
Keywords: VOC; Haze; SOA formation potential; Initial emission sources;

Role of the boundary layer dynamics effects on an extreme air pollution event in Paris by J.-C. Dupont; M. Haeffelin; J. Badosa; T. Elias; O. Favez; J.E. Petit; F. Meleux; J. Sciare; V. Crenn; J.L. Bonne (571-579).
The physical and chemical aerosol properties are explored here based on ground-based observations in the Paris region to better understand the role of clouds, radiative fluxes and dynamics on aerosol loading during a heavy regional air pollution that occurred in March 2014 over North-Western Europe. This event is primarily characterized by a fine particle mass (PM2.5) increase from 10 to more than 120 μg m−3 and a simultaneous decrease of the horizontal visibility from 40 to 1 km, mainly due to significant formation of ammonium nitrate particles. The aerosol optical depth (AOD) at 550 nm increased steadily from about 0.06 on March 6 to more than 0.9 five days later. The scattering of the solar radiation by polluted particles induced, at the peak of the heavy pollution event, an instantaneous shortwave flux decrease of about 300 W m−2 for direct irradiance and an increase of about 150 W m−2 for diffuse irradiance (only scattering). The mean surface aerosol effect efficiency (effect per unit optical depth) is of about −80 W m−2 with a mean aerosol direct radiative effect of −23 W m−2. The dynamical and radiative processes that can be responsible for the diurnal cycle of PM2.5 in terms of amplitude and timing are investigated. A comparative analysis is performed for 4 consecutive days (between March 11 and 14), showing that the PM2.5 diurnal cycle can be modulated in time and amplitude by local processes such as the boundary layer depth development (ranging from 100 m to 1350 m), surface relative humidity (100%–35%), thermal structure (10 °C–16 °C for day/night amplitude), dynamics (wind speed ranging from 4 m s−1 to 1.5 m s−1) and turbulence (turbulent kinetic energy reaching 2 m2 s−2) near the surface and wind shear along the vertical. Finally, modeled and measured surface PM2.5 loadings are also compared here, notably illustrating the need of accurate boundary layer depth data for efficient air quality forecasts.
Keywords: Pollution; Dynamics; Boundary layer depth;