Atmospheric Environment (v.123, #PA)

To mitigate NOx and other emissions from diesel vehicles, China I, China II, China III and China IV emissions standards for new vehicles have been implemented nationwide. However, recent on-road measurements using a portable emission measurement system (PEMS) have revealed no significant reductions in the NOx emissions factors of diesel trucks due to the change from China II emissions standards to the more stringent China III standards. Thus, it is important to understand the effect of the China IV emissions standard on NOx emissions. In this study, nine China III and nine China IV diesel trucks of three sizes (light-duty diesel trucks (LDDTs), medium-duty diesel trucks (MDDTs) and heavy-duty diesel trucks (HDDTs)) were tested on real roads in Beijing using a PEMS. Compared to the tested China III diesel trucks, the China IV diesel trucks showed significant reductions of the average NOx emissions factors in terms of both distance travelled and fuel consumption. However, the driving conditions had an important impact on the reduction. Under non-highway driving (NHD), several of the tested China IV diesel trucks experienced no reduction or an increase in NOx emissions compared to their China III counterparts. The NOx emissions factors of the 18 tested diesel trucks under NHD were on average 1.5-times greater than those under highway driving (HD), and the effects on NOx emissions removal from China III to China IV diesel trucks were greater under HD than under NHD. In addition, no significant reduction of NOx based on fuel consumption for China IV diesel trucks was observed for MDDTs and HDDTs compared to the test results for similar China II vehicles reported in a previous study. To reduce NOx emissions in China, additional control measures of vehicular NOx emissions should be formulated.
Keywords: Emissions factor; Nitrogen oxides; Diesel vehicle; Vehicle emissions standard; PEMS; Beijing;

Surface greenhouse gas fluxes downwind of a penguin colony in the maritime sub-Antarctic by Julia Drewer; Christine F. Braban; Y. Sim Tang; Margaret Anderson; Ute M. Skiba; Ulrike Dragosits; Phil Trathan (9-17).
The relationship between ammonia (NH3) concentrations downwind from a penguin colony and local surface greenhouse gas (GHG) fluxes was investigated on the remote sub-Antarctic Bird Island (54°00′S, 38°03′W) during summer 2010 (November and December). A Macaroni penguin (Eudyptes chrysolophus) colony (40,000 pairs) at Goldcrest Point is a large point source of NH3 on the island and a measurement transect of 23 m, 36 m, 70 m, 143 m and 338 m was set up downwind from the colony. Atmospheric NH3 concentrations measured by passive diffusion samplers declined from 23 μg m−3 close to the colony to less than 1 μg m−3 338 m downwind. As increased nitrogen (N) deposition can affect soil carbon (C) and N cycling, it can therefore potentially influence GHG and nitric oxide (NO) emission rates. However, in this study, a clear correlation between surface GHG fluxes and atmospheric NH3 concentrations could not be established. Average fluxes for nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) over the entire transect and the eight week study period ranged from 7 to 23 μg N2O–N m−2 h−1, −5.5–245 μg CH4 m−2 h−1, and CO2 respiration rates averaged 2.2 μmol m−2 s−1. Laboratory studies using intact soil cores from the transect also did not show any significant correlation between atmospheric NH3 concentrations and N2O, NO, CH4 emissions or CO2 respiration rates. Overall, fluxes measured in the laboratory study reflected the high variability measured in the field. Large changes in soil depth along the transect, due to the topography of the island, possibly influenced fluxes more than NH3 concentration and seabirds appeared to have a more localised input (e.g. ground nesting birds). However, warmer temperatures might have a large potential to increase GHG fluxes in this ecosystem. This study confirms that GHG fluxes do occur in these ornithogenic ecosystems, however, the scale of the impact remains largely unquantified due to high uncertainties and high spatial variability.
Keywords: Methane; Nitrous oxide; Carbon dioxide; Nitric oxide; Sub-Antarctica; Vegetal residue;

We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and major ions as well as stable carbon and nitrogen isotope ratios (δ13C and δ15N) in ambient aerosols at a suburban site (Mangshan), 40 km north of Beijing, China. We found that aerosol chemical compositions were largely controlled by the air mass transport from Beijing in daytime with southerly winds and by relatively fresh air mass in nighttime from the northern forest areas with northerly winds. Higher concentrations of aerosol mass and total carbon were obtained in daytime. Further, higher OC/EC ratios were recorded in daytime (4.0 ± 1.7) than nighttime (3.2 ± 0.7), suggesting that OC is formed by photochemical oxidation of gaseous precursors in daytime. Contributions of WSOC to OC were slightly higher in daytime (38%) than nighttime (34%), possibly due to secondary formation of WSOC in daytime. We also found higher concentrations of Ca2+ in daytime, which was originated from the construction dust in Beijing area and transported to the sampling site. δ13C ranged from −25.3 to −21.2‰ (ave. −23.5 ± 0.9‰) in daytime and −29.0 to −21.4‰ (−24.0 ± 1.5‰) in nighttime, suggesting that Mangshan aerosols were more influenced by fossil fuel combustion products in daytime and by terrestrial C3 plants in nighttime. This study suggests that daytime air mass delivery from megacity Beijing largely influence the air quality at the receptor site in the north together with photochemical processing of organic aerosols during the atmospheric transport, whereas the Mangshan site is covered with relatively clean air masses at night.
Keywords: Aerosols; Inorganic ions; Organic carbon; Elemental carbon; Isotope ratios;

Estimation of zone of influences (ZoI) at signalised traffic intersections (TI) is important to accurately model particle number concentrations (PNCs) and their exposure to public at emission hotspot locations. However, estimates of ZoI for PNCs at different types of TIs are barely known. We carried out mobile measurements inside the car cabin with windows fully open for size–resolved PNCs in the 5–560 nm range on a 6 km long busy round route that had 10 TIs. These included four–way TIs without built–up area (TI4w-nb), four–way TIs with built–up area (TI4w-wb), three–way TIs without built–up area (TI3w-nb) and three–way TIs with built–up area (TI3w-wb). Mobile measurements were made with a fast response differential mobility spectrometer (DMS50). Driving speed and position of the car were recorded every second using a global positioning system (GPS). Positive matrix factorisation (PMF) modelling was applied on the data to quantify the contribution of PNCs released during deceleration, creep–idling, acceleration and cruising to total PNCs at the TIs. The objectives were to address the following questions: (i) how does ZoI vary at different types of TIs in stop– and go–driving conditions?, (ii) what is the effect of different driving conditions on ZoI of a TI?, (iii) how realistically can the PNC profiles be generalised within a ZoI of a TI?, and (iv) what is the share of emissions during different driving conditions towards the total PNCs at a TI? Average length of ZoI in longitudinal direction and along the road was found to be the highest (148 m; 89 to −59 m from the centre of a TI) at a TI3w-wb, followed by TI4w-nb (129 m; 79 to −42 m), TI3w-nb (86 m; 71 to −15 m) and TI4w-wb (79 m; 46 to −33 m) in stop– and go–driving conditions. During multiple stopping driving conditions when a vehicle stops at a TI more than once in a signal cycle due to oversaturation of vehicles, average length of ZoI increased by 55, 22 and 21% at TI4w-nb, TI3w-nb and TI3w-wb, respectively, compared with stop– and go–driving conditions. Within average length of ZoI in stop– and go– driving conditions, PNCs followed a three degree polynomial form at all TIs. Dimensional analysis suggested that coefficients of polynomial equations at both four–way and three–way TIs were mainly influenced by delay time, wind speed and particle number flux. The PMF analysis suggested that deceleration contributed the most to total PNCs at all TIs, except TI4w-wb. Findings of this study are a step forward to understand the contribution of different driving conditions towards the total PNCs and their exposure at the TIs.Display Omitted
Keywords: Number size distribution; Traffic intersection; PNC profile; Driving condition; Positive matrix factorisation;

On the concentration and size distribution of sub-micron aerosol in the Galápagos Islands by M. Sorribas; J.C. Gómez Martín; T.D. Hay; A.S. Mahajan; C.A. Cuevas; M.V. Agama Reyes; F. Paredes Mora; M. Gil-Ojeda; A. Saiz-Lopez (39-48).
During the CHARLEX campaign in the Galápagos Islands, a Scanning Particle Mobility Sizer was deployed on San Cristobal Island in July–August 2011 to carry out size-resolved measurements of the concentration of submicron aerosols. To our knowledge these are the first measurements of aerosol concentrations in this unique environment. The particles with marine origin displayed a tri-modal number size distribution with peak diameters of 0.016 μm, 0.050 μm and 0.174 μm and a cloud-processed intermodal minimum at 0.093 μm. The mean total aerosol number concentration for the marine contribution was 470 ± 160 cm−3. A low particle concentration of 70 ± 50 cm−3 for the nucleation size range was measured, but no evidence of new particle production in the atmospheric marine boundary layer (MBL) was observed. The concentration of the Aitken size mode was found to be related to aerosol entrainment from the free troposphere off the coast of Chile followed by transport within the MBL to the Galápagos Islands. Cloud processing may activate the particles in the Aitken size range, growing through ‘in-cloud’ sulphate production and increasing the particle concentration in the accumulation size range. The 0.093 μm cloud processed minima suggests that the critical supersaturation at which the particle is activated to a cloud droplet is in the 0.14–0.21% range. The daytime marine particle background concentration was influenced by human activity around the sampling site, as well as by new particle formation triggered by biogenic emissions from the vegetation cover of the island's semiarid lowlands. Effective CCN formation may play a role in the formation and properties of the stratus clouds, which permanently cover the top of the windward side of the islands and establish one of their characteristic climatic bands.
Keywords: Sub-micrometre particle; SMPS; Marine boundary layer;

Multiple approaches to characterize lateral boundary contributions to photochemical model predicted ozone (O3) and particulate matter less than 2.5 microns in diameter (PM2.5) are available in the Comprehensive Air quality Model with extensions (CAMx). Here, three approaches are used for O3: (1) a comprehensive source apportionment scheme for chemical boundary conditions and emissions (OSAT), (2) chemically reactive tracers (RTRAC), and (3) chemically inert tracers. Two approaches are used for PM2.5: (1) particulate source apportionment (PSAT) and (2) chemically inert tracers. The inert tracer approach resulted in higher O3 lateral boundary contribution estimates because the method does not account for any O3 destruction reactions. OSAT and RTRAC estimate generally similar monthly average contributions during the warmer months although RTRAC estimates higher urban area contribution during the cold months because this RTRAC implementation did not treat O3 titration by NO. Accurate representation of lateral boundary O3 impacts must include appropriate accounting for O3 destruction reactions. OSAT and RTRAC were configured to estimate the contribution to modeled O3 from each of the four lateral faces of the model domain. RTRAC was configured to further stratify the western and northern boundaries by groups of vertical layers. The RTRAC approach showed that the largest O3 contributions to the continental U.S. are from the mid-troposphere, with less contribution from the upper troposphere/lower stratosphere. Inert tracers compared more closely to reactive tracers on average for PM2.5 compared to O3. This close agreement for PM2.5 indicates most of the lateral boundary contribution is from PM2.5 rather than precursor inflow. A strong relationship exists between model predicted PM2.5 boundary contribution and model overestimates of nitrate and organic carbon at IMPROVE monitor locations suggesting global model estimates of these species were overestimated at some places and times.
Keywords: Boundary contribution; Boundary inflow; Source apportionment; OSAT; RTRAC; PSAT;

Evaluation of a method for measuring vehicular PM with a composite filter and a real-time BC instrument by Michael A. Kamboures; Paul L. Rieger; Sherry Zhang; Satya B. Sardar; M.-C. Oliver Chang; Shiou-Mei Huang; Inna Dzhema; Mark Fuentes; Michael T. Benjamin; Annette Hebert; Alberto Ayala (63-71).
As part of the California Air Resources Board's effort to confirm the ability of the vehicular particulate matter (PM) reference method (RM) to measure PM emissions at sub-one milligram per mile (mg/mi), and to explore alternative methods, we evaluated a combination method (CM) that utilizes both gravimetric and real-time particle quantification. PM, collected on a single composite filter is apportioned to the three Federal Test Procedure (FTP) cycle phases using real-time equivalent black carbon (EBC) measurements, reducing the need to carry out separate gravimetric filter measurements for each of the test phases. Four light-duty gasoline vehicles, emitting PM at or below one mg/mi, were dynamometer tested repeatedly on the FTP cycle. PM was quantified by the RM and by two variants of the CM. One variant used photoacoustic spectroscopy to measure EBC (CM-MSS), and the other used an Aethalometer (CM-AE51). The CM was evaluated on repeatability, bias, and correlation with the RM. For the tested vehicles, the observed repeatability of the CM was superior to the RM regardless of the mode of EBC measurement or the test vehicle considered (σCM−MSS = 0.08 mg/mi, σCM−AE51 = 0.07 mg/mi, σRM ≈ 0.11 mg/mi). However, the CM was negatively biased by −0.08 mg/mi, versus the RM, in one of the test vehicles. We attribute the bias in this vehicle's data to organic carbon emissions that were not equivalently collected on the composite filter of the CM. When all data were combined, the correlation between the methods was good (R = 0.90 for CM-MSS vs. RM and R = 0.91 for CM-AE51 vs. RM).
Keywords: Black carbon; Particulate matter; Vehicular; California; Measurement; Regulatory;

Production of hydroxyl radicals from Fe-containing fine particles in Guangzhou, China by Shexia Ma; Ke Ren; Xiaowen Liu; Laiguo Chen; Mei Li; Xiaoying Li; Jian Yang; Bo Huang; Mei Zheng; Zhencheng Xu (72-78).
Reactive oxygen species (ROS) production from ambient fine particles has been correlated with the soluble transition metal content of PM2.5, which also has clear association with particle-mediated cardiopulmonary toxicity. Hydroxyl radical (•OH) is the most harmful ROS species through chemical reactions of redox-active particle components. Atmospheric Fe, as the dominant species of the transition metals in the atmosphere, is associated with •OH generation in ambient particle extracts. Our results revealed that Fe-containing particles (18,730 in total number) contributed approximately 3.7% on average to all detected particles throughout the summer and winter sampling period in Guangzhou, which was clustered into four distinct particle classes, including Fe-rich, Metal-rich, NaK-rich and Dust-rich. Fe-rich class was the dominant one with a fraction of 61%, followed by Dust-rich (14%), Metal-rich (13%). and NaK-rich (12%). The iron oxide was enriched in the Fe-rich class. •OH generation induced by Fe-containing fine particles collected in Guangzhou (GZ) was quantified in a surrogate lung fluid (SLF), and it was found that Fe-containing fine particles were generally much reactive in generating •OH in the presence of four antioxidants (200 μM ascorbate, 300 μM citrate, 100 μM reduced l-glutathione, and 100 μM uric acid). The annual average •OH amount produced in our samples was 132.98 ± 27.43 nmol •OH mg−1 PM2.5. •OH production had a clear seasonal pattern with higher amount in summer and lower in winter. By measuring the amount of total and SLF-soluble metal in our PM2.5 samples using ICP-MS, we found that ROS activities were associated with the ionizable Fe through Fenton type reactions in the Guangzhou PM2.5. Expected burdens of PM2.5 derived •OH in human lung lining fluid suggests that typical daily particulate matter exposure in Guangzhou is already a concern, and it could produce much higher levels of •OH, leading to higher cytotoxicity.
Keywords: Fe-containing particle; Single particle; SPAMS; Reactive oxygen species; Hydroxyl radical; Transition metal;

Development of long-term spatiotemporal models for ambient ozone in six metropolitan regions of the United States: The MESA Air study by Meng Wang; Joshua P. Keller; Sara D. Adar; Sun-Young Kim; Timothy V. Larson; Casey Olives; Paul D. Sampson; Lianne Sheppard; Adam A. Szpiro; Sverre Vedal; Joel D. Kaufman (79-87).
Current epidemiologic studies rely on simple ozone metrics which may not appropriately capture population ozone exposure. For understanding health effects of long-term ozone exposure in population studies, it is advantageous for exposure estimation to incorporate the complex spatiotemporal pattern of ozone concentrations at fine scales.To develop a geo-statistical exposure prediction model that predicts fine scale spatiotemporal variations of ambient ozone in six United States metropolitan regions.We developed a modeling framework that estimates temporal trends from regulatory agency and cohort-specific monitoring data from MESA Air measurement campaigns and incorporates land use regression with universal kriging using predictor variables from a large geographic database. The cohort-specific data were measured at home and community locations. The framework was applied in estimating two-week average ozone concentrations from 1999 to 2013 in models of each of the six MESA Air metropolitan regions.Ozone models perform well in both spatial and temporal dimensions at the agency monitoring sites in terms of prediction accuracy. City-specific leave-one (site)-out cross-validation R2 accounting for temporal and spatial variability ranged from 0.65 to 0.88 in the six regions. For predictions at the home sites, the R2 is between 0.60 and 0.91 for cross-validation that left out 10% of home sites in turn. The predicted ozone concentrations vary substantially over space and time in all the metropolitan regions.Using the available data, our spatiotemporal models are able to accurately predict long-term ozone concentrations at fine spatial scales in multiple regions. The model predictions will allow for investigation of the long-term health effects of ambient ozone concentrations in future epidemiological studies.
Keywords: Ozone; Spatio-temporal; Geo-statistical model; Multi-city; MESA Air;

Detection and attribution of regional CO2 concentration anomalies using surface observations by Fang Zhang; Yukio Fukuyama; Yaqiang Wang; Shuangxi Fang; Ping Li; Tianyi Fan; Lingxi Zhou; Xingang Liu; Frank Meinhardt; Patrizio Emiliani (88-101).
In this study, observed episodes of CO2 concentrations at eight Northern Hemisphere (NH) sites from 1993 to 2012 were analyzed. Five-day back trajectories were calculated for a potential source contribution function (PSCF) analysis. A normalized weight factor related to the occurrence of the episodes was applied to derive more reasonable CO2 elevations and sequestrations. Weighted elevated (▵CO2(W_E)) and sequestered (▵CO2(W_S)) CO2 episodes had large spatial discrepancies due to the differentiation of strength and patterns of CO2 emissions/sinks in different regions. The most significant enhancement in CO2 episodes was observed at Asian sites: ▵CO2(W_E) increased by approximately 56% at an annual rate of ∼4% yr−1 from 1995 to 2010 at Waliguan (WLG) and by approximately 39% (∼3% yr−1) from 1997 to 2012 at Yonagunijima (YON). According to the PSCF analysis, these increases are largely attributed to the rapid increase in emissions in China. However, ▵CO2(W_S) was also enhanced by 34.4% with a growth rate of 2.3% yr−1 at WLG from 1995 to 2010 and ∼26.2% (1.7% yr−1) at YON from 1997 to 2012. Both ▵CO2(W_E) and ▵CO2(W_S) showed decreasing or relatively flat trends at Monte Cimone and Schauinsland, indicating reductions in emissions and sinks in central Europe. The different intensities/trends in emissions and sinks observed at different sites in the NH show that estimating future CO2 levels is a complex problem. Atmospheric inverse and process-based ecosystem models should use more regional input data at high temporal and spatial resolutions for future carbon flux estimations.
Keywords: Carbon dioxide (CO2); Elevated and sequestered episodes; Potential source contribution function (PSCF); Emissions and sinks; Long-term trends;

Health effects of ambient levels of respirable particulate matter (PM) on healthy, young-adult population by William J. Shaughnessy; Mohan M. Venigalla; David Trump (102-111).
There is an absence of studies that define the relationship between ambient particulate matter (PM) levels and adverse health outcomes among the young and healthy adult sub-group. In this research, the relationship between exposures to ambient levels of PM in the 10 micron (PM10) and 2.5 micron (PM2.5) size fractions and health outcomes in members of the healthy, young-adult subgroup who are 18–39 years of age was examined. Active duty military personnel populations at three strategically selected military bases in the United States were used as a surrogate to the control group. Health outcome data, which consists of the number of diagnoses for each of nine International Classification of Diseases, 9th Revision (ICD-9) categories related to respiratory illness, were derived from outpatient visits at each of the three military bases. Data on ambient concentrations of particulate matter, specifically PM10 and PM2.5, were obtained for these sites. The health outcome data were correlated and regressed with the PM10 and PM2.5 data, and other air quality and weather-related data on a daily and weekly basis for the period 1998 to 2004. Results indicate that at Fort Bliss, which is a US Environmental Protection Agency designated non-attainment area for PM10, a statistically significant association exists between the weekly-averaged number of adverse health effects in the young and healthy adult population and the corresponding weekly-average ambient PM10 concentration. A least squares regression analysis was performed on the Fort Bliss data sets indicated that the health outcome data is related to several environmental parameters in addition to PM10. Overall, the analysis estimates a .6% increase in the weekly rate of emergency room visits for upper respiratory infections for every 10 μg/m3 increase in the weekly-averaged PM10 concentration above the mean. The findings support the development of policy and guidance opportunities that can be developed to mitigate exposures to particulate matter.
Keywords: Particulate matter; PM10; PM2.5; Health effects; Young healthy adults; Upper respiratory diseases;

Particulate and gas-phase products from the atmospheric degradation of chlorpyrifos and chlorpyrifos-oxon by Esther Borrás; Milagros Ródenas; Mónica Vázquez; Teresa Vera; Amalia Muñoz (112-120).
The phosphorothioate structure is highly present in several pesticides. However, there is a lack of information about its degradation process in air and the secondary pollutants formed. Herein, the atmospheric reactions of chlorpyrifos, one of the most world-used insecticide, and its main degradation product – chlorpyrifos-oxon – are described. The photo-oxidation under the presence of NOx was studied in a large outdoor simulation chamber for both chlorpyrifos and chlorpyrifos-oxon, observing a rapid degradation (Half lifetime < 3.5 h for both compounds). Also, the photolysis reactions of both were studied. The formation of particulate matter (aerosol mass yield ranged 6–59%) and gaseous products were monitored. The chemical composition of minor products was studied, identifying 15 multi-oxygenated derivatives. The most abundant products were ring-retaining molecules such as 3,5,6-trichloropyridin-2-ol and ethyl 3,5,6-trichloropyridin-2-yl hydrogen phosphate. An atmospheric degradation mechanism has been amplified based on an oxidation started with OH-nucleophilic attack to P=S bond.Display Omitted
Keywords: Chlorpyrifos; Chlorpyrifos-oxon; Insecticide; SOA; Photo-oxidation; Multi-oxygenated products;

Effects of moisture content on wind erosion thresholds of biochar by F.C. Silva; C. Borrego; J.J. Keizer; J.H. Amorim; F.G.A. Verheijen (121-128).
Biochar, i.e. pyrolysed biomass, as a soil conditioner is gaining increasing attention in research and industry, with guidelines and certifications being developed for biochar production, storage and handling, as well as for application to soils. Adding water to biochar aims to reduce its susceptibility to become air-borne during and after the application to soils, thereby preventing, amongst others, human health issues from inhalation. The Bagnold model has previously been modified to explain the threshold friction velocity of coal particles at different moisture contents, by adding an adhesive effect. However, it is unknown if this model also works for biochar particles. We measured the threshold friction velocities of a range of biochar particles (woody feedstock) under a range of moisture contents by using a wind tunnel, and tested the performance of the modified Bagnold model. Results showed that the threshold friction velocity can be significantly increased by keeping the gravimetric moisture content at or above 15% to promote adhesive effects between the small particles. For the specific biochar of this study, the modified Bagnold model accurately estimated threshold friction velocities of biochar particles up to moisture contents of 10%.Display Omitted
Keywords: Biochar; Threshold friction velocity; Wind tunnel; Particle size; Bagnold model;

On-road PM2.5 pollution exposure in multiple transport microenvironments in Delhi by Rahul Goel; Shahzad Gani; Sarath K. Guttikunda; Daniel Wilson; Geetam Tiwari (129-138).
PM2.5 pollution in Delhi averaged 150 μg/m3 from 2012 through 2014, which is 15 times higher than the World Health Organization's annual-average guideline. For this setting, we present on-road exposure of PM2.5 concentrations for 11 transport microenvironments along a fixed 8.3-km arterial route, during morning rush hour. The data collection was carried out using a portable TSI DustTrak DRX 8433 aerosol monitor, between January and May (2014). The monthly-average measured ambient concentrations varied from 130 μg/m3 to 250 μg/m3. The on-road PM2.5 concentrations exceeded the ambient measurements by an average of 40% for walking, 10% for cycle, 30% for motorised two wheeler (2W), 30% for open-windowed (OW) car, 30% for auto rickshaw, 20% for air-conditioned as well as for OW bus, 20% for bus stop, and 30% for underground metro station. On the other hand, concentrations were lower by 50% inside air-conditioned (AC) car and 20% inside the metro rail carriage. We find that the percent exceedance for open modes (cycle, auto rickshaw, 2W, OW car, and OW bus) reduces non-linearly with increasing ambient concentration. The reduction is steeper at concentrations lower than 150 μg/m3 than at higher concentrations. After accounting for air inhalation rate and speed of travel, PM2.5 mass uptake per kilometer during cycling is 9 times of AC car, the mode with the lowest exposure. At current level of concentrations, an hour of cycling in Delhi during morning rush-hour period results in PM2.5 dose which is 40% higher than an entire-day dose in cities like Tokyo, London, and New York, where ambient concentrations range from 10 to 20 μg/m3.
Keywords: PM2.5; Air pollution; Road transport; Traffic; Exposure; Delhi; India;

Accurate representation of air pollutant dispersion is essential for environmental management and planning purposes. In this study, semi-empirical relationships of turbulence intensity (σu/u*, σv/u* and σw/u*) as a function of surface layer scaling and local stability are developed following boundary layer similarity concepts at Ranchi, a complex terrain in Jharkhand, Eastern India for various seasons. The impact of the new turbulence parameterization for air pollution dispersion simulation is studied by incorporating the same in the Hanna scheme of FLEXPART-WRF Lagrangian Particle dispersion model over study region. The model is used to estimate the ground level concentrations of nitrogen oxides (NOx) due to industrial and vehicular sources in study region. The meteorological parameters needed in air-quality simulation are simulated using the Advanced Research WRF (ARW) mesoscale model at high resolution (3 km). Three turbulence schemes (YSU, MYNN2 and ACM2) in ARW are alternatively tested in dispersion simulation and comparisons are made with available air quality data for eight days in different seasons (winter, pre-monsoon, monsoon and post-monsoon). Simulations with FLEXPART revealed distinct seasonal variation of dispersion patterns. It has been found that the new turbulence intensity relationships in FLEXPART improved the NOx concentration estimates by reducing the negative bias seen with default Hanna scheme. Further, the ARW simulated meteorological parameters using ACM2 and MYNN2 significantly reduced the bias in modeled pollutant concentrations. The study demonstrates the utility of high quality seasonal turbulence measurements in pollution dispersion model for better diffusion parameterization needed in air quality modeling.
Keywords: FLEXPART-WRF; Complex terrain; Air quality; Turbulence intensity;

The Uintah Basin in Utah, U.S.A. experiences high concentrations of ozone during some winters due to strong, multi-day temperature inversions that facilitate the buildup of pollution from local sources, including the oil and gas industry. Together, elevation of monitoring sites and proximity to oil and gas wells explain as much as 90% of spatial variability in surface ozone concentrations during inversion episodes (i.e., R2 = 0.90). Inversion conditions start earlier and last longer at lower elevations, at least in part because lower elevations are more insulated from winds aloft that degrade inversion conditions and dilute produced ozone. Surface air transport under inversions is dominated by light, diurnal upslope–downslope flow that limits net transport distances. Thus, different areas of the Basin are relatively isolated from each other, allowing spatial factors like elevation and proximity to sources to strongly influence ozone concentrations at individual sites.
Keywords: Winter ozone; Organic compounds; Spatial distribution; Oil and gas industry;

Images and properties of individual nucleated particles by Zoltán Németh; Mihály Pósfai; Ilona Nyirő-Kósa; Pasi Aalto; Markku Kulmala; Imre Salma (166-170).
Atmospheric aerosol particles were collected in Budapest, Hungary in April–June onto lacey Formvar substrates by using an electrostatic precipitator during the beginning phase of the particle growth process in ten nucleation and growth events. Median contribution of the nucleated particles - expressed as the concentration of particles with a diameter between 6 and 25 nm to the total particle number concentration – was 55%, and the median electrical mobility diameter of the particles was approximately 20 nm. The sample was investigated using high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy. Major types of individual particles such as soot, sulphate/organic and tar ball particles were identified in the sample. In addition, particles with an optical diameter range of 10–30 nm were also observed. They clearly differed from the other particle types, showed homogeneous contrast in the bright-field TEM images, and evaporated within tens of seconds when exposed to the electron beam. They were interpreted as representatives of freshly nucleated particles.
Keywords: Atmospheric nucleation; Electron microscopy;

Nitrogen deposition and its effect on carbon storage in Chinese forests during 1981–2010 by Fengxue Gu; Yuandong Zhang; Mei Huang; Bo Tao; Huimin Yan; Rui Guo; Jie Li (171-179).
Human activities have resulted in dramatically increased nitrogen (N) deposition worldwide, which is closely linked to the carbon (C)-cycle processes and is considered to facilitate terrestrial C sinks. In this study, we firstly estimated the spatial and temporal variations of N deposition during 1981–2010 based on a new algorithm; then we used a newly improved process-based ecosystem model, CEVSA2, to examine the effects of N deposition on C storage in Chinese forests. The results show that the rate of N deposition increased by 0.058 g N m−2 yr−1 between 1981 and 2010. The N deposition rate in 2010 was 2.32 g N m−2 yr−1, representing a large spatial variation from 0 to 0.25 g N m−2 yr−1 on the northwestern Qinghai–Tibet Plateau to over 4.5 g N m−2 yr−1 in the southeastern China. The model simulations suggest that N deposition induced a 4.78% increase in the total C storage in Chinese forests, most of which accumulated in vegetation. C storage increased together with the increase in N deposition, in both space and time. However, N use efficiency was highest when N deposition was 0.4–1.0 g N m−2 yr−1. We suggest conducting more manipulation experiments and observations in different vegetation types, which will be greatly helpful to incorporate additional processes and mechanisms into the ecosystem modeling. Further development of ecosystem models and identification of C–N interactions will be important for determining the effects of N input on C cycles on both regional and global scales.
Keywords: Nitrogen deposition; Carbon storage; Nitrogen use efficiency; C–N interactions; Chinese forests; CEVSA2 model;

Through-tunnel estimates of vehicle fleet emission factors by Peter Brimblecombe; Thomas Townsend; Chui Fong Lau; Agata Rakowska; Tat Leung Chan; Griša Močnik; Zhi Ning (180-189).
On-road measurements of traffic-related gas and particle pollutant concentrations in three tunnels in Hong Kong and high resolution pollutant concentration profiles obtained while driving through the tunnels were used to derive the individual pollutant gradients using parametric and non-parametric (Sen–Thiel) slopes and compared with the commonly used entrance-exit two points calculation. The fuel based emission factors of measured pollutants for individual tunnels at different times of day were derived from gradients using a new method based on fuel carbon balance principle. Combined with the tunnel traffic volume and composition, the average tunnel emission factors were analyzed by linear regression to derive the diesel fleet emission factors. Average nitrogen oxides (NOx) and black carbon (BC) emission factor for diesel fleets are 29.3 ± 11.0 gNO2 kg−1 and 1.28 ± 0.76 g kg−1 of fuel, respectively. The results from the study were compared with the emission data from vehicle chasing approaches and the literature, showing reasonable agreement. Practical limitations and future direction for improvement of our method were also discussed. The method presented in this study provides a convenient drive-through approach for fast determination of tunnel and individual vehicle fleet emission factors. It can be used as an effective and fast approach to validate the emission inventory and to evaluate the effectiveness of policy intervention on the traffic emissions.
Keywords: Hong Kong; Black carbon; Ultrafine particles; Carbon monoxide; Tunnel; Emission factor;

Source apportionment of PM10 mass and particulate carbon in the Kathmandu Valley, Nepal by Bong Mann Kim; Jin-Soo Park; Sang-Woo Kim; Hyunjae Kim; Haeun Jeon; Chaeyoon Cho; Ji-Hyoung Kim; Seungkyu Hong; Maheswar Rupakheti; Arnico K. Panday; Rokjin J. Park; Jihyung Hong; Soon-Chang Yoon (190-199).
The Kathmandu Valley in Nepal is a bowl-shaped urban basin in the Himalayan foothills with a serious problem of fine particulate air pollution that impacts local health and impairs visibility. Particulate carbon concentrations have reached severe levels that threaten the health of 3.5 million local residents. Moreover, snow and ice on the Himalayan mountains are melting as a result of additional warming due to particulate carbon, especially high black carbon concentrations. To date, the sources of the Valley's particulate carbon and the impacts of different sources on particulate carbon concentrations are not well understood. Thus, before an effective control strategy can be developed, these particulate carbon sources must be identified and quantified. Our study has found that the four primary sources of particulate carbon in the Kathmandu Valley during winter are brick kilns, motor vehicles, fugitive soil dust, and biomass/garbage burning. Their source contributions are quantified using a recently developed new multivariate receptor model SMP. In contrast to other highly polluted areas such as China, secondary contribution is almost negligible in Kathmandu Valley. Brick kilns (40%), motor vehicles (37%) and biomass/garbage burning (22%) have been identified as the major sources of elemental carbon (black carbon) in the Kathmandu Valley during winter, while motor vehicles (47%), biomass/garbage burning (32%), and soil dust (13%) have been identified as the most important sources of organic carbon. Our research indicates that controlling emissions from motor vehicles, brick kilns, biomass/garbage burning, and soil dust is essential for the mitigation of the particulate carbon that threatens public health, impairs visibility, and influences climate warming within and downwind from the Kathmandu Valley. In addition, this paper suggests several useful particulate carbon mitigation methods that can be applied to Kathmandu Valley and other areas in South Asia with similar sources and high particulate carbon concentrations.
Keywords: PM10; Particulate carbon; Source apportionment; SMP model; Kathmandu;

Future atmospheric abundances and climate forcings from scenarios of global and regional hydrofluorocarbon (HFC) emissions by Guus J.M. Velders; David W. Fahey; John S. Daniel; Stephen O. Andersen; Mack McFarland (200-209).
Hydrofluorocarbons (HFCs) are manufactured for use as substitutes for ozone-depleting substances that are being phased out globally under Montreal Protocol regulations. While HFCs do not deplete ozone, many are potent greenhouse gases that contribute to climate change. Here, new global scenarios show that baseline emissions of HFCs could reach 4.0–5.3 GtCO2-eq yr−1 in 2050. The new baseline (or business-as-usual) scenarios are formulated for 10 HFC compounds, 11 geographic regions, and 13 use categories. The scenarios rely on detailed data reported by countries to the United Nations; projections of gross domestic product and population; and recent observations of HFC atmospheric abundances. In the baseline scenarios, by 2050 China (31%), India and the rest of Asia (23%), the Middle East and northern Africa (11%), and the USA (10%) are the principal source regions for global HFC emissions; and refrigeration (40–58%) and stationary air conditioning (21–40%) are the major use sectors. The corresponding radiative forcing could reach 0.22–0.25 W m−2 in 2050, which would be 12–24% of the increase from business-as-usual CO2 emissions from 2015 to 2050. National regulations to limit HFC use have already been adopted in the European Union, Japan and USA, and proposals have been submitted to amend the Montreal Protocol to substantially reduce growth in HFC use. Calculated baseline emissions are reduced by 90% in 2050 by implementing the North America Montreal Protocol amendment proposal. Global adoption of technologies required to meet national regulations would be sufficient to reduce 2050 baseline HFC consumption by more than 50% of that achieved with the North America proposal for most developed and developing countries.
Keywords: HFC; Radiative forcing; Climate; Montreal Protocol; CO2-eq emissions;

Source and transportation of summer dust over the Tibetan Plateau by Rui Jia; Yuzhi Liu; Bin Chen; Zhijuan Zhang; Jianping Huang (210-219).
Satellite observational evidences (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, CALIPSO) have presented that the Tibetan Plateau (TP) is subject to heavy loading of dust aerosols during summer. Combining back trajectory and weather system analyses, the source and transportation of summer Tibetan dust from 2007 to 2014 were investigated. The Tibetan dust is mainly from the Taklimakan Desert and partially from the Gurbantunggut Desert and Great Indian Thar Desert. Case study indicates that the meteorological conditions together with the topography benefit the dust emission adjacent to the TP and the transport toward the plateau. When a cold advection or front developed by strong cold advection passes, dust particles are emitted into the atmosphere from the Taklimakan and Gurbantunggut deserts and then transported to the northern slope of the TP with northeasterly wind induced by the Altai and Tian Shan mountains. For the period from 2007 to 2014, the correlation coefficient of the monthly frequencies of summer dust events over the TP and cold advection passing the Taklimakan and Gurbantunggut deserts were as high as 0.68 and 0.34, respectively. Differently, although the correlation is limited, much TP dust mobilized from the Great Indian Thar Desert is associated with the passing low-pressure system activity and generally polluted by anthropogenic aerosols. The polluted dust is further transported to the southern slope of the TP by the prevailing westerly wind. Investigations on the source and transportation of summer dust over the TP provide a solid foundation of data that can be used to reveal the role of TP dust in the radiation balance, hydrological cycle, and monsoon cycle in India and East Asia.
Keywords: Tibetan plateau; Summer dust; Source; Transportation;

Field comparison of portable and stationary instruments for outdoor urban air exposure assessments by M. Viana; I. Rivas; C. Reche; A.S. Fonseca; N. Pérez; X. Querol; A. Alastuey; M. Álvarez-Pedrerol; J. Sunyer (220-228).
The performance of three portable monitors (micro-aethalometer AE51, DiscMini, Dusttrak DRX) was assessed for outdoor air exposure assessment in a representative Southern European urban environment. The parameters evaluated were black carbon, particle number concentration, alveolar lung-deposited surface area, mean particle diameter, PM10, PM2.5 and PM1. The performance was tested by comparison with widely used stationary instruments (MAAP, CPC, SMPS, NSAM, GRIMM aerosol spectrometer). Results evidenced a good agreement between most portable and stationary instruments, with R2 values mostly >0.80. Relative differences between portable and stationary instruments were mostly <20%, and <10% between different units of the same instrument. The only exception was found for the Dusttrak DRX measurements, for which occasional concentration jumps in the time series were detected. Our results validate the performance of the black carbon, particle number concentration, particle surface area and mean particle diameter monitors as indicative instruments (tier 2) for outdoor air exposure assessment studies.Display OmittedPortable monitors evaluated for BC, and particle number, mean size, and surface area are suitable instruments for population exposure assessments in urban outdoor air.
Keywords: Intercomparison; Relative error; Uncertainty; Performance; Outdoor; Indoor;

Source contributions of urban PM2.5 in the Beijing–Tianjin–Hebei region: Changes between 2006 and 2013 and relative impacts of emissions and meteorology by Xin Li; Qiang Zhang; Yang Zhang; Bo Zheng; Kai Wang; Ying Chen; Timothy J. Wallington; Weijian Han; Wei Shen; Xiaoye Zhang; Kebin He (229-239).
Anthropogenic emissions in China have been controlled for years to improve ambient air quality. However, severe haze events caused by atmospheric aerosols with aerodynamic diameter less than or equal to 2.5 μm (PM2.5) have continued to occur, especially in the Beijing–Tianjin–Hebei (BTH) region. The Chinese government has set an ambitious goal to reduce urban PM2.5 concentrations by 25% in BTH by 2017 relative to the 2012 levels. Source apportionment (SA) is necessary to the development of the effective emission control strategies. In this work, the Comprehensive Air Quality Model with extensions (CAMx) with the Particulate Source Apportionment Technology (PSAT) is applied to the China domain for the years 2006 and 2013. Ambient surface concentrations of PM2.5 and its components are generally well reproduced. To quantify the contributions of each emission category or region to PM2.5 in BTH, the total emissions are divided into 7 emission categories and 11 source regions. The source contributions determined in this work are generally consistent with results from previous work. In 2013, the industrial (44%) and residential (27%) sectors are the dominant contributors to urban PM2.5 in BTH. The residential sector is the largest contributor in winter; the industry sector dominates in other seasons. A slight increasing trend (+3% for industry and +6% for residential) is found in 2013 relative to 2006, necessitating more attention to these two sectors. Local emissions make the largest contribution (40%–60%) for all receptors. Change of source contribution of PM2.5 in Beijing and northern Hebei are dominate by change of local emission. However, for Tianjin, and central and southern Hebei, change of meteorology condition are as important as change of emission, because regional inflow in these areas is more important than in Beijing and northern Hebei and can increase under unfavorable weather conditions, indicating a strong need for regional joint emission control efforts. The results in this study enhance the quantitative understanding of the source–receptor relationships and provide an important basis for policymaking to advance the control of PM2.5 pollution in China.
Keywords: Source apportionment; Regional inflow; Meteorological influence; Joint emission control;

A new methodology to assess the performance and uncertainty of source apportionment models II: The results of two European intercomparison exercises by C.A. Belis; F. Karagulian; F. Amato; M. Almeida; P. Artaxo; D.C.S. Beddows; V. Bernardoni; M.C. Bove; S. Carbone; D. Cesari; D. Contini; E. Cuccia; E. Diapouli; K. Eleftheriadis; O. Favez; I. El Haddad; R.M. Harrison; S. Hellebust; J. Hovorka; E. Jang; H. Jorquera; T. Kammermeier; M. Karl; F. Lucarelli; D. Mooibroek; S. Nava; J.K. Nøjgaard; P. Paatero; M. Pandolfi; M.G. Perrone; J.E. Petit; A. Pietrodangelo; P. Pokorná; P. Prati; A.S.H. Prevot; U. Quass; X. Querol; D. Saraga; J. Sciare; A. Sfetsos; G. Valli; R. Vecchi; M. Vestenius; E. Yubero; P.K. Hopke (240-250).
The performance and the uncertainty of receptor models (RMs) were assessed in intercomparison exercises employing real-world and synthetic input datasets. To that end, the results obtained by different practitioners using ten different RMs were compared with a reference. In order to explain the differences in the performances and uncertainties of the different approaches, the apportioned mass, the number of sources, the chemical profiles, the contribution-to-species and the time trends of the sources were all evaluated using the methodology described in Belis et al. (2015).In this study, 87% of the 344 source contribution estimates (SCEs) reported by participants in 47 different source apportionment model results met the 50% standard uncertainty quality objective established for the performance test. In addition, 68% of the SCE uncertainties reported in the results were coherent with the analytical uncertainties in the input data.The most used models, EPA-PMF v.3, PMF2 and EPA-CMB 8.2, presented quite satisfactory performances in the estimation of SCEs while unconstrained models, that do not account for the uncertainty in the input data (e.g. APCS and FA-MLRA), showed below average performance. Sources with well-defined chemical profiles and seasonal time trends, that make appreciable contributions (>10%), were those better quantified by the models while those with contributions to the PM mass close to 1% represented a challenge.The results of the assessment indicate that RMs are capable of estimating the contribution of the major pollution source categories over a given time window with a level of accuracy that is in line with the needs of air quality management.
Keywords: Source apportionment; Receptor models; Intercomparison exercise; Model performance indicators; Model uncertainty; Particulate matter;

Development of an in situ derivatization technique for rapid analysis of levoglucosan and polar compounds in atmospheric organic aerosol by Rebecca J. Sheesley; Mark Mieritz; Jeff T. DeMinter; Brandon R. Shelton; James J. Schauer (251-255).
A novel thermal desorption gas chromatography mass spectrometry (TD-GCMS) technique was developed for the analysis of levoglucosan and other polar compounds in atmospheric organic aerosol. The method employs an in situ derivatization to add tri-methylsilyl groups to alcohol functional groups on simple carbohydrates, like levoglucosan and sterols. The new method was then demonstrated on a set of 40 filter samples collected in Fresno, CA. The results from the in situ silylation TD-GCMS method were compared, using levoglucosan, with a solvent extraction, high-volume injection GCMS method resulting in an r2 = 0.91.
Keywords: Levoglucosan; Thermal desorption GCMS; Biomass burning; Atmospheric particulate matter;

Global modeling of the C1–C3 alkyl nitrates using STOCHEM-CRI by M.A.H. Khan; M.C. Cooke; S.R. Utembe; W.C. Morris; A.T. Archibald; R.G. Derwent; M.E. Jenkin; A.J. Orr-Ewing; C.M. Higgins; C.J. Percival; K.E. Leather; D.E. Shallcross (256-267).
The atmospheric global budget and distribution of C1–C3 alkyl nitrates have been investigated using a global three-dimensional chemistry transport model, STOCHEM-CRI. Alkyl nitrates (RONO2) are significant NOx reservoir species and the more detailed VOC oxidation mechanism (CRI v2-R5) leads to greater photochemical production. RONO2 are significant sources of NOx in regions remote from NOx sources. The study shows that the global burden and the atmospheric life-time of C1–C3 alkyl nitrates are 113 Gg and 9–10 days, respectively, which are in excellent agreement with estimates established by previous studies. The abundance of alkyl nitrates have been found to be higher in the continental atmosphere, with CH3ONO2 mixing ratios up to 20 ppt over the Amazon rainforest. Up to 15, 10, 2, and 5 ppt of modelled CH3ONO2, C2H5ONO2, n-C3H7ONO2 and i-C3H7ONO2 have been found in the northern hemisphere over regions with large anthropogenic emissions of NOx and VOCs. The combination of atmospheric production and long-range transport led to high alkyl nitrate levels at high latitudes. The model performance for C1–C3 alkyl nitrates was established using observations from nine flights and nine field campaigns. The comparison shows a tendency towards model under-prediction of the observations, particularly in the southern hemispheric marine boundary layer, possibly due to the absence of oceanic production mechanisms and air-sea exchange processes in the model. The discrepancies between model and observed seasonal cycles, especially of CH3ONO2, in both hemispheres are discussed.
Keywords: Global burden; Atmospheric life-times; Photochemical production; Long-range transport;

Dynamics of ozone and nitrogen oxides at Summit, Greenland: I. Multi-year observations in the snowpack by Brie Van Dam; Detlev Helmig; Claudia Toro; Paul Doskey; Louisa Kramer; Keenan Murray; Laurens Ganzeveld; Brian Seok (268-284).
A multi-year investigation of ozone (O3) and nitrogen oxides (NOx) in snowpack interstitial air down to a depth of 2.8 m was conducted at Summit, Greenland, to elucidate mechanisms controlling the production and destruction of these important trace gases within the snow. Snowpack O3 values ranged from 30 to 40 ppbv during winter months, and dropped below 10 ppbv in summer. Wintertime NOx levels were low at all depths in the snowpack (below 10 pptv for NO and below 25 pptv for NO2). In the summer, NO values up to 120 pptv, and NO2 mixing ratios up to ∼700 pptv were observed. O3 loss within the snowpack was observed throughout all seasons. The magnitude of the O3 loss rate tracked the seasonal and diurnal cycle of incoming short wave solar radiation. Production of NO within a shallow layer of the snowpack was recorded during the spring and summer months. NO2 production also occurred, and heightened levels were measured down to 2.5 m in the snowpack. The average daily maximum in NO was observed at solar noon, and the minimum was seen during night. The daily peak in NO2 was on average 7 h shifted from the incoming solar radiation and NO maxima. NOx levels in interstitial air during spring were enhanced relative to summer and fall. The influence of meteorological effects such as wind pumping on snowpack interstitial air levels of O3 and NOx was investigated using case study periods. Increased snowpack ventilation during high wind events was found to yield enhancement in snowpack NOx, with this effect being enhanced during times when O3 was elevated in ambient air. This behavior suggests that O3 is involved in NOx production in the snowpack. This extensive set of observations is used to re-evaluate physical and chemical processes that describe the dynamic O3 and NOx chemistry occurring within snowpack interstitial air at Summit.
Keywords: Cryosphere; Photochemistry; Atmosphere; Gas exchange; Ozone; Nitrogen oxides;