Atmospheric Environment (v.110, #C)

Characteristics of carbonaceous aerosols emitted from peatland fire in Riau, Sumatra, Indonesia (2): Identification of organic compounds by Yusuke Fujii; Haruo Kawamoto; Susumu Tohno; Masafumi Oda; Windy Iriana; Puji Lestari (1-7).
Smoke emitted from Indonesian peatland fires has caused dense haze and serious air pollution in Southeast Asia such as visibility impairment and adverse health impacts. To mitigate the Indonesian peatland fire aerosol impacts, an effective strategy and international framework based on the latest scientific knowledge needs to be established. Although several attempts have been made, limited data exist regarding the chemical characteristics of peatland fire smoke for the source apportionment. In order to identify the key organic compounds of peatland fire aerosols, we conducted intensive field studies based on ground-based and source-dominated sampling of PM2.5 in Riau Province, Sumatra, Indonesia, during the peatland fire seasons in 2012. Levoglucosan was the most abundant compound among the quantified organic compounds at 8.98 ± 2.28% of the PM2.5 mass, followed by palmitic acid at 0.782 ± 0.163% and mannosan at 0.607 ± 0.0861%. Potassium ion was not appropriate for an indicator of Indonesian peatland fires due to extremely low concentrations associated with smoldering fire at low temperatures. The vanillic/syringic acids ratio was 1.06 ± 0.155 in this study and this may be a useful signature profile for peatland fire emissions. Particulate n-alkanes also have potential for markers to identify impact of Indonesian peatland fire source at a receptor site.
Keywords: Peatland fire; PM2.5; Lignin; n-alkane; Indonesia;

Multi-metric measurement of personal exposure to ultrafine particles in selected urban microenvironments by Andrea Spinazzè; Andrea Cattaneo; Damiano R. Scocca; Matteo Bonzini; Domenico M. Cavallo (8-17).
At the beginning of the study, our hypothesis was that visiting certain microenvironments (MEs) is one of the most important determinants of personal exposure to ultrafine particles (UFP) and that moving between microenvironments significantly differentiates exposure. The overall aim of this study is to perform relevant exposure measurements to extend our knowledge on environmental exposure to UFP in urban environments. The UFP concentrations in different urban MEs were measured by personal monitoring in repeated sampling campaigns along a fixed route. The measurement runs were performed on one-week periods and at different times of day (AM: 08.00–10.30; PM: 16.00–18.30) and repeated in different periods of the year (winter, spring, summer, and autumn) for a total of 56 runs (>110 h). Measurements included on-line monitoring of the UFP particle number concentration (PNC), mean diameter (mean-d) and lung-deposited surface-area (LDSA). Additionally, the PNC, particle mass concentration (PMC) profiles for quasi-ultrafine particles (QUFP; PM0.25) were estimated. A significant seasonal difference in the PNC and PMC, mean diameter and surface area was observed as well as between different times of the day and days of the week. In addition, differences in the UFP concentrations were also found in each ME, and there were specific mean-diameter and surface area concentrations. In general, the mean particle diameters showed an inverse relationship with the PNC, while the LDSA had the opposite behaviour. Appreciable differences among all MEs and monitoring periods were observed; the concentration patterns and variations seemed related to the typical sources of urban pollutants (traffic), proximity to sources and time of day. The highest exposures were observed for walking or biking along high-trafficked routes and while using public buses. The UFP exposure levels in modern cars, equipped with high-efficiency filters and in air recirculation mode, were significantly lower.
Keywords: Air pollution; Ultrafine particles; Personal exposure; Particle size; Surface area; Commuting;

Varietal screening of ozone sensitivity in Mediterranean durum wheat (Triticum durum, Desf.) by Robert Monga; Riccardo Marzuoli; Rocìo Alonso; Victoria Bermejo; Ignacio González-Fernández; Franco Faoro; Giacomo Gerosa (18-26).
This study investigated the ozone (O3) sensitivity of five cultivars of durum wheat (Triticum durum) grown in Open-Top Chambers (OTC) during the 2013 growing season. Two levels of ozone were applied during daylight hours: +50% and −50% of ambient ozone concentration respectively in O3-enriched OTC and charcoal-filtered OTC. Results suggest that the significant differences observed in agronomic parameters, were more cultivar-dependent rather than ozone-dependent. Two cultivars showed a significant reduction of aboveground biomass due to ozone (−19.7% and −25%), however only one of them showed also a significant reduction in grain yield (−16%). Stomatal conductance was significantly reduced by ozone fumigation up to −33% in the afternoon measuring cycle. No significant effects on chlorophyll fluorescence were found, nor correlation was observed between ozone-like symptoms severity (leaf chlorotic/necrotic spots) and yield reduction, suggesting that these parameters cannot be indicative of ozone sensitivity/tolerance. These results may be useful for the selection of durum wheat genotypes more adapted for the cultivation in geographical areas where tropospheric ozone is particularly high, but also for the future definition of consistent dose–response relationships to be used in the ozone risk assessment evaluation for the Mediterranean countries.
Keywords: Durum wheat; Ozone; Grain yield; Stomatal conductance;

Henry's Law constants (H) and octanol–air partition coefficients (KOA) for polycyclic aromatic hydrocarbons (PAHs) and selected nitrogen-, oxygen- and sulfur-containing derivatives have been computed using the COSMO-RS method between −5 and 40 °C in 5 °C intervals. The accuracy of the estimation was assessed by comparison of COSMOtherm values with published experimental temperature-dependence data for these and similar PAHs. COSMOtherm log H estimates with temperature-variation for parent PAHs are shown to have a root-mean-square (RMS) error of 0.38 (PAH), based on available validation data. Estimates of O-, N- and S-substituted derivative log H values are found to have RMS errors of 0.30 at 25 °C. Log KOA estimates with temperature variation from COSMOtherm are shown to be strongly correlated with experimental values for a small set of unsubstituted PAHs, but with a systematic underestimation and associated RMS error of 1.11. Similar RMS error of 1.64 was found for COSMO-RS estimates of a group of critically-evaluated log KOA values at room temperature. Validation demonstrates that COSMOtherm estimates of H and KOA are of sufficient accuracy to be used for property screening and preliminary environmental risk assessment, and perform very well for modeling the influence of temperature on partitioning behavior in the temperature range −5 to 40 °C. Temperature-dependent shifts of up to 2 log units in log H and one log unit for log KOA are predicted for PAH species over the range −5 and 40 °C. Within the family of PAH molecules, COSMO-RS is sufficiently accurate to make it useful as a source of estimates for modeling purposes, following corrections for systematic underestimation of KOA. Average changes in the values for log H and log KOA upon substitution are given for various PAH substituent categories, with the most significant shifts being associated with the ionizing nitro functionality and keto groups.Display Omitted
Keywords: Henry's law constants; Temperature dependence; COSMOtherm; Polycyclic aromatic compounds; Air–water partitioning; Octanol–air partitioning;

Aerosol chemical composition and light scattering during a winter season in Beijing by Jun Tao; Leiming Zhang; Jian Gao; Han Wang; Faihe Chai; Shulan Wang (36-44).
To evaluate PM2.5 contributions to light scattering under different air pollution levels, PM2.5 and its major chemical components, PM10, size-segregated water-soluble ions, and aerosol scattering coefficient (bsp) under dry conditions were measured at an urban site in Beijing in January 2013 when heavy pollution events frequently occurred. Measurements were categorized into three pollution levels including heavy-polluted (Air Quality Index (AQI) ≥ 200), light-polluted (200 > AQI ≥ 100) and clean periods (AQI < 100). The average PM2.5 mass concentration was 248 μg m−3 during the heavy-polluted period, which was 2.4 and 5.6 times of those during the light-polluted (104 μg m−3) and clean (44 μg m−3) periods, respectively. The concentrations of SO4 2−, NO3 and NH4 + increased much more than those of OC and EC during the heavy-polluted period compared with those during the light-polluted and clean periods. Good correlations between PM2.5 and bsp were found (R2 > 0.95) during the different pollution levels. The mass scattering efficiency (MSE) of PM2.5 was 4.9 m2 g−1 during the heavy-polluted period, which was higher than those during the light-polluted (4.3 m2 g−1) and clean periods (3.6 m2 g−1). To further evaluate the impact of individual chemical components of PM2.5 on light scattering, a multiple linear regression equation of measured bsp against the mass concentration of (NH4)2SO4, NH4NO3, Organic Matter (OM), EC, Fine Soil (FS), Coarse Matter (CM) and Other chemical compounds were performed. (NH4)2SO4, NH4NO3 and OM were the dominant species contributing to bsp under both dry and ambient conditions. OM contributed more to bsp than the sum of (NH4)2SO4 and NH4NO3 did under the dry condition during all the pollution periods and this was also the case under the ambient condition during the light-polluted and clean periods. However, the total contributions of (NH4)2SO4 and NH4NO3 to bsp under the ambient condition was 55%, much more than the 29% contribution from OM during the heavy-polluted period. High (NH4)2SO4 and NH4NO3 concentrations and their hygroscopicity were the main reasons causing visibility degradation during the heavy-polluted period, and the effect can be enhanced under high RH conditions.
Keywords: PM2.5; Aerosol size distribution; Hygroscopic growth; Biomass burning; Visibility degradation;

Non-culturable bioaerosols in indoor settings: Impact on health and molecular approaches for detection by Pascale Blais-Lecours; Phillipa Perrott; Caroline Duchaine (45-53).
Despite their significant impact on respiratory health, bioaerosols in indoor settings remain understudied and misunderstood. Culture techniques, predominantly used for bioaerosol characterisation in the past, allow for the recovery of only a small fraction of the real airborne microbial burden in indoor settings, given the inability of several microorganisms to grow on agar plates. However, with the development of new tools to detect non-culturable environmental microorganisms, the study of bioaerosols has advanced significantly. Most importantly, these techniques have revealed a more complex bioaerosol burden that also includes non-culturable microorganisms, such as archaea and viruses. Nevertheless, air quality specialists and consultants remain reluctant to adopt these new research-developed techniques, given that there are relatively few studies found in the literature, making it difficult to find a point of comparison. Furthermore, it is unclear as to how this new non-culturable data can be used to assess the impact of bioaerosol exposure on human health. This article reviews the literature that describes the non-culturable fraction of bioaerosols, focussing on bacteria, archaea and viruses, and examines its impact on bioaerosol-related diseases. It also outlines available molecular tools for the detection and quantification of these microorganisms and states various research needs in this field.
Keywords: Bioaerosols; Risk assessment; Culture-independent; Molecular methods; Virus; Archaea; Bacteria; Culturable microorganisms;

Evaluation of MEGAN predicted biogenic isoprene emissions at urban locations in Southeast Texas by Sri Harsha Kota; Gunnar Schade; Mark Estes; Doug Boyer; Qi Ying (54-64).
Summertime isoprene emissions in the Houston area predicted by the Model of Emissions of Gases and Aerosol from Nature (MEGAN) version 2.1 during the 2006 TexAQS study were evaluated using a source-oriented Community Multiscale Air Quality (CMAQ) Model. Predicted daytime isoprene concentrations at nine surface sites operated by the Texas Commission of Environmental Quality (TCEQ) were significantly higher than local observations when biogenic emissions dominate the total isoprene concentrations, with mean normalized bias (MNB) ranges from 2.0 to 7.7 and mean normalized error (MNE) ranges from 2.2 to 7.7. Predicted upper air isoprene and its first generation oxidation products of methacrolein (MACR) and methyl vinyl ketone (MVK) were also significantly higher (MNB = 8.6, MNE = 9.1) than observations made onboard of NOAA's WP-3 airplane, which flew over the urban area. Over-prediction of isoprene and its oxidation products both at the surface and the upper air strongly suggests that biogenic isoprene emissions in the Houston area are significantly overestimated. Reducing the emission rates by approximately 3/4 was necessary to reduce the error between predictions and observations. Comparison of gridded leaf area index (LAI), plant functional type (PFT) and gridded isoprene emission factor (EF) used in MEGAN modeling with estimates of the same factors from a field survey north of downtown Houston showed that the isoprene over-prediction is likely caused by the combined effects of a large overestimation of the gridded EF in urban Houston and an underestimation of urban LAI. Nevertheless, predicted ozone concentrations in this region were not significantly affected by the isoprene over-predictions, while predicted isoprene SOA and total SOA concentrations can be higher by as much as 50% and 13% using the higher isoprene emission rates, respectively.
Keywords: Community Multiscale Air Quality (CMAQ) model; Model of Emissions of Gases and Aerosols from Nature (MEGAN); Biogenic emissions; Isoprene; Source apportionment; 2006 TexAQS;

The global budgets of organic hydroperoxides for present and pre-industrial scenarios by M.A.H. Khan; M.C. Cooke; S.R. Utembe; P. Xiao; W.C. Morris; R.G. Derwent; A.T. Archibald; M.E. Jenkin; C.J. Percival; D.E. Shallcross (65-74).
The global 3-D chemistry-transport model, STOCHEM-CRI (Utembe et al., 2010), has been used to simulate the global distribution of organic hydroperoxides (ROOH) for both present day and pre-industrial scenarios. Globally, the formation of ROOH is solely from the reaction between RO2 and HO2, being more significant under NOx-limited conditions; here the self and cross reactions of RO2 and HO2 radicals dominate over their reaction with NO. The predominant global loss processes for ROOH are reaction with OH (95%) and by photolysis (4.4%) with a minor loss (<1%) by deposition, in the present day scenario. The associated global burden of ROOH in our model study is found to be 3.8 Tg. The surface distribution of ROOH shows a peak near the equator corresponding with higher photochemical activity and large (biogenic) VOC emissions. The simulated abundances of ROOH are comparable with those recorded in field campaigns, but generally show a tendency towards underestimation, particularly in the boundary layer. ROOH displayed seasonal cycles with higher concentrations during the summer months and lower concentrations during the winter months. The effects of including proposed HOx recycling schemes, including isomerisation of isoprene-derived peroxy radicals on the global budget of ROOH have also been investigated for the present and the pre-industrial environment. The present day simulations showed significant increases in CH3OOH and ROOH (up to 80% and 30%, respectively) over tropical forested regions, due to a general increase in HO2 and RO2 levels in isoprene-rich regions at low NOx levels. In the pre-industrial scenario, the increases in CH3OOH and total ROOH abundances are even larger, reflecting the more efficient operation of HOx recycling mechanisms at lower NOx levels. RCO3H species contribute 40–50% of the global burden of ROOH; inclusion of HOx recycling mechanisms leads to an increase in these RCO3H species but there is no discernible change in the remaining ROOH (ROOH–RCO3H) burden.
Keywords: Organic hydroperoxides; STOCHEM-CRI model; HOx recycling mechanism; Present day simulation; Pre-industrial scenario;

Ammonia losses and nitrogen partitioning at a southern High Plains open lot dairy by Richard W. Todd; N. Andy Cole; G. Robert Hagevoort; Kenneth D. Casey; Brent W. Auvermann (75-83).
Animal agriculture is a significant source of ammonia (NH3). Cattle excrete most ingested nitrogen (N); most urinary N is converted to NH3, volatilized and lost to the atmosphere. Open lot dairies on the southern High Plains are a growing industry and face environmental challenges as well as reporting requirements for NH3 emissions. We quantified NH3 emissions from the open lot and wastewater lagoons of a commercial New Mexico dairy during a nine-day summer campaign. The 3500-cow dairy consisted of open lot, manure-surfaced corrals (22.5 ha area). Lactating cows comprised 80% of the herd. A flush system using recycled wastewater intermittently removed manure from feeding alleys to three lagoons (1.8 ha area). Open path lasers measured atmospheric NH3 concentration, sonic anemometers characterized turbulence, and inverse dispersion analysis was used to quantify emissions. Ammonia fluxes (15-min) averaged 56 and 37 μg m−2 s−1 at the open lot and lagoons, respectively. Ammonia emission rate averaged 1061 kg d−1 at the open lot and 59 kg d−1 at the lagoons; 95% of NH3 was emitted from the open lot. The per capita emission rate of NH3 was 304 g cow−1 d−1 from the open lot (41% of N intake) and 17 g cow−1 d−1 from lagoons (2% of N intake). Daily N input at the dairy was 2139 kg d−1, with 43, 36, 19 and 2% of the N partitioned to NH3 emission, manure/lagoons, milk, and cows, respectively.
Keywords: Ammonia; Emissions; Dairy; Milk cows; Open lot; Inverse dispersion analysis;

Development of a land-use regression model for ultrafine particles in Toronto, Canada by Kelly Sabaliauskas; Cheol-Heon Jeong; Xiaohong Yao; Christopher Reali; Tim Sun; Greg J. Evans (84-92).
This study applies land-use regression (LUR) to characterize the spatial distribution of ultrafine particles (UFP) in a large city. Particle number (PN) concentrations were measured in residential areas around Toronto, Canada, between June and August 2008. A combination of fixed and mobile monitoring was used to assess spatial gradients between and within communities. The fixed monitoring locations included a central site, two downtown sites, and four residential sites located 6–15 km from the downtown core. The mobile data included average PN concentrations collected on 112 road segments from 10 study routes that were repeated on three separate days. The mobile data was used to create the land-use regression model while the fixed sites were used for validation purposes. The predictor variables that best described the spatial variation of PN concentration (R2 = 0.72, validated R2 = 0.68) included population density within 300 m, total resource and industrial area within 1000 m, total residential area within 3000 m, and major roadway and highway length within 3000 m. The LUR model successfully predicted the afternoon peak PN concentration (slope = 0.96, R2 = 0.86) but over-predicted the 24-h average PN concentration (slope = 1.28, R2 = 0.72) measured at seven fixed monitoring sites.
Keywords: Ultrafine particles; Diurnal variation; Spatiotemporal variation; Land use regression;

The dependence of nitro-organic compound emissions in automotive exhaust particles on the type of aftertreatment used was investigated. Three diesel vehicles with different aftertreatment systems (an oxidation catalyst, vehicle-DOC; a particulate matter and NO x reduction system, vehicle-DPNR; and a urea-based selective catalytic reduction system, vehicle-SCR) and a gasoline car with a three-way catalyst were tested. Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) and nitrophenols in the particles emitted were analyzed by thermal desorption gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry. The secondary production of nitro-organic compounds on the filters used to collect particles and the adsorption of gaseous nitro-organic compounds by the filters were evaluated. Emissions of 1-nitropyrene, 9-nitroanthracene, and 4-nitrophenol in the diesel exhaust particles were then quantified. The NO x reduction process in vehicle-DPNR appeared to remove nitro-hydrocarbons efficiently but not to remove nitro-oxygenated hydrocarbons efficiently. The nitro-PAH emission factors were lower for vehicle-DOC when it was not fitted with a catalyst than when it was fitted with a catalyst. The 4-nitrophenol emission factors were also lower for vehicle-DOC with a catalyst than vehicle-DOC without a catalyst, suggesting that the oxidation catalyst was a source of both nitro-PAHs and 4-nitrophenol. The time-resolved aerosol mass spectrometry data suggested that nitro-organic compounds are mainly produced when an engine is working under load. The presence of 4-nitrophenol in the particles was not confirmed statistically because of interference from gaseous 4-nitrophenol. Systematic errors in the estimated amounts of gaseous 1-nitropyrene and 9-nitroanthracene adsorbed onto the filters and the estimated amounts of volatile nitro-organic compounds that evaporated during sampling and during post-sampling conditioning could not be excluded. An analytical method in which all gaseous compounds are absorbed before particles are collected, and in which the volatile compounds are derivatized, would improve the precision and the accuracy of the data.
Keywords: Diesel exhaust particles (DEPs); Nitro-PAH; Nitrophenol; TD-GC/MS; LC/MS;

Multivariate analysis between driving condition and vehicle emission for light duty gasoline vehicles during rush hours by Liang Qu; Mengliang Li; Dong Chen; Kaibo Lu; Taosheng Jin; Xiaohong Xu (103-110).
Fourteen light-duty gasoline vehicles were tested by an OBS-2200 portable emission measurement system (PEMS). Vehicle speed, acceleration and emission rates of HC, CO, NOx and CO2 were recorded during rush hours (7:00–9:00 and 16:30–18:30 local time) in Tianjin, China. The emission factors of HC, CO and NOx for carbureted vehicles were 10, 4, 3 times higher than those with MPI (multi-points injection) and TWC (three-way catalytic converter), respectively. The emission factors of CO2 for carburetor car were 29% lower than those with MPI and TWC. For both types of vehicles, the Pearson correlation coefficients, between speed and CO2 emission in the mode of accelerating as well as between VSP (vehicle specific power) and CO2 emission when VSP > 0, remained relatively high (r > 0.5, p < 0.001) and stable. This high repeatability of correlation was also found for NOx in carburetor vehicles. Linear trends between emission rates and VSP (bin-averaged data) were observed for NOx and CO2 from MPI vehicles, and HC, NOx and CO2 from carburetor vehicles.Display Omitted
Keywords: Driving condition; Vehicle emission; Portable emission measurement system (PEMS); Vehicle specific power (VSP); Correlation analysis;

Historical trends and sources of TSP in a Sonoran desert city: Can the North America Monsoon enhance dust emissions? by Verónica Moreno-Rodríguez; Rafael Del Rio-Salas; David K. Adams; Lucas Ochoa-Landin; Joel Zepeda; Agustín Gómez-Alvarez; Juan Palafox-Reyes; Diana Meza-Figueroa (111-121).
In this work, the trends of total suspended particulate matter (TSP) were analyzed during a period of 12 years (2000–2012) on the basis of meteorological parameters. The results of historical trends of TSP show that post-monsoon dust emission seems to be connected to rainfall distribution in the urban environment. Particulate matter is dominated by plagioclase, quartz, calcite, and montmorillonite phases with barium sulfate, and particles enriched in Cu, Fe, and Ce. Elemental composition and principal component analysis allow the identification of two major sources for metals incorporated in geogenic dust: cement, and traffic. Geochemical analysis of non-mobile trace elements show a similar signature as local cement brands in TSP filters, but it remains unknown if such a signature is related to cement production, erosion of buildings, or construction activities. La–Ce geochemical tracers show that geogenic dust is an important media of transportation for traffic, and cement-related contaminants.This work highlights the importance of monsoon season precipitation in dust generation in arid urban environments, and it could contribute to regional studies including the southwestern US regarding the dust emission processes and transport of pollutants across the trans-boundary.
Keywords: North America Monsoon; Dust; Traffic; Cement; Principal component analysis;

Contribution of various microenvironments to the daily personal exposure to ultrafine particles: Personal monitoring coupled with GPS tracking by Gabriel Bekö; Birthe Uldahl Kjeldsen; Yulia Olsen; Jasper Schipperijn; Aneta Wierzbicka; Dorina Gabriela Karottki; Jørn Toftum; Steffen Loft; Geo Clausen (122-129).
Exposure to ultrafine particles (UFP) may have adverse health effects. Central monitoring stations do not represent the personal exposure to UFP accurately. Few studies have previously focused on personal exposure to UFP. Sixty non-smoking residents living in Copenhagen, Denmark were asked to carry a backpack equipped with a portable monitor, continuously recording particle number concentrations (PN), in order to measure the real-time individual exposure over a period of ∼48 h. A GPS logger was carried along with the particle monitor and allowed us to estimate the contribution of UFP exposure occurring in various microenvironments (residence, during active and passive transport, other indoor and outdoor environments) to the total daily exposure. On average, the fractional contribution of each microenvironment to the daily integrated personal exposure roughly corresponded to the fractions of the day the subjects spent in each microenvironment. The home environment accounted for 50% of the daily personal exposure. Indoor environments other than home or vehicles contributed with ∼40%. The highest median UFP concentration was obtained during passive transport (vehicles). However, being in transit or outdoors contributed 5% or less to the daily exposure. Additionally, the subjects recorded in a diary the periods when they were at home. With this approach, 66% of the total daily exposure was attributable to the home environment. The subjects spent 28% more time at home according to the diary, compared to the GPS. These results may indicate limitations of using diaries, but also possible inaccuracy and miss-classification in the GPS data.
Keywords: Ultrafine particles; Indoor/outdoor exposure; Active transport-physical activity; Passive transport-vehicles; Global Positioning System (GPS); Geographic Information System (GIS);

U.S. NO2 trends (2005–2013): EPA Air Quality System (AQS) data versus improved observations from the Ozone Monitoring Instrument (OMI) by Lok N. Lamsal; Bryan N. Duncan; Yasuko Yoshida; Nickolay A. Krotkov; Kenneth E. Pickering; David G. Streets; Zifeng Lu (130-143).
Emissions of nitrogen oxides (NO x ) and, subsequently, atmospheric levels of nitrogen dioxide (NO2) have decreased over the U.S. due to a combination of environmental policies and technological change. Consequently, NO2 levels have decreased by 30–40% in the last decade. We quantify NO2 trends (2005–2013) over the U.S. using surface measurements from the U.S. Environmental Protection Agency (EPA) Air Quality System (AQS) and an improved tropospheric NO2 vertical column density (VCD) data product from the Ozone Monitoring Instrument (OMI) on the Aura satellite. We demonstrate that the current OMI NO2 algorithm is of sufficient maturity to allow a favorable correspondence of trends and variations in OMI and AQS data. Our trend model accounts for the non-linear dependence of NO2 concentration on emissions associated with the seasonal variation of the chemical lifetime, including the change in the amplitude of the seasonal cycle associated with the significant change in NO x emissions that occurred over the last decade. The direct relationship between observations and emissions becomes more robust when one accounts for these non-linear dependencies. We improve the OMI NO2 standard retrieval algorithm and, subsequently, the data product by using monthly vertical concentration profiles, a required algorithm input, from a high-resolution chemistry and transport model (CTM) simulation with varying emissions (2005–2013). The impact of neglecting the time-dependence of the profiles leads to errors in trend estimation, particularly in regions where emissions have changed substantially. For example, trends calculated from retrievals based on time-dependent profiles offer 18% more instances of significant trends and up to 15% larger total NO2 reduction versus the results based on profiles for 2005. Using a CTM, we explore the theoretical relation of the trends estimated from NO2 VCDs to those estimated from ground-level concentrations. The model-simulated trends in VCDs strongly correlate with those estimated from surface concentrations (r = 0.83, N = 355). We then explore the observed correspondence of trends estimated from OMI and AQS data. We find a significant, but slightly weaker, correspondence (i.e., r = 0.68, N = 208) than predicted by the model and discuss some of the important factors affecting the relationship, including known problems (e.g., NO z interferents) associated with the AQS data. This significant correspondence gives confidence in trend and surface concentration estimates from OMI VCDs for locations, such as the majority of the U.S. and globe, that are not covered by surface monitoring networks. Using our improved trend model and our enhanced OMI data product, we find that both OMI and AQS data show substantial downward trends from 2005 to 2013, with an average reduction of 38% for each over the U.S. The annual reduction rates inferred from OMI and AQS measurements are larger (−4.8 ± 1.9%/yr, −3.7 ± 1.5%/yr) from 2005 to 2008 than 2010 to 2013 (−1.2 ± 1.2%/yr, −2.1 ± 1.4%/yr). We quantify NO2 trends for major U.S. cities and power plants; the latter suggest larger negative trend (−4.0 ± 1.5%/yr) between 2005 and 2008 and smaller or insignificant changes (−0.5 ± 1.2%/yr) during 2010–2013.
Keywords: Nitrogen dioxide; Troposphere; Air quality; Trend; Aura OMI;

Regional air quality impacts of hydraulic fracturing and shale natural gas activity: Evidence from ambient VOC observations by Timothy Vinciguerra; Simon Yao; Joseph Dadzie; Alexa Chittams; Thomas Deskins; Sheryl Ehrman; Russell R. Dickerson (144-150).
Over the past decade, concentrations of many anthropogenic pollutants have been successfully reduced, improving air quality. However, a new influx of emissions associated with hydraulic fracturing and shale natural gas operations could be counteracting some of these benefits. Using hourly measurements from Photochemical Assessment Monitoring Stations (PAMS) in the Baltimore, MD and Washington, DC areas, we observed that following a period of decline, daytime ethane concentrations have increased significantly since 2010, growing from ∼7% of total measured nonmethane organic carbon to ∼15% in 2013. This trend appears to be linked with the rapidly increasing natural gas production in upwind, neighboring states, especially Pennsylvania and West Virginia. Ethane concentrations failed to display this trend at a PAMS site outside of Atlanta, GA, a region without new widespread natural gas operations.
Keywords: Hydraulic fracturing; Ethane; Natural gas;

Plume mapping and isotopic characterisation of anthropogenic methane sources by G. Zazzeri; D. Lowry; R.E. Fisher; J.L. France; M. Lanoisellé; E.G. Nisbet (151-162).
Methane stable isotope analysis, coupled with mole fraction measurement, has been used to link isotopic signature to methane emissions from landfill sites, coal mines and gas leaks in the United Kingdom. A mobile Picarro G2301 CRDS (Cavity Ring-Down Spectroscopy) analyser was installed on a vehicle, together with an anemometer and GPS receiver, to measure atmospheric methane mole fractions and their relative location while driving at speeds up to 80 kph. In targeted areas, when the methane plume was intercepted, air samples were collected in Tedlar bags, for δ13C–CH4 isotopic analysis by CF-GC-IRMS (Continuous Flow Gas Chromatography-Isotope Ratio Mass Spectrometry). This method provides high precision isotopic values, determining δ13C–CH4 to ±0.05 per mil. The bulk signature of the methane plume into the atmosphere from the whole source area was obtained by Keeling plot analysis, and a δ13C–CH4 signature, with the relative uncertainty, allocated to each methane source investigated. Both landfill and natural gas emissions in SE England have tightly constrained isotopic signatures. The averaged δ13C–CH4 for landfill sites is −58 ± 3‰. The δ13C–CH4 signature for gas leaks is also fairly constant around −36 ± 2‰, a value characteristic of homogenised North Sea supply. In contrast, signatures for coal mines in N. England and Wales fall in a range of −51.2 ± 0.3‰ to −30.9 ± 1.4‰, but can be tightly constrained by region. The study demonstrates that CRDS-based mobile methane measurement coupled with off-line high precision isotopic analysis of plume samples is an efficient way of characterising methane sources. It shows that isotopic measurements allow type identification, and possible location of previously unknown methane sources. In modelling studies this measurement provides an independent constraint to determine the contributions of different sources to the regional methane budget and in the verification of inventory source distribution.
Keywords: Plume mapping; Methane isotopes; Picarro mobile;

Characterization of carbonaceous aerosols over the East China Sea: The impact of the East Asian continental outflow by Fengwen Wang; Zhigang Guo; Tian Lin; Limin Hu; Yingjun Chen; Yifang Zhu (163-173).
Seventy-five paired PM2.5 (aerodynamic diameter less than 2.5 μm) and TSP (total suspended particle) samples collected from a pristine island in the East China Sea (ECS) between October 2011 and August 2012 were analyzed for organic carbon (OC), elemental carbon (EC), and n-alkanes. The island lies in the pathway of continental outflow from Mainland China to the northwest Pacific Ocean driven by the East Asian Monsoon. The concentrations of OC, EC (in μg/m3), and n-alkanes (in ng/m3) were highest in winter (means: 4.7, 1.3, 140.1, respectively) and lowest in summer (means: 1.1, 0.3, 17.0, respectively). PM2.5 contained approximately 88% of the OC, 80% of the EC, and 61% of the n-alkanes in TSP. Petroleum residue was the dominant contributor to the n-alkanes. C12–C22 n-alkanes with strong even-to-odd predominance observed in winter were attributed to the microbial contribution from sea spray aerosol (SSA) driven by the higher wind speed. There was a higher secondary organic carbon (SOC)/OC ratio in warm seasons (summer and fall) than that in cold seasons (spring and winter). The dominance of primary organic carbon (POC) and EC in cold seasons was possibly mainly due to the influence of the East Asian continental outflow. Three episodes of high concentrations of carbonaceous aerosols were observed, and we focused on the impact of these pollutants from East Asia on the air quality over the ECS. Carbonaceous pollutants were more concentrated in PM2.5 during the fall episode triggered by biomass burning in East China. The winter haze associated with intensive indoor heating in North China brought substantial carbonaceous pollutants, with a minor influence on their size distribution. The dust episode in spring was related to coarse particles (i.e., TSP–PM2.5), yielding a distinctly different size distribution.
Keywords: Carbonaceous aerosols; Concentration; Size distribution; Sources; East Asian continental outflow; East China Sea;

Statistical analysis of PM2.5 observations from diplomatic facilities in China by Federico M. San Martini; Christa A. Hasenkopf; David C. Roberts (174-185).
Systematic monitoring of air quality are lacking in many parts of the world, especially in cities where air quality is poor. Since 2008, the U.S. Embassy in Beijing has been collecting real-time air-quality data from a monitor on the Embassy's rooftop and sharing that data publicly through social media. Using this freely available data, as well as those from four other U.S. consulates in China that are also now collecting and sharing data publicly, we demonstrate that rooftop air-quality monitors installed at embassies and consulates can further our understanding of air quality and provide a rich, hourly-averaged, long-term data source for the academic community and decision-makers. For example, this is the first study to present an analysis of diurnal variability of PM2.5 in Chengdu, Guangzhou, Shanghai, and Shenyang. We analyzed the diurnal variability of PM2.5 over the entire period of measurement for those cities and Beijing, and found marked variation across seasons and between cities. This dataset allows comparison of the PM2.5 annual average concentrations in 2013, with Guangzhou reporting 56.3 μg/m3, Shanghai 61.6 μg/m3, Chengdu 96.1 μg/m3, Beijing 99.6 μg/m3, and Shenyang 76.3 μg/m3 (note the average in Shenyang is from August 2013–July 2014). This study demonstrates the potential uses of air quality data that is currently systematically being collected and made publicly accessible by U.S. embassies and consulates in polluted but under-studied locations.
Keywords: PM2.5; Statistical analysis; Diplomatic facilities; Science policy;

The changes and long-range transport of PM2.5 in Beijing in the past decade by Lihui Han; Shuiyuan Cheng; Guoshun Zhuang; Hongbing Ning; Haiyan Wang; Wei Wei; Xiujuan Zhao (186-195).
A sampling campaign of PM2.5 in Beijing from 2002 to 2004 and from 2011 to 2013 was performed to investigate the changes of typical characteristics of PM2.5 at the representative city over Northern China in the past decade. A spring PM2.5 monitoring network was operated to study the long-range transport of PM2.5 in five cities along the pathway of dust storm across Northern and Eastern China in spring 2004. PM2.5 concentrations gradually decreased, but PM2.5 pollution still retained a high level and has been changed from dust type to haze-fog pollution at Beijing in the past decade. The seasonal variation of PM2.5 was spring > winter > autumn > summer during 2002–2004, but winter > autumn > summer > spring in 2011–2013. The mass concentration of mineral aerosol was in the order of spring > winter > summer > autumn, and reached the highest level in dust storm episodes during the past decade. Secondary inorganic aerosol (SIA) followed the order of summer > autumn > winter > spring during 2002–2004, however winter > autumn > summer > spring during 2011–2013, and reached the highest level in haze events. The concentrations of SO4 2−, NO3 and NH4 + of SIA displayed the order of SO4 2− > NO3  > NH4 + in haze days. SO4 2− concentrations in different seasons during 2011–2013 were almost lower than those in corresponding period in 2002–2004 respectively. But NO3 and NH4 + concentrations in autumn and winter of 2011–2013 were higher than those in 2002–2004. The OA and SOA concentrations followed the order of winter > autumn > summer and spring, and SOA was one of the significant components in OA. The secondary chemical transformation was the most significant source for PM2.5 during 2011–2013, compared with that in 2002–2004. Atmospheric pollution has exhibited severe complicated pollution. Dust storm carried not only large amounts of mineral dust, but also some secondary inorganic aerosol (SIA) and organic aerosol (OA), which would have significant impact on the wide downwind areas. The mass fraction of mineral aerosol decreased from the dust source to the downwind coastal sites, while those of secondary and carbonaceous components increased.
Keywords: PM2.5; Mineral aerosol; Secondary inorganic aerosol; Organic aerosol; Seasonal variation; Spatial distribution;