Atmospheric Environment (v.64, #C)

We evaluate the response to regional and latitudinal changes in aircraft NO x emissions using several climate metrics (radiative forcing (RF), Global Warming Potential (GWP), Global Temperature change Potential (GTP)). Global chemistry transport model integrations were performed with sustained perturbations in regional aircraft and aircraft-like NO x emissions. The RF due to the resulting ozone and methane changes is then calculated. We investigate the impact of emission changes for specific geographical regions (approximating to USA, Europe, India and China) and cruise altitude emission changes in discrete latitude bands covering both hemispheres. We find that lower latitude emission changes (per Tg N) cause ozone and methane RFs that are about a factor of 6 larger than those from higher latitude emission changes. The net RF is positive for all experiments. The meridional extent of the RF is larger for low latitude emissions. GWPs for all emission changes are positive, with tropical emissions having the largest values; the sign of the GTP depends on the choice of time horizon.► Global model study on climate response to regional/latitudinal aircraft NO x changes. ► RF impacts from O3 and CH4 are larger for changes at lower than at higher latitudes. ► GWPs for all latitudes are positive whereas the GTP can exhibit a change in sign.
Keywords: Aircraft emissions; Nitrogen oxides; Greenhouse gases; Radiative forcing; Climate metrics;

Adverse effect of outdoor air pollution on cardiorespiratory fitness in Chinese children by Yang Gao; Emily Y.Y. Chan; Yingjia Zhu; Tze Wai Wong (10-17).
Little is known about the health impact of air pollution on children's cardiovascular health. A cross-sectional study was conducted and data was analysed in 2048 Chinese schoolchildren (aged 8–10 years) in three districts of Hong Kong to examine the association between exposure to outdoor air pollution and cardiorespiratory fitness. Annual means of ambient PM10, SO2, NO2 and O3 from 1996 to 2003 were used to estimate individual exposure of the subjects. Cardiorespiratory fitness was measured for maximal oxygen uptake (VO2max), predicted by the multistage fitness test (MFT). Height and weight were measured and other potential confounders were collected with questionnaires. Analysis of covariance was performed to estimate the impact of air pollution on complete speed in the MFT and predicted VO2max. The results showed that children in high-pollution district had significantly lower complete speed and predicted VO2max compared to those in low- and moderate-pollution districts. Complete speed and predicted VO2max was estimated to reduce 0.327 km h−1 and 1.53 ml kg−1 min 1 per 10 μg m−3 increase in PM10 annual mean respectively, with those in girls being greater than in boys. Being physically active could not significantly result in improved cardiorespiratory fitness in polluted districts. The adverse effect seems to be independent of short-term exposure to air pollution. We concluded that long-term exposure to higher outdoor air pollution levels was negatively associated with cardiorespiratory fitness in Chinese schoolchildren, especially for girls. PM10 is the most relevant pollutant of the adverse effect. Elevated cardiorespiratory fitness observed in physically activate children could be negated by increased amount of inhaled pollutants during exercise.► VO2max is a strong predictor of cardiovascular and respiratory health. ► Little is known about adverse effect of ambient air pollution on children's VO2max. ► We found predicted VO2max reduced 1.53 ml kg−1 min−1 per 10 μg m−3 increase in PM10 annual mean. ► Exercise in highly-polluted areas could negate elevated VO2max of physical activity. ► There is a need of stricter air pollution control measures in China.
Keywords: Air pollution; Long-term effect; Cardiorespiratory fitness; Maximal oxygen uptake; Children;

Insights into the speciation of Sb in samples of brake linings, brake pad wear residues, road dust, and atmospheric particulate matter PM10 and PM2.5 were obtained combining several well established and advanced characterization techniques, such as scanning electron microscopy – energy dispersive spectrometry (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron radiation X-ray absorption spectroscopy (SR-XAS). The advantage of SR-XAS is that samples do not undergo any chemical treatment prior to measurements, thus excluding possible alterations. These analyses revealed that the samples of wheel rims dust, road dust, and atmospheric particulate matter are composed by an admixture of Sb(III) and Sb(V) in different relative abundances. Brake linings turned out to be composed by Sb(III) oxide (Sb2O3) and stibnite (Sb2S3). Stibnite was also detected in some of the particulate matter samples. The obtained data suggest that Sb2S3 during the brake abrasion process is easily decomposed forming more stable compounds such as antimony mixed oxidic forms. Sb redox speciation, in particular and well studied circumstances, may enhance the potential and selectivity of this element as a tracer of motor vehicle emissions in apportioning studies.► The analysed samples resulted heterogeneous with respect to the Sb chemical speciation. ► Stibnite (Sb2S3) was also found in some of the samples. ► Road traffic contributes significantly to the release of Sb into urban environment. ► Brake abrasion process decomposes Sb2S3 in more stable mixed oxidic forms. ► Sb appears very suitable as a tracer of road traffic in apportioning studies.
Keywords: XAS; XANES; EXAFS; Antimony; Particulate matter; Brake linings;

The transport and dispersion (T&D) models used for air-quality and defense applications require information describing the source parameters and meteorological conditions to forecast concentration and dosage fields. In many cases the source parameters are known and the meteorological conditions are based on observational data or mesoscale-model-generated forecast conditions. This research examines how errors in the input wind fields translate into uncertainty in the contaminant concentration predictions. In particular, this study focuses on street-level errors in the dispersion patterns that occur in “building aware” T&D models that are sensitive to urban designs (e.g. road and building patterns) and release locations relative to the buildings. This problem was evaluated by first creating a “truth” plume for a given release location and wind direction. Then the T&D model uncertainty associated with input wind errors were determined by comparing plumes calculated using wind directions varied at 2° increments to the truth plume. The uncertainty is quantified as fraction of overlap (FOO). The results are evaluated in a control simulation with no buildings, and in two commonly observed city designs (e.g. a regular grid, and hub and spoke configuration). The analysis examines both idealized building configurations along with the urban topography from cities that represent the regular grid and hub and spoke city designs. Results show that the relative impact of the uncertainty in the meteorological conditions and the corresponding sensitivity of the model to variations in the wind direction vary significantly with the release location and city designs. This suggests that some source locations are less (more) sensitive to uncertainty in meteorological conditions and that this information can be factored into the confidence that is placed in emergency response decisions based on this information.► We characterize the impact of wind direction uncertainties on dispersion solutions. ► The sensitivity is inversely related to the complexity in the topography. ► There is a broad range of model sensitivities to wind direction uncertainty.
Keywords: Urban transport and dispersion modeling; Emergency response; Meteorological uncertainty;

XAD-2 resin-based passive air samplers (PAS) were deployed for one year at eight cities in Mongolia, China, and South Korea to investigate the spatial distribution of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and dechlorane plus (DP). PCB levels were highly correlated with population size and density in China and South Korea. In Mongolia, PCB levels were relatively high considering the low population. In the cases of OCPs and DP, a country-specific distribution was observed. The highest levels of HCHs (hexachlorocyclohexane isomers) and DDTs (dichlorodiphenyl trichloroethane isomers) were detected at sites in China, whereas the highest endosulfan and DP levels were measured at South Korean sites. These results strongly reflected the patterns of use of these chemicals. Mirex, an insecticide never registered in Mongolia and South Korea, was detected at all sampling sites; this is likely to have resulted from long-range transport. Nevertheless, OCPs were generally low in Mongolia. This study confirms that PAS results reflect well the past and current usage of POPs in Northeast Asia.► XAD-2 resin-based PAS were deployed for one year in three Asian countries. ► The spatial distributions of PCBs, OCPs, and DP were investigated. ► Different distributions were observed among Mongolia, China, and South Korea.
Keywords: Persistent organic pollutants; Polychlorinated biphenyls; Organochlorine pesticides; Dechlorane plus; Passive air sampling; Northeast Asia; Long-range transport; PCB-11;

The adverse health effects of the release of hazardous substances into the atmosphere continue being a matter of concern, especially in densely populated urban regions. Emergency responders need to have estimates of these adverse health effects in the local population to aid planning, emergency response, and recovery efforts. For this purpose, models that predict the transport and dispersion of hazardous materials are as necessary as those that estimate the adverse health effects in the population.In this paper, we present the results obtained by coupling a Computational Fluid Dynamics model, FLACS (FLame ACceleration Simulator), with an exposure model, DDC (Damage Differential Coupling). This coupled model system is applied to a scenario of hypothetical release of chlorine with obstacles, such as buildings, and the results show how it is capable of predicting the atmospheric dispersion of hazardous chemicals, and the adverse health effects in the exposed population, to support decision makers both in charge of emergency planning and in charge of real-time response.The results obtained show how knowing the influence of obstacles in the trajectory of the toxic cloud and in the diffusion of the pollutants transported, and obtaining dynamic information of the potentially affected population and of associated symptoms, contribute to improve the planning of the protection and response measures.► The FLACS–DDC coupling represents a powerful tool for planning the emergency response in cities. ► The coupling provides a continuous monitoring of the affected regions. ► The coupling allows knowing the available time for a successful intervention.
Keywords: Emergency management planning; Hazardous materials; Acute exposure;

Spatio-temporal modelling of individual exposure to air pollution and its uncertainty by Lydia E. Gerharz; Otto Klemm; Anna V. Broich; Edzer Pebesma (56-65).
We developed a generic spatio-temporal model to quantify individual exposure to air pollution, using personal activity profiles derived from GPS and diaries, ambient air quality, and an indoor model. To enhance accessibility and reusability, the model approach is deployed as a web service. The model is applied to estimate personal exposure towards PM10 and PM2.5 for ten individuals in Münster, Germany. Modelled daily averages range for PM10 between 17 and 126 and between 6 and 84 μg m−3 for PM2.5. Comparison with personal monitoring data shows good agreement at temporal resolutions from 5 min to one day. Uncertainties in the model results are considerable and increase with higher exposure levels. Large deviations between modelled and measured exposure can often be explained by missing data on indoor emissions or insufficiently detailed activity diaries. The developed model allows the assessment of individual exposure with uncertainties on a high spatio-temporal resolution. By providing the methodology through a web service interface and using generic indoor parameter distributions, the model can be easily transferred to new application areas or could be provided for public use to identify hazardous exposure events.► We developed a generic individual spatio-temporal exposure model. ► The model shows good compliance with validation measurements. ► The model approximated exposure better than urban background station measurements. ► We provide the model functionality through an open web service interface.
Keywords: Exposure; Web service; GPS; PM10; PM2.5; Uncertainties;

Observations of atmospheric reactive nitrogen species in Rocky Mountain National Park and across northern Colorado by Katherine B. Benedict; Derek Day; Florian M. Schwandner; Sonia M. Kreidenweis; Bret Schichtel; William C. Malm; Jeffrey L. Collett (66-76).
Increasing rates of nitrogen deposition are a concern in many protected ecosystems. Understanding the sources influencing these regions can be a challenge as there are often few observations available to understand the transport of key species. Several field campaigns were conducted in and around Rocky Mountain National Park (RMNP) from 2006 to 2009 to assess the impacts of various reactive nitrogen sources and regional meteorology on reactive nitrogen deposition. Measurements of ammonia, ammonium, nitric acid, and nitrate at ground-level sites across northern Colorado were used to examine spatial gradients in atmospheric reactive nitrogen concentrations, the influence of wind direction on reactive nitrogen transport in the regional atmosphere, and anthropogenic contributions to reactive nitrogen concentrations in RMNP. The highest concentrations of reduced nitrogen occurred on the eastern plains of Colorado while oxidized nitrogen concentrations were highest along the Front Range urban corridor. Both regions lie east of RMNP. Upslope (easterly) winds associated with mountain–valley wind patterns and larger, synoptic scale forcing, transport emissions from these sources westward up the eastern slope of the Rockies and into RMNP; the highest ammonium and nitrate concentrations in RMNP were clearly associated with this upslope transport pattern. Concentrations of key reactive nitrogen species east of the Continental Divide in RMNP were, on average, more than 50% higher than those observed at a background site located west of the park, further indicating large contributions from sources east of the park. These observations highlight the need to focus on controlling reactive nitrogen emissions east of the park as part of ongoing efforts to reduce reactive nitrogen deposition in RMNP.► There are strong gradients in reactive nitrogen concentrations across Colorado. ► Reduced nitrogen concentrations are highest on the eastern plains of Colorado. ► Oxidized nitrogen concentrations are highest along the Front Range urban corridor. ► Upslope winds periodically transport emissions from source regions east of RMNP. ► Observations indicate there are large contributions of atmospheric nitrogen from sources east of the park.
Keywords: Atmospheric nitrogen; Regional transport; Rocky Mountain National Park; Nitrogen deposition;

Observation of new particle formation over a mid-latitude forest facing the North Pacific by Yuemei Han; Yoko Iwamoto; Tomoki Nakayama; Kimitaka Kawamura; Tareq Hussein; Michihiro Mochida (77-84).
The number size distributions of aerosol particles were measured using a scanning mobility particle sizer (SMPS) at a mid-latitude forest in Japan during 20–30 August 2010. Four days during the observation period experienced new particle formation (NPF) under the conditions of low condensation and coagulation sinks. The formation rate of new particles was calculated to be in the range between 0.2 and 1.0 cm−3 s−1 for the NPF events. The growth rates of the newly formed mode of aerosol particles ranged between 5.0 and 15.7 nm h−1. The backward air mass trajectories revealed that the NPF occurred in clean maritime air masses originated from the North Pacific, which is characterized with the low mass concentrations of aerosol components. The results from the classification analysis of backward air mass trajectories indicate that the maritime air mass conditions are frequent at this forest site and are primarily in summer season. Large increases in the number concentrations of accumulation mode particles (above 90 nm) were followed by the increased precipitation rates in the afternoon hours on the NPF event days. Therefore, the newly-formed particles would be involved in the convective cloud formation and precipitation over the studied region.► New aerosol particle formation was observed over a mid-latitude forest in Japan. ► The property of the aerosol during new particle formation is characterized. ► The significance of new particle formation is discussed.
Keywords: New particle formation; Formation rate; Growth rate; Maritime air mass; Biogenic aerosol;

Characterization of secondary organic aerosol particles using aerosol laser time-of-flight mass spectrometer coupled with FCM clustering algorithm by Mingqiang Huang; Liqing Hao; Xiaoyong Guo; Changjin Hu; Xuejun Gu; Weixiong Zhao; Zhenya Wang; Li Fang; Weijun Zhang (85-94).
Experiments for formation of secondary organic aerosol (SOA) from photooxidation of 1,3,5-trimethylbenzene in the CH3ONO/NO/air mixture were carried out in the laboratory chamber. The size and chemical composition of the resultant individual particles were measured in real-time by an aerosol laser time of flight mass spectrometer (ALTOFMS) recently designed in our group. We also developed Fuzzy C-Means (FCM) algorithm to classify the mass spectra of large numbers of SOA particles. The study first started with mixed particles generated from the standards benzaldehyde, phenol, benzoic acid, and nitrobenzene solutions to test the feasibility of application of the FCM. The FCM was then used to extract out potential aerosol classes in the chamber experiments. The results demonstrate that FCM allowed a clear identification of ten distinct chemical particle classes in this study, namely, 3,5-dimethylbenzoic acid, 3,5-dimethylbenzaldehyde, 2,4,6-trimethyl-5-nitrophenol, 2-methyl-4-oxo-2-pentenal, 2,4,6-trimethylphenol, 3,5-dimethyl-2-furanone, glyoxal, and high-molecular-weight (HMW) components. Compared to offline method such as gas chromatography–mass spectrometry (GC–MS) measurement, the real-time ALTOFMS detection approach coupled with the FCM data processing algorithm can make cluster analysis of SOA successfully and provide more information of products. Thus ALTOFMS is a useful tool to reveal the formation and transformation processes of SOA particles in smog chambers.► Formation of SOA from oxidation of 1,3,5-trimethylbenzene, OH, and NO x in chamber. ► ALTOFMS was used to measure the composition of SOA particles in real time. ► FCM algorithm was employed to classify the SOA mass spectra for the first time.
Keywords: Secondary organic aerosol; Aerosol laser time of flight mass spectrometry; Laser desorption/ionization; Fuzzy clustering (FCM) algorithm;

Trend analysis of atmospheric deposition data: A comparison of statistical approaches by Aldo Marchetto; Michela Rogora; Silvia Arisci (95-102).
Numerical simulation was used to compare the most used trend analysis techniques on data series of ionic concentrations in atmospheric deposition. The Seasonal Kendall Test (SKT) showed the highest power, which increased in particular when using original weekly data instead of pooling together the samples in monthly or yearly volume-weighted averages. The simulation also showed that differences in power among tests and pooling intervals would be negligible for data series longer than about 12 years.We tested these results using data from a network of bulk deposition samplers at nine forest sites in Italy, for which data have been available since 1998. These sites were selected in different forests, ranging from arid Mediterranean evergreen oak forest to rainy Alpine beech or spruce forests. The results showed relevant differences as regards the number of significant trends detected using different techniques and different data pooling, even for 13-year data series.The use of minimum–maximum autocorrelation factor analysis allowed a better interpretation of the data, showing the main trend shapes among stations and variables.► We used numerical simulation and deposition data to compare trend analysis techniques. ► The Seasonal Kendall Test showed the highest power. ► Its power was increased when using weekly data instead of pooling the samples.
Keywords: Trend; Atmospheric deposition; Kendall test;

Transport of PAN and NO y from different source regions to the Swiss high alpine site Jungfraujoch by Shubha Pandey Deolal; Johannes Staehelin; Dominik Brunner; Junbo Cui; Martin Steinbacher; Christoph Zellweger; Stephan Henne; Martin K. Vollmer (103-115).
The effect of intercontinental transport on measurements of nitrogen oxides (NO x ), peroxyacetyl nitrate (PAN) and reactive nitrogen species (NO y ) at the high altitude site Jungfraujoch (3580 m asl), Switzerland, was evaluated using a combination of backward trajectories and chemical filters (NO y to carbon monoxide (CO) ratio). Mixing ratios associated with air masses transported from the planetary boundary layers (PBL) of the three continental source regions Europe, North America, and Asia, and of free tropospheric origin were characterized. The analysis was applied to PAN, NO x and NO y measurements of the period 1997–1998, and to a period more than 10 years later covering several months in 2008 and 2009–2010. The results show that the mixing ratios of PAN, NO x and NO y are largest in air advected from the European PBL. In contrast to previous studies, our results indicate that the springtime maximum in PAN and NO y mixing ratios is largely attributable to air originating from the European PBL whereas air of free tropospheric origin and intercontinental transport contribute less significantly. PAN and NO y mixing ratios in air masses classified as free tropospheric are also highest in spring but substantially lower than those influenced by European PBL air. Air masses last influenced by the North American source region show considerably lower mixing ratios of nitrogen species than European air masses suggesting that a large fraction of NO y is removed during intercontinental transport probably due to washout of soluble species such as HNO3. The seasonal contributions from different source regions to PAN mixing ratios at Jungfraujoch were evaluated. The average European contribution is highest during the warm seasons with 47–57% in 1997–1998 and 61–69% in 2009–2010. The maximum contribution of North American air masses is also observed in the warm season and was about 5–7% in 1997–1998 and 6–10% in 2009–2010. Air from Asian source regions did not make a significant contribution due to the limited number of cases of direct transport from Asia, but when they occurred the air masses contained significant pollutant levels.► We evaluated the effect of intercontinental vs. regional transport on PAN, NO x & NO y . ► Springtime maximum in PAN and NO y is attributable to European PBL than other sources. ► Spring maximum caused by strong photochemical activity with enhanced vertical transport. ► North American air masses had about a factor 2 lower mixing ratios than the European PBL.
Keywords: Peroxyacetyl nitrate (PAN); Reactive nitrogen species (NO y ); Long range transport; Springtime maximum;

Gaseous mercury emissions from subtropical forested and open field soils in a national nature reserve, southwest China by Ming Ma; Dingyong Wang; Rongguo Sun; Yuanyuan Shen; Lixing Huang (116-123).
Total gaseous mercury flux measurements of forested and open field soils in the subtropical forest zones, in Chongqing, Southwestern China were monitored from April 2011 to March 2012 to provide insight into the characteristics of gaseous mercury flux with and without vegetation covers. Samples were collected from surfaces of forest and open field as the most representative terrestrial surfaces in Jinyun Mountain. Simultaneously meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, solar radiation were analyzed and variations of atmospheric GEM concentration were examined. The results showed that annual averaged fluxes from soil in the forest and open-air site were 14.23 ng m2 h−1 and 20.74 ng m2 h−1 respectively, with a clear seasonal variation for each surface. The soil surface displayed the largest difference between evening and daytime flux, particularly in spring and summer in open field surface (i.e., with low flux in evening (1.93 ng m2 h−1) to high flux in daytime (97.86 ng m2 h−1) in summer). GEM fluxes in the open-air site were positively correlated with solar irradiation and soil temperature, and inversely correlated with air humidity. In the forest site, GEM fluxes showed weaker correlation with meteorological variables. Based on the whole year experiments and field tests, it can be found that in some season (especially fall), the mercury emission fluxes were more highly dependent on solar radiation and less dependent on temperature. The regression results demonstrated that each surface displayed similar responses to time series change in meteorological parameters. A comparison between one year periods in the two sites showed much larger emission from the open field with forest conversion to bare soil.► Hg flux in forest and open field had a clear seasonal variation. ► At the forest site Hg flux showed weaker correlation with meteorological variable. ► Hg flux was highly dependent on solar radiation especially in fall. ► A comparison showed much larger emission from open field as conversing to bare soil.
Keywords: Land-use change; Subtropical forest areas; Mercury flux; Seasonal change; Diurnal rhythm;

Corrigendum to “Linking in-vehicle ultrafine particle exposures to on-road concentrations” [Atmos. Environ. 59C (2012) 578–586] by Neelakshi Hudda; Sandrah P. Eckel; Luke D. Knibbs; Constantinos Sioutas; Ralph J. Delfino; Scott A. Fruin (124).

A spatial ammonia emission inventory for pig farming by Boris Rebolledo; Antonia Gil; Javier Pallarés (125-131).
Atmospheric emissions of ammonia (NH3) from the agricultural sector have become a significant environmental and public concern as they have impacts on human health and ecosystems.This work proposes an improved methodology in order to identify administrative regions with high NH3 emissions from pig farming and calculates an ammonia density map (kg NH3–N ha−1), based on the number of pigs and available agricultural land, terrain slopes, groundwater bodies, soil permeability, zones sensitive to nitrate pollution and surface water buffer zones. The methodology has been used to construct a general tool for locating ammonia emissions from pig farming when detailed information of livestock farms is not available.► We propose a methodology to quantify NH3 emissions from pig farming. ► We calculate an ammonia emission density map from Aragon pig farms. ► We establish areas with low carrying capacity for new livestock farms.
Keywords: Ammonia; Swine waste; Inventory; Spatial distribution; Livestock emissions; Aragon; Spain;

Fungal contribution to size-segregated aerosol measured through biomarkers by Patrizia Di Filippo; Donatella Pomata; Carmela Riccardi; Francesca Buiarelli; Cinzia Perrino (132-140).
Fungal spores are the dominant biological component of air. Although ubiquitous in outdoor air, they are scarcely measured due to the inadequacy of measurement methods. The use of biomarkers as tools for the determination of fungal contribution to bioaerosol has often been suggested, and ergosterol, arabitol and mannitol have been associated to fungal spores as tracers. In the present paper, the fungal component of aerosol was studied at suburban/rural and at urban sites. Ergosterol, arabitol, and mannitol contents in airborne particulate matter, even at different sizes, were determined. Literature conversion factors and calculated conversion factors correlating ergosterol, arabitol, and mannitol masses to fungi mass were applied and compared to each other. The obtained fungal spore concentrations were different depending on the marker utilized both with the conversion factors found in literature and the calculated ones. Size-segregated marker distribution suggested different sources for the three tracers indicating ergosterol as the only reliable biomarker at our latitudes. The fungal spore concentrations were higher at the suburban/rural location and respectively inversely and directly proportional to temperature and relative humidity.► Fungi-containing aerosols were studied by means of chemical biomarkers. ► Ergosterol, arabitol, mannitol were used as tracers for fungal spores. ► Fungal component of aerosol was studied even at different sizes of PM10. ► Arabitol and mannitol can overestimate fungal spore concentrations in atmosphere. ► Ergosterol remains the only reliable biomarker.
Keywords: Bioaerosol; Fungal spores; Biomarkers; Arabitol; Mannitol; Ergosterol;

Carbon dioxide emission from temperate semiarid steppe during the non-growing season by Weiwei Chen; Benjamin Wolf; Xunhua Zheng; Zhisheng Yao; Klaus Butterbach-Bahl; Nicolas Brüggemann; Shenghui Han; Chunyan Liu; Xingguo Han (141-149).
Clarifying whether grazed semiarid steppe is a sink or source of carbon dioxide (CO2) requires accurate quantification of the annual net CO2 exchange between the ecosystem and the atmosphere. Previous studies have primarily focused on the growing season and on single grazing pattern. Carbon dioxide emission from the temperate semiarid steppe during the non-growing season and its responses to various grazing practices still remains uncertain. Using the chamber-based technique, we simultaneously determined the CO2 fluxes during the non-growing season at twelve grazed semiarid temperate steppe plots in Inner Mongolia and investigated the responses of CO2 emission to different grazing practices. The CO2 fluxes during the non-growing season were demonstrated to be significantly regulated by soil temperature and moisture contents. The cumulative CO2 emission during the non-growing season (October–April) amounted to 353 ± 26 kg C ha−1 on average (ranges: 180–484 kg C ha−1), significantly demonstrating decrease with increasing grazing intensity and increase with mean snow cover depth or mean surface soil moisture content. The empirical equations describing these significant relationships provide simple approaches to estimate the regional amounts of CO2 emission from temperate semiarid steppe during the non-growing season.► Soil temperature determined the seasonality of CO2 flux. ► The CO2 emission could occur at soil temperature of −5 °C at steppe. ► Grazing decreased total CO2 emission during the non-growing season.
Keywords: Steppes; CO2; Soil respiration; Net carbon exchange; Grazing; Non-growing season; Inner Mongolia;

Meteorology confounds the comparison of air quality data across time and space. This presents challenges, for example, to comparisons of pollutant concentration data obtained with mobile monitoring platforms on different days and/or locations within the same airshed. In part to address this challenge, we employed a classification and regression tree (CART) modeling approach that can serve as a useful and straightforward tool in such air quality studies, to determine the comparability of meteorological conditions between measurement days and locations as well as to compare primary pollutant concentrations corrected by meteorological conditions. Specifically, regression trees were developed to obtain representative concentrations of traffic-related primary air pollutants such as NOx and CO, based on meteorological conditions for 2007–2009 in the California South Coast Air Basin (SoCAB). The resulting regression trees showed strong correlations between the regression classifications developed for different pollutant metrics, such as daily CO and NO x maxima, as well as between monitoring sites. For the SoCAB, the most important meteorological parameters controlling primary pollutant concentrations were the mean surface wind speed, geopotential heights at 925 mbar, the upper air north–south pressure gradient, the daily minimum temperature, relative humidity at 1000 mbar, and vertical stability, in approximate order of importance. The value of developing a regression tree for a single season was also explored by performing CART analysis separately on summer data. Although seasonal classifications were similar to those developed from annual data, the standard deviations of the classification groups were somewhat reduced.► Regression trees for primary pollutants were created using a CART model. ► Primary pollutant levels are largely under control of meteorology in the SoCAB. ► The most important meteorological variables are wind speed and geopotential height. ► Spatial variances in pollutants are well correlated with meteorological conditions. ► CART analysis provides an effective tool for meteorological comparability.
Keywords: Primary pollutants; Meteorological adjustment; Traffic emissions; Meteorological comparisons;

Observation of new particle formation and growth events in Asian continental outflow by Yumi Kim; Soon-Chang Yoon; Sang-Woo Kim; Kwang-Yul Kim; Han-Cheol Lim; Jegyu Ryu (160-168).
This study is based on 3-year continuous measurements (January 2008–December 2010) of aerosol number size distributions recorded with a Scanning Mobility Particle Sizer (SMPS) at two regional background stations, Gosan Climate Observatory (GCO) and Korea Global Atmosphere Watch Center (KGAWC), in Korea. We identified new particle formation and growth (NPF) events by applying the Cyclostationary Empirical Orthogonal Function (CSEOF) technique to aerosol number size distributions. Based on the first mode loading vectors and the corresponding principle components in the CSEOF analysis, we classified strong, weak, and non NPF days. A strong NPF event was observed on 7.5% of days (60 days out of a total 800 days) at GCO and on 14.6% of days (140 days out of a total 958 days) at KGAWC. The maximum occurrence of strong NPF events was reported in spring at GCO, but in winter at KGAWC. Only 16 of these days were considered as simultaneous NPF events, and 7 days were identical NPF events. The airmass history analysis on simultaneous NPF days indicated the NPF events to be associated with a fast-moving cold and dry airmass from the Asian continent after the passage of a frontal system. The particle formation rate (FR) and growth rate (GR) were estimated to be 1.44 (1.20) cm−3 s−1 and 4.4 (4.7) nm h−1, respectively, at GCO and KGAWC (in parentheses). Almost identical values for the condensation sink were estimated in strong NPF (8.3 × 10−3 s−1) and non NPF (8.2 × 10−3 s−1) events at GCO, whereas the condensation sink for strong NPF days (8.5 × 10−5 s−1) was lower than that of non NPF days (1.1 × 10−2 s−1) at KGAWC. The FR, GR, condensation sink, and vapor source rate at both GCO and KGAWC were lower than those reported in polluted urban areas, but higher than those at clean sites.► Investigate new particle formation and growth (NPF) events from 3-year measurements. ► Identify NPF events by applying CSEOF technique to aerosol number size distributions. ► A strong NPF event was observed on 7.5% (14.6%) of days at GCO (KGAWC). ► Only 16 days were considered as simultaneous NPF events between GCO and KGAWC.
Keywords: Particle formation; Growth rate; CSEOF; SMPS; Gosan;

Air quality variability near a highway in a complex urban environment by Richard W. Baldauf; David Heist; Vlad Isakov; Steven Perry; Gayle S.W. Hagler; Sue Kimbrough; Richard Shores; Kevin Black; Laurie Brixey (169-178).
In response to growing public health concerns regarding elevated air pollutant exposures and adverse human health effects for near-road populations, a study was conducted to assess how complex urban roadway configurations affect local-scale air quality. This study combined fixed-site and mobile air quality measurements with laboratory wind tunnel experiments to examine how the transport and dispersion of traffic-emitted pollutants varies with changing roadway configuration, notably with at-grade and cut section designs. Results of the study indicated that short-term maximum concentrations occurred with measurements made along at-grade locations, however, average concentrations tended to be higher at the top of the cut section compared with the at-grade location, most often occurring during lower air pollutant events. Wind flow and NO2/NO x ratios indicated that the cut section moderated peak concentrations through increased transport and dispersion, as well as reducing the influence of turbulence from vehicle activity near the road. The at-grade locations also experienced a higher impact from primary vehicle emissions than those measurements made at similar distances along a cut section. Mobile monitoring suggested that these peak concentrations quickly conformed to concentration levels measured near cut sections within 50–100 m of the source highway. Wind tunnel simulations of the study site with and without the cut section present indicated that the cut section reduced the concentrations of primary emitted vehicle pollutants by 15–25 percent for receptors located approximately 20 m from the highway. The wind tunnel simulations also revealed that buildings and other urban features influenced local-scale pollutant transport and need to be considered when evaluating near-road air quality.► We measure and model CO and NO2 pollutant concentrations along a complex urban highway. ► Peak concentrations occurred with at-grade design, averages higher with cut section. ► Wind tunnel showed 15–25% decrease for perpendicular winds with cut sections. ► Complexity of road design highly influenced near-road concentrations. ► The results show how urban features influence near-road population exposures.
Keywords: Air quality; Near-road; Traffic; Cut section highway; Wind tunnel assessment;

Carbon monoxide (CO) is an important greenhouse gas that is emitted during the incomplete combustion of biomass burning. In this study, we assessed the Measurements Of Pollution In the Troposphere (MOPITT) CO retrievals from two different biomass burning regions, fires in the evergreen forests of Northeast India and agriculture residue fires, Punjab, India. We analyzed long-term trends (2003–2011) in CO retrievals and fire–CO relationships including CO profiles at nine different atmospheric levels. Over a ten year period, the mean monthly CO for Northeast India ranged from 140.86 ppmv (−1σ) to 348.85 ppbv (+1σ) with a mean CO of 244.85 ppbv. We observed a clear increase in CO signal from February to March followed by a decrease in May coinciding with the fire signal. In Punjab, the mean monthly CO ranged from 158.21 ppbv (−1σ) to 286.40 ppbv (+1σ) with a mean CO of 222.30 ppbv. Comparison of mean CO during the peak fire months suggested relatively higher CO (439.06 ppbv) during March (evergreen forest burning) than October (194.83 ppbv) agricultural residue burning. We found MODIS fire radiative power (FRP) as a stronger predictor of surface CO signal than the fire counts in the evergreen forest fires. The segmented regression model fitted using nine years of FRP–CO data was useful in finding the FRP threshold impact on CO concentrations in the evergreen forests. To explain the low correlation between fires and MOPITT CO signal from the agricultural residue fires, we used the CALIPSO data to infer the smoke plume heights. Results suggested an average smoke plume height of 2.2 km during the peak biomass burning month from agricultural fires, compared to 4.61 km from evergreen forest fires. Overall, the MODIS FRP and CALIPSO data were useful in understanding the MOPITT CO sensitivity to fires.► Satellite data revealed significant CO pollution from forest burning. ► Fire radiative power (FRP) was found to be a better indicator of CO emissions than fire counts. ► Segmented regression was useful in identifying the FRP threshold impacting forest CO emissions. ► CALIPSO data revealed low smoke plume heights for agriculture fires than forest fires.
Keywords: Forest and agriculture residue fires; Carbon monoxide; Fire radiative power;

Emissions of trace gases and particles ≤2.5 microns aerodynamic diameter (PM2.5) from fires during 2008–2011 on the North Carolina coastal plain were collected and analyzed. Carbon mass balance techniques were used to quantify emission factors (EFs). PM2.5 EFs were at least a factor of 2 greater than those from forest burning of above-ground fuels because of extended smoldering combustion of organic soil layers and peat fuels. This is consistent with CO2 EFs at the low end of previously reported ranges for biomass fuels, indicating less efficient combustion and enhanced emissions of products of incomplete combustion (PICs). CO EFs are at the high end of the range of previously published EFs for smoldering fuels. The biomass burning tracer levoglucosan was found to compose 1–3 percent of PM2.5 from the organic soil fires, similar to fractions measured in smoke from above-ground fine fuels reported in previous studies. Organic soil fuel loads and consumption are very difficult to estimate, but are potentially as high as thousands of tonnes ha−1. Combined with higher emission factors, this can result in emission fluxes hundreds of times higher than from prescribed fires in above-ground fuels in the southeastern US. Organic soil fuel represents a source of particles and gases that is difficult to control and can persist for days to months, jeopardizing human health and incurring considerable costs to monitor and manage. Extended fires in organic soils can contribute substantially to PM2.5 on CO emission inventories and may not be adequately accounted for in current estimates.► PM2.5 EFs were at least a factor of 2 greater than those from above-ground fuels. ► CO EFs (250–300 g kg−1 fuel dry weight) are at the high end of the range of previously published EFs. ► Levoglucosan was found to compose 1–3 percent of PM2.5 from the organic soil fires. ► PM2.5 emissions may account for 10–20% of the total U.S. PM2.5 air emission inventory.
Keywords: Biomass burning; Organic soil; North Carolina; PM2.5; CO2; CO; Levoglucosan;

Highly time-resolved carbonaceous aerosol characterization in Yangtze River Delta of China: Composition, mixing state and secondary formation by Xiao-Feng Huang; Lian Xue; Xu-Dong Tian; Wei-Wei Shao; Tian-Le Sun; Zhao-Heng Gong; Wei-Wei Ju; Bing Jiang; Min Hu; Ling-Yan He (200-207).
The Yangtze River Delta (YRD) region is one of the most economically developed regions of China and characterized by high level of urbanization, which comes with the consequence of severe deterioration of its atmospheric environment in a large regional scale. In order to characterize the fine particle pollution features representative for YRD, especially for the abundant and complex carbonaceous component, we deployed advanced on-line measurement at a regional site in Jiaxing in the central YRD area during June 29–July 15 (the summer campaign) and December 11–23 (the winter campaign), with a high resolution aerosol mass spectrometer (AMS) and a single particle soot photometer (SP2). The mean PM1 mass concentration was observed to be 32.9 μg m−3 in summer, with organic matter (OM) and black carbon (BC) contributing 32.1 and 9.1%, respectively, and 41.9 μg m−3 in winter, with OM and BC contributing 30.3 and 16.9%, respectively. The O/C ratio of OM, an indicator for the oxidation level of organic aerosol, was calculated to be 0.28 in summer and 0.33 in winter, and the number fraction of internally mixed BC particles (NIB), an indicator for the aging level of BC, was calculated to be 0.51 in summer and 0.53 in winter. Two popular independent methods were used to estimate the amount of secondary organic aerosol (SOA) in Jiaxing: one is the positive matrix factorization method utilizing the high resolution aerosol mass spectra (the AMS-PMF method), and the other is the simple OC/EC ratio method (the OC/EC method). The AMS-PMF method estimated that SOA averagely accounted for 68.3 and 30.2% of OM in summer and winter, respectively. The SOA amount estimated by the OC/EC method was found to agree well with that by the AMS-PMF method in summer, but strong biomass burning events in winter made the OC/EC method over-estimate SOA largely. The seasonal variation of SOA indicates that SOA production in YRD is more determined by ambient temperatures than by precursors.► Fine particles were studied by advanced on-line techniques in Yangtze River Delta. ► Biomass burning was found to be a key factor influencing the air quality in winter. ► Secondary organic aerosol was estimated by two popular and independent methods.
Keywords: Yangtze River Delta (YRD); Organic aerosol; Black carbon; Secondary organic aerosol (SOA);

In order to study dust aerosol assimilation and radiative forcing in modeling East Asian dust aerosols and their impacts on the regional atmosphere, a three-dimensional variational data assimilation (3DV) and an aerosol radiative feedback scheme (RAD) are online implemented into a mesoscale numerical weather prediction system GRAPES/CUACE_Dust. Four modeling experiments are conducted: one control running (CTL) excluding 3DV and RAD as well as three sensitive running experiments respectively with 3DV, RAD, the integrated 3DV and RAD (3DV_RAD). The results indicate the 3DV-running shows a distinct improvement in the daily averaged dust concentrations, while the 3DV_RAD performs the better modeling during strong dust storms. The comparisons of the model bias for air temperature, pressure and wind speed from the CTL, RAD, and 3DV_RAD experiments present that the dust direct radiation leads to decreases in the lower tropospheric temperature and increases in the upper tropospheric temperature, which results in enhancing air pressure in the lower troposphere and declining air pressure in the upper troposphere. The 3DV_RAD modeling in the middle and upper troposphere is more reasonable than the RAD modeling, which suggests the importance of integration of aerosol assimilation and radiation forcing in modeling aerosols and meteorological fields.► 3DV improves modeling dust concentration and 3DV_RAD further corrects the modeling. ► 3DV_RAD is more efficiency in enhancing model ability in upper air meteorological fields than that in low and surface. ► Dust radiative feedback is negative at daytime and positive at night time.
Keywords: Dust radiative feedbacks; Aerosol assimilation system; Mesoscale dust forecast system;

Physical properties, chemical composition, sources, spatial distribution and sinks of indoor aerosol particles in a university lecture hall by I. Salma; K. Dosztály; T. Borsós; B. Söveges; T. Weidinger; G. Kristóf; N. Péter; Zs. Kertész (219-228).
PM10 mass, particle number (N) and CO2 concentrations, particle number size distributions and meteorological parameters were determined with high time resolution, and daily aerosol samples were collected in the PM10–2.0 and PM2.0 size fractions for chemical analysis in the middle of a university lecture hall for one week. Median concentrations for the PM10 mass and N of 15.3 μg m−3 and 3.7 × 103 cm−3, respectively were derived. The data are substantially smaller than the related outdoor levels or typical values for residences. There were considerable concentration differences for workdays, weekends and various lectures. Main sources of PM10 mass include the usage of chalk sticks for writing, wiping the blackboard, ordinary movements and actions of students and cleaning. High PM10 mass concentration levels up to 100 μg m−3 were realised for short time intervals after wiping the blackboard. The mass concentrations decreased rapidly after the emission source ceased to be active. Two classes of coarse particles were identified. General indoor dust particles exhibited a residence time of approximately 35 min, while the residence time for the chalk dust particles was approximately 20 min as lower estimates. Emission source rate for wiping the blackboard was estimated to be between 8 and 14 mg min−1. This represents a substantial emission rate but the source is active only up to 1 min. Suspension of the chalk (made mainly of gypsum) dust particles was confirmed by enrichment of Ca and S in the hall with respect to ambient urban aerosol. Contribution of ambient aerosol via the heating, ventilation and air conditioning (HVAC) facility was considerable for time intervals when the indoor sources of PM10 mass were not intensive. The HVAC facility introduces, however, the major amount of aerosol particles from the outdoors as far as their number concentration is regarded. Mean contribution of ultrafine particles to the total particle number was (69 ± 7)%, which is smaller than for the related outdoor urban environment. This can indicate aged ultrafine aerosol. The major amounts of CO2 arrive from the corridors through open doors by infiltration. Spatial distribution of the PM10 mass concentration within the hall was derived by CFD modelling, and spatial inhomogeneities were obtained.► The main source of PM10 mass was wiping the blackboard with an emission rate of 11 mg min−1. ► Two classes of coarse particles were identified with residence times of 35 and 15 min. ► Aerosol particles were introduced from the outdoors as far as their number is concerned. ► The major amounts of CO2 arrived from the corridors through open doors by infiltration. ► Spatial distribution of PM10 particles within the hall was rather inhomogeneous.
Keywords: Emission source rate; Residence time; Chemical composition; Enrichment factor; Indoor dust particles; Ultrafine particles;

Analysis of long-range transport of aerosols for Portugal using 3D chemical transport model and satellite measurements by O. Tchepel; J. Ferreira; A.P. Fernandes; S. Basart; J.M. Baldasano; C. Borrego (229-241).
The objective of this work is to assess the contribution of long-range transport of mineral dust from North Africa to the air pollution levels in Portugal based on a combination of a modelling approach and satellite observations. The Comprehensive Air Quality Model (CAMx) was applied together with the updated Dust REgional Atmospheric Model (BSC-DREAM8b) to characterise anthropogenic and natural sources of primary aerosols as well as secondary aerosols formation. The modelling results, after their validation and bias removing process, have been used in combination with aerosol measurements provided by Ozone Monitoring Instrument (OMI), using OMAERUV Level-2 v003 product, aiming to better understand the advantages and shortcomings of both, satellite and modelling aerosol data.The data analysis is presented for Portugal for July 2006 focusing on aerosol optical depth (AOD) at 500 nm and aerosol type. Based on the modelling results, the importance of the long-range transport of mineral dust was demonstrated for the simulation days, achieving a 60% contribution to AOD levels. The mineral dust is affecting atmospheric layers up to 6 km but peak concentrations are presented at layers below 2 km. The model predicts a complex mixture of different types of aerosol for the pixels classified by OMI as “mineral dust” and “sulphates”. Although a good agreement between the model outputs and OMI observations has been found in terms of the spatial pattern and AOD correlation is about 0.48 for mineral dust, several problems were identified. The model is systematically underestimating the aerosol concentration at near ground level in comparison with the air quality monitoring stations, while OMI is in general overestimating AOD for the analysed period based on the comparison with AERONET data. Additionally, misclassification of mineral dust for some geographical locations and discontinuity in AOD values along the coastal line at water/land interface in the OMI data are discussed.► The contribution of long-range transport of mineral dust from Africa is investigated. ► A combined approach based on satellite data and modelling is implemented. ► Aerosol composition from model is compared with the aerosol types from satellite data. ► The mineral dust affects vertical layers up to 6 km and contributes up to 60% in AOD. ► Possible misclassification and discontinuity at coast line in satellite data are stressed.
Keywords: Mineral dust; Aerosol optical depth; Satellite data; Chemical transport model;

Atmospheric deposition and canopy exchange of anions and cations in two plantation forests under acid rain influence by Weijun Shen; Huili Ren; G. Darrel Jenerette; Dafeng Hui; Hai Ren (242-250).
Acid deposition as a widely concerned environmental problem in China has been less studied in plantation forests compared to urban and secondary forests, albeit they constitute 1/3 of the total forested areas of the country. We measured the rainwater amount and chemistry outside and beneath the canopies of two widely distributed plantations (Acacia mangium and Dimocarpus longan) in the severe acid rain influenced Pearl River Delta region of southeastern China for two years. Our results showed that the frequency of acid rain was 96% on the basis of pH value <5.6. The volume-weighted mean (vwm) pH was 4.62 and higher in the dry (Oct.–Mar.) than in the wet (Apr.–Sep.) seasons. The major acidic anion was sulfate with vwm concentration of 140 μeq l−1 and annual deposition flux of 110.3 kg ha−1 yr−1. The major neutralizing cations were calcium (94.8 μeq l−1 and 28 kg ha−1 yr−1) and ammonium (41.2 μeq l−1 and 11.7 kg ha−1 yr−1). Over 95% of these major acidic anions and neutralizing cations were derived from anthropogenic and terrestrial sources as a result of industrial, agricultural and forestry activities. Plantation canopy had marked impacts on rainwater chemistry, with the measured anion and cation concentrations being significantly enriched in throughfall (TF) and stemflow (SF) rainwater by 1.4 (for NO 3 − ) to 20-fold (for K+) compared to those in bulk precipitation (BP). Dry deposition generally contributed about 13–22% of the total deposition while canopy leaching mainly occurred for K+ (>88%) and NH 4 + (10–38%). The two tree species showed distinct impacts on rainfall redistribution and rainwater chemistry due to their differences in canopy architecture and leaf/bark texture, suggesting that species-specific effects should not be overlooked while assessing the acid deposition in forested areas.► Sulfate is the major acidic anion while calcium and ammonium are the major neutralizing cations. ► Ion concentrations are enhanced by 1.4–20-fold after passing through plantation canopies. ► Coarser-textured tree leaves and barks are more capable of retaining acidic precursors. ► Acid rain is more severe in dry than in wet seasons.
Keywords: Atmospheric deposition; Acid rain; Canopy exchange; Plantation forest;

Organic, elemental and water-soluble organic carbon in size segregated aerosols, in the marine boundary layer of the Eastern Mediterranean by A. Bougiatioti; P. Zarmpas; E. Koulouri; M. Antoniou; C. Theodosi; G. Kouvarakis; S. Saarikoski; T. Mäkelä; R. Hillamo; N. Mihalopoulos (251-262).
To assess the origin and transformation of carbonaceous material in the marine boundary layer of the Eastern Mediterranean, a total of 111 size segregated aerosol samples have been collected using a 12-stage Small-Deposit-area low-volume-Impactor (SDI) covering an almost 3 year period. The samples have been analyzed for organic (OC), elemental (EC), water-soluble organic carbon (WSOC) and ionic components. Maxima of OC, EC and WSOC mass size distributions were found in the accumulation mode (0.449 μm) with occasionally a minor, secondary peak in the coarse mode (2.68 μm). OC and WSOC concentrations peak during summertime due to photochemistry, while EC during autumn, and spring. In general, almost 2/3 of OC and EC concentrations are found in the PM1 fraction of the aerosol with OC being mostly secondary and therefore highly oxidized and water-soluble to a great extent (∼70%). Using the EC-tracer method, it was found that 83 ± 11% of the PM10 organic carbon is secondary, with the percentage reaching ∼70% for the PM1 fraction, a value in very good accordance to WSOC/OC ratio. Ammonium sulfate accounts for 75.5 ± 21.7% and 9.3 ± 1.9% of the aerosol mass in the fine and coarse fraction respectively, exhibiting maximum concentrations also in the accumulation mode. It was estimated that, on average, sea salt and mineral dust account for 33% and 45% of the coarse inorganic mass fraction, respectively.► Carbonaceous aerosol constitutes a significant part of submicron mass fraction. ► Size distribution of OC, EC, WSOC and ions was performed during a 3 year period. ► OC, EC and WSOC exhibit bimodal distribution with maximum in the accumulation mode. ► 83.5 ± 11% of the PM10 OC is secondary. ► 70% of the fine mode OC is water-soluble with high summer and low winter values.
Keywords: Size distribution; Organic carbon; Water-soluble organic carbon; Chemical composition; Marine boundary layer; Eastern Mediterranean;

Hygroscopic growth of urban aerosol particles during the 2009 Mirage-Shanghai Campaign by Xingnan Ye; Chen Tang; Zi Yin; Jianmin Chen; Zhen Ma; Lingdong Kong; Xin Yang; Wei Gao; Fuhai Geng (263-269).
The hygroscopic properties of submicrometer urban aerosol particles were studied during the 2009 Mirage-Shanghai Campaign. The urban aerosols were composed of more-hygroscopic and nearly-hydrophobic particles, together with a trace of less-hygroscopic particles. The mean hygroscopicity parameter κ of the more-hygroscopic mode varied in the range of 0.27–0.39 depending on particle size. The relative abundance of the more-hygroscopic particles at any size was ca. 70%, slightly increasing with particle size. The number fraction of the nearly-hydrophobic particles fluctuated between 0.1 and 0.4 daily, in accordance with traffic emissions and atmospheric diffusion. The results from relative humidity dependence on hygroscopic growth and chemical analysis of fine particles indicated that particulate nitrate formation through the homogenous gas-phase reaction was suppressed under ammonia-deficient atmosphere in summer whereas the equilibrium was broken by more available NH3 during adverse meteorological conditions.► The urban aerosols are mainly composed of two mode particles. ► Aerosol hygroscopicity in Shanghai differs from other sites. ► NH4NO3 formation is suppressed in summer except that transport NH3 is available.
Keywords: Hygroscopicity; Urban aerosol; HTDMA; Yangtze River Delta;

Heterogeneous photochemical aging of soot by NO2 under simulated sunlight by Chong Han; Yongchun Liu; Hong He (270-276).
The aging process of soot in the atmosphere can significantly influence its physical and chemical properties. Here, the heterogeneous photochemical aging of soot by NO2 under simulated sunlight was investigated using in situ attenuated total internal reflection infrared spectroscopy. It was observed that simulated sunlight can enhance the aging process of soot by NO2. The photochemistry of soot with NO2 led to the formation of various nitro compounds and oxygen-containing species on the soot surface. The photolysis of the surface nitro compounds resulted in various carbonyl groups and gas-phase NO and HONO. The photochemical aging depended on the NO2 concentrations and combustion conditions of soot production. The soot samples with high content of organic carbon (OC) showed high photochemical reactivity towards NO2. This means that the active species mainly belong to OC components, which mainly consist of various polycyclic aromatic hydrocarbons (PAHs) and some unidentified components.► Sunlight can enhance the photochemical aging process of soot by NO2. ► Formed nitro compounds can be photolyzed and produce carbonyl species, NO and HONO. ► Combustion conditions can modify photo-reactivity of soot to NO2. ► Organic carbon provides main active sites to photochemical aging of soot by NO2.
Keywords: Soot; NO2; Organic carbon; Nitro compounds; Photochemical aging;

Characteristics and ship traffic source identification of air pollutants in China's largest port by Minjiang Zhao; Yan Zhang; Weichun Ma; Qingyan Fu; Xin Yang; Chunlei Li; Bin Zhou; Qi Yu; Limin Chen (277-286).
To characterize the air pollutants in Shanghai Port and identify the contribution from ship traffic emission, field measurements have been conducted in 2011. The trace gases SO2, NO2 and O3 were monitored and aerosol samples of TSP, PM2.5 and size-segregated particles were collected in a working area of Shanghai Port. Elements including V, Ni, Al, Fe, Si, Ca, Na, Mg, Mn, Zn, Co, Cr in aerosol samples and heavy fuel oil samples were analyzed. The results revealed that average hourly SO2 and NO2 concentrations in Shanghai Port were respectively 29.4 and 63.7 μg m−3, average daily concentrations of TSP and PM2.5 were 114.39 and 62.60 μg m−3, comparable with the ones in Shanghai land area. Ni and V were found enriched in fine particles with averaged concentrations of 80.0 and 14.8 ng m−3 in PM2.5 respectively. Also ratio of V/Ni in aerosol under summertime airflow was 3.4, very close to the ratio of averaged V and Ni content in international heavy fuel oils used in Shanghai Port. The backward trajectory analysis further revealed that SO2, NO2, and V under coastal airflows were mainly from ship traffic emission. The mean concentration of V was 15.84 ng m−3 under hybrid coastal airflows, much higher than that of 9.84 ng m−3 under continental airflows. Furthermore, V was found to be highly correlated with ship fluxes, and was selected as an indicator of ship traffic emission in Shanghai. The estimated primary PM2.5 contribution from ship traffic ranged from 0.63 to 3.58 μg m−3, with an average of 1.96 μg m−3. This PM2.5 fraction accounted for 4.23% of the total PM2.5 in an average level, and reached to a maximum of 12.8%. Furthermore, there could be 64% of primary PM2.5 contributed by ships in Shanghai Port transported to inland region. Our results suggest that ship traffic has a non-negligible contribution on ambient levels of fine particles and secondary contribution of SO2 and NO2 emitted by ships need to be estimated on local and regional scale in future.► Air pollution including gas and aerosol in China's largest port was reported firstly. ► Heavy fuel oil samples were collected and analyzed for multiple elemental contents. ► Contributions of ship emission on PM2.5 in port and inland sites were estimated. ► More than 60% of ship emission could be transported to inland region.
Keywords: Shanghai Port; Aerosol; Air pollution; Shipping emission; V; Ni;

Personal, indoor and outdoor air pollution levels among pregnant women by Anna Schembari; Margarita Triguero-Mas; Audrey de Nazelle; Payam Dadvand; Martine Vrijheid; Marta Cirach; David Martinez; Francesc Figueras; Xavier Querol; Xavier Basagaña; Marloes Eeftens; Kees Meliefste; Mark J. Nieuwenhuijsen (287-295).
The aims of this study were to investigate the relationship between pregnant women's personal exposures to NO x , NO2, PM2.5 concentration and absorbance as a marker for black carbon and their indoor and outdoor concentration levels at their residence, and also to identify predictors of personal exposure and indoor levels using questionnaire and time activity data.We recruited 54 pregnant women in Barcelona who carried a personal PM2.5 sampler for two days and NO x /NO2 passive badges for one week, while indoor and outdoor PM2.5 and NO x /NO2 levels at their residence were simultaneously measured. Time activity and house characteristics were recorded. Gravimetry determinations for PM2.5 concentration and absorbance measurements were carried out on the PM2.5 filter samples.Levels of personal exposure to NO x , PM2.5 and absorbance were slightly higher than indoor and outdoor levels (geometric mean of personal NO x  = 61.9 vs indoor NO x  = 60.6 μg m−3), while for NO2 the indoor levels were slightly higher than the personal ones. Generally, there was a high statistically significant correlation between personal exposure and indoor levels (Spearman's r between 0.78 and 0.84). Women spent more than 60% of their time indoors at home. Ventilation of the house by opening the windows, the time spent cooking and indicators for traffic intensity were re-occurring statistically significant determinants of the personal and indoor pollutants levels with models for NO x explaining the 55% and 60% of the variability respectively, and models for NO2 explaining the 39% and 16% of the variability respectively. Models for PM2.5 and absorbance explained the least of the variability.Our findings improve the current understanding of the characterization and inter-associations between personal, indoor and outdoor pollution levels among pregnant women. Variability in personal and indoor NO x and to a lesser extent NO2 levels could be explained well, but not the variability in PM2.5 could be explained.► First study to report on the personal, indoor and outdoor black carbon levels of pregnant women. ► Time spent indoors by pregnant women does not differ much from that of general population. ► Variability in personal and indoor NO x and NO2 levels could be explained well, but not in PM2.5.
Keywords: Personal; Indoor; Outdoor; Traffic; Air pollution; Pregnancy;

Differential effects of fine and coarse particles on daily emergency cardiovascular hospitalizations in Hong Kong by Hong Qiu; Ignatius Tak-sun Yu; Xiaorong Wang; Linwei Tian; Lap Ah Tse; Tze Wai Wong (296-302).
Few studies have investigated the relationship of hospital admissions for cardiovascular diseases with fine (PM2.5: particles with an aerodynamic diameter less than 2.5 μm) and coarse particles (PMc: particles with an aerodynamic diameter between 2.5 and 10 μm) simultaneously. We aimed to estimate the differential effects of PM2.5 and PMc on emergency hospital admissions for cardiovascular diseases, after controlling for the gaseous pollutants. We conducted a time series analysis in Hong Kong using daily emergency hospital admissions for cardiovascular diseases, PM2.5 and PMc concentrations from January 2000 to December 2005. PMc concentrations were estimated by subtracting PM2.5 from PM10 measurements. Generalized additive Poisson models allowing overdispersion and autocorrelation were used to examine the effects of PM2.5 and PMc simultaneously, adjusting for time trends, weather conditions, influenza outbreaks, and gaseous pollutants. In two-pollutant model, an interquartile range (IQR) increase in the 2-day moving average (lag01) concentration of PM2.5 and PMc corresponded to 1.86% (95% CI: 0.85%, 2.88%) and −0.16% (95% CI: −1.07%, 0.76%) change of emergency hospital admissions for total circulatory diseases respectively. Results were sensitive to further inclusion of nitrogen dioxide but not of ozone and sulfur dioxide. We did not find any effects of PMc on circulatory hospitalizations independent of PM2.5. In conclusion, we confirmed the stronger and significant adverse effects of PM2.5, but no independent effect of PMc on emergency cardiovascular hospitalizations. The biological mechanisms underlying the differential effects of PM2.5 and PMc on cardiovascular diseases were discussed.Display Omitted► We examined the differential effects of fine and coarse particles on cardiovascular diseases. ► We confirmed the stronger adverse effects of fine particles. ► We found no independent effects of coarse particles. ► PM2.5 is more harmful, likely because it penetrates deeper into the lungs.
Keywords: Coarse particles; Cardiovascular diseases; Differential effect; Emergency hospital admissions; Fine particles; Time series study;

The spatial and seasonal variation of nitrogen dioxide and sulfur dioxide in Cape Breton Highlands National Park, Canada, and the association with lichen abundance by Mark D. Gibson; Mathew R. Heal; Zhengyan Li; James Kuchta; Gavin H. King; Alex Hayes; Sheldon Lambert (303-311).
Over 200,000 tourists per year visit Cape Breton Highlands National Park, Nova Scotia, Canada. The forests within the park are home to many rare epiphytic lichens, the species diversity of which has declined in some areas. The primary motivation for this study was to gain insight into the concentrations and potential local and long-range sources of air pollution, but its association with lichen species diversity was also examined. Ogawa passive diffusion samplers were used to measure nitrogen dioxide (NO2) and sulfur dioxide (SO2) in the park at 19 sites in the winter and 20 sites in the summer of 2011. An improvement in the sensitivity of the sampler analytical protocol was developed. The mean concentrations in the park of winter and summer NO2 (0.81 and 0.16 ppb) and SO2 (0.24 and 0.21 ppb) are not at levels known to be phytotoxic to lichen. The NO2 concentrations in winter were significantly (p = 0.001) higher than those in summer whilst the SO2 concentrations did not differ significantly between winter and summer (p = 0.429). Highest NO2 concentrations in both seasons were observed in the Grand Anse Valley, presumably due to the steep road, emissions from the Pleasant Bay community at the foot of the valley and the enclosed topography of this area reducing dispersion of primary emissions. The SO2 concentrations in the park tended to be greater at elevated sites than valley sites, consistent with dispersion from long-range, rather than local, sources for this pollutant. Significant predictors in a multilinear regression for an index of air purity (lichen based measure of air quality) were lichen species number (p = 0.009), forest old growth index (p = 0.001) and distance from roads (p < 0.001) (model R 2 = 0.8, model p = 0.004). The study suggests that local sources of pollution (roads emissions) are adversely associated with lichen species diversity in this National Park, compared with long-range transport, and that monitoring programs such as a lichen-based ‘index of air purity’ can reveal locations where ambient air pollution, although low, is nevertheless at a level that may cause ecological detriment. The implications from this work could be applicable to national parks elsewhere.► Spatiotemporal variation of NO2 and SO2 in a pristine Canadian National Park. ► SO2 associated with elevated sites within the Park. ► Significant spatial patterns observed for NO2 in the Park. ► Significant seasonal difference observed for NO2 but not for SO2. ► Significant predictors of the index of air purity were determined.
Keywords: Cape Breton Highlands National Park; Canada; NO2; SO2; Ogawa passive diffusion sampler; Lichen; Index of air purity;

Temporal stability of land use regression models for traffic-related air pollution by Rongrong Wang; Sarah B. Henderson; Hind Sbihi; Ryan W. Allen; Michael Brauer (312-319).
Land-use regression (LUR) is a cost-effective approach for predicting spatial variability in ambient air pollutant concentrations with high resolution. Models have been widely used in epidemiological studies and are often applied to time periods before or after the period of air quality monitoring used in model development. However, it is unclear how well such models perform when extrapolated over time.The objective of this study was to assess the temporal stability of LUR models over a period of 7 years in Metro Vancouver, Canada.A set of NO and NO2 LUR models based on 116 measurements were developed in 2003. In 2010, we made 116 measurements again, of which 73 were made at the exact same location as in 2003. We then developed 2010 models using updated data for the same predictor variables used in 2003, and also explored additional variables. Four methods were used to derive model predictions over 7 years, and predictions were compared with measurements to assess the temporal stability of LUR models.The correlation between 2003 NO and 2010 NO measurements was 0.87 with a mean (sd) decrease of 11.3 (9.9) ppb. For NO2, the correlation was 0.74, with a mean (sd) decrease of 2.4 (3.2) ppb. 2003 and 2010 LUR models explained similar amounts of spatial variation (R 2 = 0.59 and R 2 = 0.58 for NO; R 2 = 0.52 and R 2 = 0.63 for NO2, in 2003 and in 2010 respectively). The 2003 models explained more variability in the 2010 measurements (R 2 = 0.58–0.60 for NO; R 2 = 0.52–0.61 for NO2) than the 2010 models explained in the 2003 measurements (R 2 = 0.50–0.55 for NO; R 2 = 0.44–0.49 for NO2), and the 2003 models explained as much variability in the 2010 measurements as they did in the 2003 measurements.LUR models are able to provide reliable estimates over a period of 7 years in Metro Vancouver. When concentrations and their variability are decreasing over time, the predictive power of LUR models is likely to remain the same or to improve in forecasting scenarios, but to decrease in hind-casting scenarios.► Land use regression (LUR) models of traffic air pollution can be extended over time. ► LUR model application is improved for forecasting vs hind-casting scenarios. ► Epidemiologic studies can reliably apply LUR models over ∼7 year time periods.
Keywords: Land use regression (LUR); Temporal stability; Traffic-related air pollution; Exposure assessment; Vancouver;

In-vehicle particle air pollution and its mitigation by L. Tartakovsky; V. Baibikov; J. Czerwinski; M. Gutman; M. Kasper; D. Popescu; M. Veinblat; Y. Zvirin (320-328).
This work presents results of particle mass, number and size measurements inside passenger cars (PCs), vans and urban buses. Effects of the in-cabin air purifier on particle concentrations and average size inside a vehicle are studied. Use of the air purifier leads to a dramatic reduction, by 95–99%, in the measured ultrafine particles number concentration inside a vehicle compared with outside readings. Extremely low particle concentrations may be reached without a danger of vehicle occupants' exposure to elevated CO2 levels. The lowest values of particle concentrations inside a PC without air purifier are registered under the recirculation ventilation mode, but the issue of CO2 accumulation limits the use of this mode to very short driving events. Lower PM concentrations are found inside newer cars, if this ventilation mode is used. Great differences by a factor of 2.5–3 in PM10 concentrations are found between the PCs and the buses. Smoking inside a car leads to a dramatic increase, by approximately 90 times, in PM2.5 concentrations.► In-cabin air purifier provided reduction of particle number concentrations up to 99%. ► With in-cabin air purifier CO2 concentrations were kept below limits of the standard. ► Great differences in PM10 concentrations were found between the cars and the buses. ► Smoking inside a car leads to increase of PM2.5 concentrations by a factor of 90.
Keywords: Cabin air filtration; Vehicle occupants exposure; Particles; Ventilation mode; In-vehicle smoking;

Use of portable emissions measurement system (PEMS) for the development and validation of passenger car emission factors by Marina Kousoulidou; Georgios Fontaras; Leonidas Ntziachristos; Pierre Bonnel; Zissis Samaras; Panagiota Dilara (329-338).
This paper discusses the development and validation of passenger car emission factors, using real world operation data. In total, six passenger cars of different technologies were studied. The tested vehicles were operated under various driving conditions and over two different routes in the region of Lombardia, Italy. These routes were specifically defined in order to provide a range of driving conditions, including urban, rural and highway driving. Tailpipe emissions and exhaust gas flows were measured on-board the vehicle, using a portable emissions measurement system (PEMS). In addition, all vehicles were tested over the European type-approval driving cycle (NEDC) with the same PEMS equipment.The testing of gasoline vehicles showed that emissions are well below the emission standards and do not raise any concern. However, the testing of diesel vehicles both under real-world driving conditions and over the NEDC brought to the surface important concerns regarding the actual NO x emissions of modern diesel vehicles, since they seem to comply with the corresponding emission standard over the type-approval cycle, but they constantly exceed the specified limit when tested under real-world driving conditions. Results from real-world operation revealed that there is a significant deviation from the NO x emission standard limit (especially for the newly introduced Euro 5 technology). These observations raise concerns regarding the actual NO x emissions of modern vehicles and their impact on urban air-quality.The emission factors originally measured on the road are also compared to the corresponding COPERT average speed emission factors. In general, emissions of CO2, THC and CO correlate fairly well with COPERT, for all vehicles. In the case of NO x emissions, emission levels of the two tested Euro 5 diesel passenger cars are consistently higher in urban, rural, and highway driving compared to the corresponding COPERT emission factor. Thus, leading to the conclusion that more experimental data are necessary, especially for post-Euro 4 compliant diesel vehicles of different engine capacities particularly when it comes to NO x emissions from diesel vehicles.► Emissions from gasoline and diesel cars were studied using PEMS measurements. ► Important concerns raised about actual NO x emissions of modern diesel vehicles. ► For gasoline vehicles emissions remained below regulated limits. ► COPERT emission factor in most cases reflect adequately real world performance. ► Need for additional data input in COPERT particularly for Euro 5 cars.
Keywords: Emission factors; Regulated pollutants; PEMS; Real world emissions; Passenger cars; COPERT;

VOC emissions of smouldering combustion from Mediterranean wildfires in central Portugal by Margarita Evtyugina; Ana Isabel Calvo; Teresa Nunes; Célia Alves; Ana Patrícia Fernandes; Luís Tarelho; Ana Vicente; Casimiro Pio (339-348).
Emissions of trace gases and C5–C10 volatile organic compounds (VOCs) from Mediterranean wildfires occurring in Portugal in summer 2010 were studied. Fire smoke was collected in Tedlar bags and analysed for CO, CO2, total hydrocarbons (THC) and VOCs. The CO, CO2 and THC emission factors (EFs) were 206 ± 79, 1377 ± 142 and 8.1 ± 9 g kg−1 biomass burned (dry basis), respectively. VOC emissions from Mediterranean wildfires were reported for the first time. Aromatic hydrocarbons were major components of the identified VOC emissions. Among them, benzene and toluene were dominant compounds with EFs averaging 0.747 ± 0.303 and 0.567 ± 0.422 g kg−1 biomass burned (dry basis), respectively. Considerable amounts of oxygenated organic volatile compounds (OVOCs) and isoprenoids were detected. 2-Furaldehyde and hexanal were the most abundant measured OVOCs with EFs of 0.337 ± 0.259 and 0.088 ± 0.039 g kg−1 biomass burned (dry basis), respectively. The isoprenoid emissions were dominated by isoprene (EF = 0.207 ± 0.195 g kg−1 dry biomass burned) and α-pinene (EF = 0.112 ± 0.093 g kg−1 dry biomass burned). Emission data obtained in this work are useful for validating and improving emission inventories, as well for carrying out modelling studies to assess the effects of vegetation fires on air pollution and tropospheric chemistry.► The CO, CO2, THC and VOC emissions from Mediterranean wildfires were studied. ► The CO and CO2 emissions comprised 78 ± 8% and 18 ± 7% of the total carbon emitted. ► Aromatic hydrocarbons were major components (∼51%) of the identified VOC emissions. ► Benzene and toluene were dominant aromatic compounds. ► Isoprenoid emissions were dominated by isoprene and α-pinene.
Keywords: Wildfires; Mediterranean forest; Emission factors; Trace gases; VOCs;

Modelling secondary organic aerosol in the United Kingdom by A.L. Redington; R.G. Derwent (349-357).
The Lagrangian atmospheric dispersion model, NAME, has been used to model the formation and transport of anthropogenic and biogenic secondary organic aerosol (SOA) over North-West Europe in 2008. The model has been tested against daily organic carbon measurements at Harwell, a rural site in southern UK, where it was able to represent adequately the observed values in summer, with some under-prediction in winter. The model has been used to look at the contribution of SOA to total measured PM10 at four selected UK sites. The site with the greatest contribution (32%) of SOA to PM10 was Auchencorth, a rural site in Scotland and least (9%) at London Bloomsbury. The biogenic SOA (BSOA) dominated over the anthropogenic SOA (ASOA) in the UK and showed a strong seasonal cycle peaking in the summer. There was also a slight summer increase in ASOA. The model has been employed to provide source attribution between UK sources and sources in the rest of Europe. The contribution from Europe was generally small but varied considerably due to meteorology. The UK component showed a seasonal cycle, peaking in the summer months. On an annual basis, considering the four measurement sites, the percentage of SOA arriving from outside the UK was least at Auchencorth (9.8%) and most at London (28.4%). Total modelled SOA had a maximum contribution of 2–3 μg m−3 as a monthly average. (It should be noted that in addition there will be a small contribution from background SOA to these figures.) Emission sensitivity studies revealed that the response of ASOA was highly non-linear, showing both positive and negative responses to a 30% reduction in all man-made NOx sources and the response was greater than 1:1 to a 30% reduction in all man-made VOC sources. BSOA showed only a small negative response to a 30% NOx reduction and no change to a 30% VOC reduction.► Modelled anthropogenic and biogenic secondary organic aerosol (SOA) are presented. ► Comparison with measured organic carbon data at a rural UK site. ► Biogenic SOA dominates over anthropogenic SOA in the UK. ► On an annual basis, 30% of modelled SOA in London originates from outside the UK. ► Total modelled SOA had a maximum contribution of 2–3 μg m−3 as a monthly average.
Keywords: Organic carbon; PM10; Secondary organic aerosol;

Influence of Southeast Asian biomass burning on ozone and carbon monoxide over subtropical Taiwan by Yu Chi Lin; Chuan Yao Lin; Po Hsiung Lin; Guenter Engling; Yen Ching Lin; Yung Yao Lan; Chiung Wen June Chang; Tien Ho Kuo; Wei Ting Hsu; Chia Chun Ting (358-365).
Surface ozone (O3) and carbon monoxide (CO) mixing ratios were measured at Mei-Feng (24.05 °N, 120.10 °E, 2269 m above sea level) remote mountain site between March 2009 and September 2010 to investigate the impact of regional pollution on O3 and CO. The results showed that the maximum values of both O3 and CO were found in the springtime. Backward trajectory analysis, combined with MODIS fire spots suggested that the enhanced O3 and CO in springtime could be attributed to biomass burning (BB) activities over Southeast (SE) Asia. Thirteen BB events were identified by backward trajectory analysis, MODIS fires, NCEP weather data sets and CO concentrations. Good correlation between O3 and CO was found during the BB plumes. Using the linear regression, the slope (ΔO3/ΔCO) was calculated to be 0.18 ± 0.08 (mean ± 1σ). This value was in agreement with that of 0.2 observed over the west Pacific region during the TRACE-P campaign, but was higher than those (0.11–0.14) of Canadian and Siberian fires. Moreover, significant enhanced O3 productivity was also found in aged BB plumes and that mixed with urban emissions from SE coastal China. To assess the net influence of SE Asian BB, the air masses from SE Asia and SE China were divided in two groups: those that passed over the fire regions (PF) and those that did not (NP). The result showed that the maximum differences between PF and NP were estimated in March with 8 ppb for O3 and 45 ppb for CO, respectively, accounting for 23% of both CO and O3 levels at Mei-Feng. Although uncertainties existed in the estimations, the significant discrepancies of O3 and CO in the two air groups suggested the air pollutants emitted by SE Asian BB could be transported and influence the air quality over subtropical Taiwan in springtime.► We examine the spring-maximum of O3 and CO levels in subtropical Taiwan are attributed to Southeast Asian biomass burning. ► The average ΔO3/ΔCO ratio in fire plumes is 0.18 ± 0.08. ► Enhanced O3 production in aged fire plume and that mixed with urban emissions is found. ► The net influence of Southeast Asian biomass burning on both tropospheric O3 and CO was approximately 23% in March.
Keywords: Ozone; Carbon monoxide; Biomass combustion; Long-range transport; Asian outflow; ΔO3/ΔCO ratio;

Seasonal variation in the spatial distribution of aerosol black carbon over Bay of Bengal: A synthesis of multi-campaign measurements by Sobhan Kumar Kompalli; S. Suresh Babu; K. Krishna Moorthy; Vijayakumar S. Nair; Mukunda M. Gogoi; Jai Prakash Chaubey (366-373).
Synthesizing data from several cruise experiments over the Bay of Bengal (BoB), the seasonal characterization of aerosol black carbon (BC) mass concentration was made. The study indicated that the BC mass concentration (M BC) showed significant seasonal variation over the oceanic region with M BC being the highest during the winter season (∼2407 ± 1756 ng m−3) and lowest in summer monsoon (∼765 ± 235 ng m−3). The seasonal changes in the BC mass concentration were more prominent over the northern BoB (having an annual amplitude of ∼4) compared to southern BoB (amplitude ∼ 2). Significant spatial gradients in M BC, latitudinal as well as longitudinal, existed in all the seasons. Latitudinal gradients, despite being consistently increasing northwards, were found to be sharper during winter and weakest during summer monsoon with e-fold scaling distances of ∼7.7° and ∼15.6° during winter and summer monsoon seasons respectively. Longitudinally, BC concentrations tend to increase toward east during winter and premonsoon seasons, but an opposite trend was seen in monsoon season highlighting the seasonally changing source impacts on BC loading over BoB. Examination of the results in light of possible role of transport from adjoining landmasses, using airmass back trajectory cluster analysis, also supported spatially and temporally varying source influence on oceanic region.► A synthesis of the black carbon (BC) data from multi-campaign measurements over Bay of Bengal was made. ► BC showed significant seasonal variation in its spatial distribution over Bay of Bengal. ► Advection and long-range transport played a crucial role in modulating the spatial distribution of BC over BoB.
Keywords: Black carbon; Bay of Bengal; Spatial gradients;

Equations are developed for the expected changes in the equilibrium levels of organic particulate matter (OPM) and aerosol water as may be caused by changes in a range of system parameters that includes temperature T, the governing gas/particle partitioning coefficients, the mean molecular weight of the absorbing PM phase MW ¯ (g mol−1), the total gas + particle concentrations of one or more of the condensable organic species, and the gaseous water concentration. These equations will be useful when considering how PM levels may respond to changing system parameters. The equations are developed for organic + water systems assuming equilibrium gas/particle partitioning theory as developed previously [Pankow, J.F., 1994. An absorption model of gas/particle partitioning of organic compounds in the atmosphere. Atmospheric Environment 28, 185–188].
Keywords: Organic particulate matter, OPM; Secondary organic aerosol, SOA; Absorption model; Sensitivity analysis; Temperature effects; RH effects;