Atmospheric Environment (v.163, #C)

Influence of Saharan dust outbreaks and carbon content on oxidative potential of water-soluble fractions of PM2.5 and PM10 by Daniela Chirizzi; Daniela Cesari; Maria Rachele Guascito; Adelaide Dinoi; Livia Giotta; Antonio Donateo; Daniele Contini (1-8).
Exposure to atmospheric particulate matter (PM) leads to adverse health effects although the exact mechanisms of toxicity are still poorly understood. Several studies suggested that a large number of PM health effects could be due to the oxidative potential (OP) of ambient particles leading to high concentrations of reactive oxygen species (ROS). The contribution to OP of specific anthropogenic sources like road traffic, biomass burning, and industrial emissions has been investigated in several sites. However, information about the OP of natural sources are scarce and no data is available regarding the OP during Saharan dust outbreaks (SDO) in Mediterranean regions. This work uses the a-cellular DTT (dithiothreitol) assay to evaluate OP of the water-soluble fraction of PM2.5 and PM10 collected at an urban background site in Southern Italy. OP values in three groups of samples were compared: standard characterised by concentrations similar to the yearly averages; high carbon samples associated to combustion sources (mainly road traffic and biomass burning) and SDO events. DTT activity normalised by sampled air volume (DTTV), representative of personal exposure, and normalised by collected aerosol mass (DTTM), representing source-specific characteristics, were investigated. The DTTV is larger for high PM concentrations. DTTV is well correlated with secondary organic carbon concentration. An increased DTTV response was found for PM2.5 compared to the coarse fraction PM2.5-10. DTTV is larger for high carbon content samples but during SDO events is statistically comparable with that of standard samples. DTTM is larger for PM2.5 compared to PM10 and the relative difference between the two size fractions is maximised during SDO events. This indicates that Saharan dust advection is a natural source of particles having a lower specific OP with respect to the other sources acting on the area (for water-soluble fraction). OP should be taken into account in epidemiological studies to evaluate the potential health risks associated to ROS in regions affected by high pollution events due to Saharan dust advection.Display Omitted
Keywords: Oxidative potential; DTT assay; PM2.5; PM10; Saharan dust;

Black carbon emissions in Russia: A critical review by Meredydd Evans; Nazar Kholod; Teresa Kuklinski; Artur Denysenko; Steven J. Smith; Aaron Staniszewski; Wei Min Hao; Liang Liu; Tami C. Bond (9-21).
This study presents a comprehensive review of estimated black carbon (BC) emissions in Russia from a range of studies. Russia has an important role regarding BC emissions given the extent of its territory above the Arctic Circle, where BC emissions have a particularly pronounced effect on the climate. We assess underlying methodologies and data sources for each major emissions source based on their level of detail, accuracy and extent to which they represent current conditions. We then present reference values for each major emissions source. In the case of flaring, the study presents new estimates drawing on data on Russia's associated petroleum gas and the most recent satellite data on flaring. We also present estimates of organic carbon (OC) for each source, either based on the reference studies or from our own calculations. In addition, the study provides uncertainty estimates for each source. Total BC emissions are estimated at 688 Gg in 2014, with an uncertainty range 401 Gg-1453 Gg, while OC emissions are 9224 Gg with uncertainty ranging between 5596 Gg and 14,736 Gg. Wildfires dominated and contributed about 83% of the total BC emissions: however, the effect on radiative forcing is mitigated in part by OC emissions. We also present an adjusted estimate of Arctic forcing from Russia's BC and OC emissions. In recent years, Russia has pursued policies to reduce flaring and limit particulate emissions from on-road transport, both of which appear to significantly contribute to the lower emissions and forcing values found in this study.
Keywords: Black carbon; Organic carbon; Russia; Emission inventory; Radiative forcing;

Simultaneous measurements of meteorological data, trace gases, and volatile organic compounds were made in two regional sites, viz. Backgarden and Kaiping, in the Pearl River Delta (PRD) during summer and autumn, respectively. The strong deviations from the NO-NO2-O3 Photostationary State, quantified by the leighton ratios, are carefully deduced through a comprehensive data set consist of the high-quality measurements of NO, NO2, O3 and J NO2 as well as the peroxy radical measurements. This is the first report of the Leighton ratio in China, with relatively high recorded values of 2.3 ± 0.4 (Backgarden) and 3.1 ± 1.4 (Kaiping), suggesting a strongly oxidising atmosphere in the PRD, typical of the ozone pollution season. A sensitivity analysis using a zero-dimensional chemical box model based on the regional atmospheric chemistry mechanism, version 2 (RACM2) constrained by the experimental measurements, indicated that peroxy radicals account for 70 (Backgarden) and 66% (Kaiping) of the observed positive deviations from the NO x photostationary state (characterized by a Leighton ratio of 1) on average. We consider that the remaining deviations result from neglecting the effects of chlorine chemistry, so we introduced a Cl chemistry module into RACM2, and the modelled results for Cl were as follows: 4.7 × 10−4 pptv in Backgarden and 1.3 × 10−3 pptv in Kaiping; these results are lower than the Cl concentration derived from the NO x photostationary state. More work is required to confirm the role of additional peroxy radical sources at both high and low NO x regimes, as well as that of the halogen radicals, in perturbing the NO-NO x -O3 cycle, which would significantly enhance trace gas removal and photochemical ozone production.
Keywords: Leighton ratio; Pearl River Delta; RACM2; Chlorine chemistry; Peroxy radical;

In recent years, haze pollution and high concentrations of particulate matter frequently occur in many mega cities of China, which has seriously impacted the regional air quality, and further caused harm to human health. Although satellite observation provides a convenient way to evaluate air quality in space and time, satellite measurements do not separate between natural and anthropogenic aerosols. To discriminate anthropogenic aerosol contribution from satellite observations, we proposed the concept of Local Aerosol Optical Depth (LAOD) to describe the localized aerosol loading. A comparative analysis was performed between seasonal/monthly Mean AOD (MAOD), LAOD and ground measured PM2.5/PM10. The comparison results show that LAOD has better linear relationship with PM2.5/PM10 than MAOD in central and eastern China with persistent localized aerosol emissions. Based on the MODIS Deep Blue AOD dataset from 2001 to 2015, we analyzed the spatio-temporal distribution of LAOD over China. Spatially, high LAODs are mainly distributed in Sichuan basin, North China Plain, and central China; temporally, LAOD over China presents an upward trend (+0.003 year−1) during 2001–2007 and a weak downward (−0.002 year−1) trend from 2008 to 2015. LAOD was also found to be highly correlated with haze frequency over most areas of central and eastern China, especially in North China Plain with a correlation coefficient of 0.87 (P < 0.01). It demonstrates the significant impact of local anthropogenic aerosol emission on regional haze pollution in China.
Keywords: Aerosol optical depth; MODIS; Anthropogenic aerosol; Haze pollution;

Estimation of atmospheric aging time of black carbon particles in the polluted atmosphere over central-eastern China using microphysical process analysis in regional chemical transport model by Xueshun Chen; Zifa Wang; Fangqun Yu; Xiaole Pan; Jie Li; Baozhu Ge; Zhe Wang; Min Hu; Wenyi Yang; Huansheng Chen (44-56).
Mixing state of black carbon (BC) particles has significant impacts on their radiative forcing, visibility impairment and the ability in modifying cloud formation. In this study, an aging scheme of BC particles using prognostic variables based on aerosol microphysics was incorporated into a regional atmospheric chemistry model, Nested Air Quality Prediction Modeling System with Advanced Particle Microphysics (NAQPMS + APM), to investigate the temporal and spatial variations in aging time scale of BC particles in polluted atmosphere over central-eastern China. The model results show that the aging time scale has a clear diurnal variation with a lower value in the daytime and a higher value in the nighttime. The shorter aging time scale in the daytime is due to condensation aging associated with intense photochemical reaction while the longer aging time scale in the nighttime is due to coagulation aging, which is much slower than that due to condensation. In Beijing, the aging time scale is 2 h or less in the surface layer in daytime, which is far below the fixed 1.2 days used in many models. As a result, the fraction of hydrophilic BC particles by the new scheme is larger than that by the scheme with fixed aging time scale though the mean aging time scale by the new scheme is much larger than 1.2 days. Hydrophilic fraction of BC particles increases with the increase of height. Over central-eastern China, the averaged aging time scale calculated by the new scheme is in the range from 12 h to 7 days, with higher values in regions far from the source areas. Hydrophilic fraction of BC particles is more than 90% at the higher levels in polluted atmosphere. Difference of simulated BC concentration with internal mixing and microphysical aging is within 5%, indicating that the assumption of internal mixing for BC particles to respond to in-cloud scavenging is more appropriate than the external mixing assumption in polluted atmosphere over central-eastern China.
Keywords: Black carbon(BC); Microphysics; Aging; NAQPMS+APM;

From November 2012 to July 2013, a sampling campaign was completed for comprehensive characterization of PM2.5 over four key emission regions in China: Beijing-Tianjin-Hebei (BTH), Yangzi River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SB). A multi-method approach, adopting different analytical and receptor modeling methods, was employed to determine the relative abundances of region-specific air pollution constituents and contributions of emission sources. This paper is focused on organic molecular marker based source apportionment using chemical mass balance (CMB) receptor modeling. Analyses of the organic molecular markers revealed that vehicle emission, coal combustion, biomass burning, meat cooking and natural gas combustion were the major contributors to organic carbon (OC) in PM2.5. The vehicle emission dominated the sources contributing to OC in spring at four sampling sites. During wintertime, the coal combustion had highest contribution to OC at BTH site, while the major source contributing to OC at YRD and PRD sites was vehicle emission. In addition, the relative contributions of different emission sources to PM2.5 mass at a specific location site and in a specific season revealed seasonal and spatial variations across all four sampling locations. The largest contributor to PM2.5 mass was secondary sulfate (14–17%) in winter at the four sites. The vehicle emission was found to be the major source (14–21%) for PM2.5 mass at PRD site. The secondary ammonium has minor variation (4–5%) across the sites, confirming the influences of regional emission sources on these sites. The distinct patterns of seasonal and spatial variations of source apportionment observed in this study were consistent with the findings in our previous paper based upon water-soluble ions and carbonaceous fractions. This makes it essential for the local government to make season- and region-specific mitigation strategies for abating PM2.5 pollution in China.
Keywords: PM2.5; Organic aerosol; Source apportionment; Receptor model;

Atmospheric ammonia (NH3) is not only a major precursor gas for fine particulate matter (PM2.5), but it also negatively impacts the environment through eutrophication and acidification. As the need for agriculture, the largest contributing source of NH3, increases, NH3 emissions will also increase. Therefore, it is crucial to accurately predict ammonia concentrations. The objective of this study is to determine how well the U.S. National Oceanic and Atmospheric Administration (NOAA) National Air Quality Forecast Capability (NAQFC) system predicts ammonia concentrations using their Community Multiscale Air Quality (CMAQ) model (v4.6). Model predictions of atmospheric ammonia are compared against measurements taken during the NOAA California Nexus (CalNex) field campaign that took place between May and July of 2010. Additionally, the model predictions were also compared against ammonia measurements obtained from the Tropospheric Emission Spectrometer (TES) on the Aura satellite. The results of this study showed that the CMAQ model tended to under predict concentrations of NH3. When comparing the CMAQ model with the CalNex measurements, the model under predicted NH3 by a factor of 2.4 (NMB = −58%). However, the ratio of the median measured NH3 concentration to the median of the modeled NH3 concentration was 0.8. When compared with the TES measurements, the model under predicted concentrations of NH3 by a factor of 4.5 (NMB = −77%), with a ratio of the median retrieved NH3 concentration to the median of the modeled NH3 concentration of 3.1. Because the model was the least accurate over agricultural regions, it is likely that the major source of error lies within the agricultural emissions in the National Emissions Inventory. In addition to this, the lack of the use of bidirectional exchange of NH3 in the model could also contribute to the observed bias.

Ship exhaust emissions need to be allocated accurately in both space and time in order to examine many of the associated impacts, including on air quality and health. Data on ship activity from the Automatic Identification System (AIS) allow ship exhaust emissions to be calculated with fine spatial and temporal resolution. However, there are spatial gaps in the coverage afforded by the coastal network of ground stations that are used to collect the AIS data. This paper focuses on the problem of allocating emissions to the coastal gap regions. Allocating emissions to these regions involves generating interpolated ship tracks that both span the gaps and avoid coming too close to land. In most cases, a simple shortest path or straight line interpolation produces tracks that do not overlap or come too close to land. Where the simple method does not produce acceptable results, vessel tracks are steered around land on shortest available paths using a combination of visibility graphs and Dijkstra's algorithm. A geographical cluster analysis is first used to identify the boundary regions of the data gaps. The properties of the data gaps are summarised in terms of the length, duration and speed of the spanning tracks. The interpolation methods are used to improve the spatial distribution of emissions. It is also shown that emissions in the gap regions can contribute substantially to the total ship exhaust emissions in close proximity to highly populated areas.
Keywords: Ship exhaust emissions; AIS activity data; Extensive coastal regions; Data gaps; Emissions mapping; Regional inventory;

Formulation of the Lagrangian particle model LAPMOD and its evaluation against Kincaid SF6 and SO2 datasets by Roberto Bellasio; Roberto Bianconi; Sonia Mosca; Paolo Zannetti (87-98).
This paper presents the Lagrangian particle model LAPMOD for modeling time-variable emissions in atmosphere of inert and radioactive gases and aerosols. LAPMOD is fully interfaced with the meteorological model CALMET (Scire et al., 1999a), part of the US-EPA recommended CALPUFF modeling system (EPA, 2017), and can also use the meteorological input files produced with the AERMET meteorological processor of US-EPA recommended model AERMOD (EPA, 2004).The paper outlines the theory on which LAPMOD is based and provides the results of the evaluation of LAPMOD against the Kincaid SF6 and SO2 classical field studies and tracer experiments. The performance of LAPMOD is successfully evaluated with the Model Evaluation Kit (Olesen, 2005) and compared with that of other air quality models.
Keywords: Lagrangian particle model; Kernel smoother; Model evaluation; Kincaid;

Sample integrity evaluation and EPA method 325B interlaboratory comparison for select volatile organic compounds collected diffusively on Carbopack X sorbent tubes by Karen D. Oliver; Tamira A. Cousett; Donald A. Whitaker; Luther A. Smith; Shaibal Mukerjee; Casson Stallings; Eben D. Thoma; Lillian Alston; Maribel Colon; Tai Wu; Stacy Henkle (99-106).
A sample integrity evaluation and an interlaboratory comparison were conducted in application of U.S. Environmental Protection Agency (EPA) Methods 325A and 325B for diffusively monitoring benzene and other selected volatile organic compounds (VOCs) using Carbopack X sorbent tubes. To evaluate sample integrity, VOC samples were refrigerated for up to 240 days and analyzed using thermal desorption/gas chromatography-mass spectrometry at the EPA Office of Research and Development laboratory in Research Triangle Park, NC, USA. For the interlaboratory comparison, three commercial analytical laboratories were asked to follow Method 325B when analyzing samples of VOCs that were collected in field and laboratory settings for EPA studies. Overall results indicate that the selected VOCs collected diffusively on sorbent tubes generally were stable for 6 months or longer when samples were refrigerated. This suggests the specified maximum 30-day storage time of VOCs collected diffusively on Carbopack X passive samplers and analyzed using Method 325B might be able to be relaxed. Interlaboratory comparison results were in agreement for the challenge samples collected diffusively in an exposure chamber in the laboratory, with most measurements within ±25% of the theoretical concentration. Statistically significant differences among laboratories for ambient challenge samples were small, less than 1 part per billion by volume (ppbv). Results from all laboratories exhibited good precision and generally agreed well with each other.
Keywords: EPA Method 325; Benzene; 1,3-Butadiene; Refinery fenceline rule; Sample integrity evaluation; Carbopack X sorbent tubes;

Haze pollution in China, dominated by the aerosol particulate matters smaller than 2.5 μm (PM2.5) has raised much concern over the past decade. PM2.5 is principally derived from secondary new particulate formation (NPF) with main precursors SO2, NO2, NH3 and organic compounds (OC), where NH3 is the only alkaline inorganic gas. However, due to the lack understanding of NH3's role in NPF, few attention has been paid to NH3, which hinders the haze mitigation in China. In this work, the role of NH3 in NPF is investigated theoretically with a new kinetic model. Combining the oxidation of SO2/NO2 in SO2/NO2/NH3/H2O/air system and the aggregation of clusters in H2SO4/HNO3/NH3/OC system, this model has been established based on gas-kinetic theory, and tested upon uncertainty analysis with Monte Carlo method. The results of NPF calculations at the atmospheric concentration of each precursor show that NH3 is able to enhance NPF indirectly by facilitating conversions of SO2 and NO2, and directly by promoting aggregations of H2SO4, HNO3, NH3 and OC. The major effect of NH3 on NPF is found to be the enhancement of conversion fractions for SO2 and NO2 during oxidation processes. In addition, the promotion in contribution of HNO3 to NPF due to NH3 has been particularly observed. Therefore, controlling the emission of NH3 strictly as current restrictions on SO2 and NOx is reasonable to mitigating the haze pollution in China which has much higher atmospheric NH3 concentration over the global average level.Display Omitted
Keywords: NH3; New particle formation; PM2.5; Haze mitigation;

Chemical characterization and oxidative potential of particles emitted from open burning of cereal straws and rice husk under flaming and smoldering conditions by Akihiro Fushimi; Katsumi Saitoh; Kentaro Hayashi; Keisuke Ono; Yuji Fujitani; Ana M. Villalobos; Brandon R. Shelton; Akinori Takami; Kiyoshi Tanabe; James J. Schauer (118-127).
Open burning of crop residue is a major source of atmospheric fine particle emissions. We burned crop residues (rice straws, barley straws, wheat straws, and rice husks produced in Japan) in an outdoor chamber and measured particle mass, composition (elemental carbon: EC, organic carbon: OC, ions, elements, and organic species), and oxidative potential in the exhausts. The fine particulate emission factors from the literature were within the range of our values for rice straws but were 1.4–1.9 and 0.34–0.44 times higher than our measured values for barley straw and wheat straw, respectively. For rice husks and wheat straws, which typically lead to combustion conditions that are relatively mild, the EC content of the particles was less than 5%. Levoglucosan seems more suitable as a biomass burning marker than K+, since levoglucosan/OC ratios were more stable than K+/particulate mass ratios among crop species. Stigmasterol and β-sitosterol could also be used as markers of biomass burning with levoglucosan or instead of levoglucosan. Correlation analysis between chemical composition and combustion condition suggests that hot or flaming combustions enhance EC, K+, Cl and polycyclic aromatic hydrocarbons emissions, while low-temperature or smoldering combustions enhance levoglucosan and water-soluble organic carbon emissions. Oxidative potential, measured with macrophage-based reactive oxygen species (ROS) assay and dithiothreitol (DTT) assay, of open burning fine particles per particulate mass as well as fine particulate emission factors were the highest for wheat straws and second highest for rice husks and rice straws. Oxidative potential per particulate mass was in the lower range of vehicle exhaust and atmosphere. These results suggest that the contribution of open burning is relatively small to the oxidative potential of atmospheric particles. In addition, oxidative potential (both ROS and DTT activities) correlated well with water-insoluble organic species, suggesting that OC components, especially water-insoluble OC components emitted under non-flaming combustion, have a major impact on oxidative potential.Display Omitted
Keywords: Biomass burning; Levoglucosan; Redox activity; Reactive oxygen species; Dithiothreitol; Source profile;

The Photochemical Ozone Creation Potential (POCP) scale quantifies the relative abilities of volatile organic compounds (VOCs) to produce ground level ozone. POCP values are usually calculated using atmospheric boundary layer models containing detailed representations of atmospheric VOC degradation chemistry. The sensitivity of POCP values to variation of a number of kinetic and mechanistic parameters has been investigated here. It is shown that POCP values for VOCs can be rationalized in terms of their molecular structure and OH reactivity. As a result, a simple method has been developed and optimized that allows POCP values for north-west European and USA urban reference conditions to be estimated for alkanes, alkenes, aromatic hydrocarbons, and several oxygenated VOC classes without the requirement to construct a detailed chemical mechanism or run an atmospheric model. The procedure for determining the estimated POCP value (POCPE) is described, and the results are presented and discussed.
Keywords: VOC oxidation; Tropospheric chemistry; POCP; Ozone formation potential; Secondary pollutants; Impact assessment;

Cytotoxic and genotoxic responses of human lung cells to combustion smoke particles of Miscanthus straw, softwood and beech wood chips by Ali Talib Arif; Christoph Maschowski; Patxi Garra; Manuel Garcia-Käufer; Tatiana Petithory; Gwenaëlle Trouvé; Alain Dieterlen; Volker Mersch-Sundermann; Polla Khanaqa; Irina Nazarenko; Richard Gminski; Reto Gieré (138-154).
Inhalation of particulate matter (PM) from residential biomass combustion is epidemiologically associated with cardiovascular and pulmonary diseases. This study investigates PM0.4-1 emissions from combustion of commercial Miscanthus straw (MS), softwood chips (SWC) and beech wood chips (BWC) in a domestic-scale boiler (40 kW). The PM0.4-1 emitted during combustion of the MS, SWC and BWC were characterized by ICP-MS/OES, XRD, SEM, TEM, and DLS. Cytotoxicity and genotoxicity in human alveolar epithelial A549 and human bronchial epithelial BEAS-2B cells were assessed by the WST-1 assay and the DNA-Alkaline Unwinding Assay (DAUA). PM0.4-1 uptake/translocation in cells was investigated with a new method developed using a confocal reflection microscope.SWC and BWC had a inherently higher residual water content than MS. The PM0.4-1 emitted during combustion of SWC and BWC exhibited higher levels of Polycyclic Aromatic Hydrocarbons (PAHs), a greater variety of mineral species and a higher heavy metal content than PM0.4-1 from MS combustion. Exposure to PM0.4-1 from combustion of SWC and BWC induced cytotoxic and genotoxic effects in human alveolar and bronchial cells, whereby the strongest effect was observed for BWC and was comparable to that caused by diesel PM (SRM 2 975), In contrast, PM0.4-1 from MS combustion did not induce cellular responses in the studied lung cells. A high PAH content in PM emissions seems to be a reliable chemical marker of both combustion efficiency and particle toxicity. Residual biomass water content strongly affects particulate emissions and their toxic potential. Therefore, to minimize the harmful effects of fine PM on health, improvement of combustion efficiency (aiming to reduce the presence of incomplete combustion products bound to PM) and application of fly ash capture technology, as well as use of novel biomass fuels like Miscanthus straw is recommended.Display Omitted
Keywords: Biomass combustion; Miscanthus straw; Wood chips; PM0.4-1 emissions; Polycyclic aromatic hydrocarbons (PAHs); Toxicity;

Modelling NOX concentrations through CFD-RANS in an urban hot-spot using high resolution traffic emissions and meteorology from a mesoscale model by Beatriz Sanchez; Jose Luis Santiago; Alberto Martilli; Fernando Martin; Rafael Borge; Christina Quaassdorff; David de la Paz (155-165).
Air quality management requires more detailed studies about air pollution at urban and local scale over long periods of time. This work focuses on obtaining the spatial distribution of NO x concentration averaged over several days in a heavily trafficked urban area in Madrid (Spain) using a computational fluid dynamics (CFD) model. A methodology based on weighted average of CFD simulations is applied computing the time evolution of NO x dispersion as a sequence of steady-state scenarios taking into account the actual atmospheric conditions. The inputs of emissions are estimated from the traffic emission model and the meteorological information used is derived from a mesoscale model. Finally, the computed concentration map correlates well with 72 passive samplers deployed in the research area. This work reveals the potential of using urban mesoscale simulations together with detailed traffic emissions so as to provide accurate maps of pollutant concentration at microscale using CFD simulations.Display Omitted
Keywords: CFD Model; Urban air quality; Traffic emission model; Mesoscale model; Passive samplers;

This study provides observational results of aerosol optical and radiative characteristics over four locations in IGP. Spectral variation of Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA) and Asymmetry Parameter (AP) were analysed using AErosol RObotic NETwork (AERONET) data. The analysis revealed that coarse particles were dominant in summer and pre-monsoon, while fine particles were more pronounced in winter and post-monsoon. Furthermore, the spatio-temporal variations of Shortwave Direct Aerosol Radiative Forcing (SDARF) and Shortwave Direct Aerosol Radiative Forcing Efficiency (SDARFE) at the Top Of Atmosphere (TOA), SURface (SUR) and within ATMosphere (ATM) were calculated using SBDART model. The atmospheric Heating Rate (HR) associated with SDARFATM were also computed. It was observed that the monthly averaged SDARFTOA and SDARFSUR were found to be negative leading to positive SDARFATM during all the months over all sites. The increments in net atmospheric forcing lead to maximum HR in November–December and May. The seasonal analysis of SDARF revealed that SDARFTOA and SDARFSUR were negative during all seasons. The SW atmospheric absorption translates to highest atmospheric HR during summer over Karachi and during pre-monsoon over Lahore, Jaipur and Kanpur. Like SDARF, the monthly and seasonal variations of SDARFETOA and SDARFESUR were found to be negative, resulting in positive atmospheric forcing. Additionally, to compare the model estimated forcing against AERONET derived forcing, the regression analysis of AERONET-SBDART forcing were carried out. It was observed that SDARF at SUR and TOA showed relatively higher correlation over Lahore, moderate over Jaipur and Kanpur and lower over Karachi. Finally, the analysis of National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model revealed that air masses were arriving from multiple source locations.
Keywords: aerosol radiative forcing; Aerosol radiative forcing efficiency; Heating rate; Indo-Gangetic plains;

Microbial ice nucleators scavenged from the atmosphere during simulated rain events by Regina Hanlon; Craig Powers; Kevin Failor; Caroline L. Monteil; Boris A. Vinatzer; David G. Schmale (182-189).
Rain and snow collected at ground level have been found to contain biological ice nucleators. These ice nucleators have been proposed to have originated in clouds, where they may have participated in the formation of precipitation via ice phase nucleation. We conducted a series of field experiments to test the hypothesis that at least some of the microbial ice nucleators (prokaryotes and eukaryotes) present in rain may not originate in clouds but instead be scavenged from the lower atmosphere by rainfall. Thirty-three simulated rain events were conducted over four months off the side of the Smart Road Bridge in Blacksburg, VA, USA. In each event, sterile water was dispensed over the side of the bridge and recovered in sterile containers in an open fallow agricultural field below (a distance of ∼55 m). Microbes scavenged from the simulated rain events were cultured and their ice nucleation activity was examined. Putative microbial ice nucleators were cultured from 94% (31/33) of the simulated rain events, and represented 1.5% (121/8331) of the total colonies assayed. Putative ice nucleators were subjected to additional droplet freezing assays, and those confirmed through these repeated assays represented 0.4% (34/8331) of the total. Mean CFUs scavenged by simulated rain ranged from 2 to 267 CFUs/mL. Scavenged ice nucleators belong to a number of taxa including the bacterial genera Pseudomonas, Pantoea, and Xanthomonas, and the fungal genera Fusarium, Humicola, and Mortierella. An ice-nucleating strain of the fungal genus Penicillium was also recovered from a volumetric air sampler at the study site. This work expands our knowledge of the scavenging properties of rainfall, and suggests that at least some ice nucleators in natural precipitation events may have been scrubbed from the atmosphere during rainfall, and thus are not likely to be involved in precipitation.
Keywords: Precipitation; Scavenging; Scrubbing; Ice nucleation; Water cycle; Pseudomonas syringae;

New directions: Beyond sulphur, vanadium and nickel – About source apportionment of ship emissions in emission control areas by Hendryk Czech; Jürgen Schnelle-Kreis; Thorsten Streibel; Ralf Zimmermann (190-191).