Surface Black Carbon Research Articles

Filterable Redox Cycling Activity: A Comparison between Diesel Exhaust Particles and Secondary Organic Aerosol Constituents

The redox activity of diesel exhaust particles (DEP) collected from a light-duty diesel passenger car engine was examined using the dithiothreitol (DTT) assay. DEP was highly redox-active, causing DTT to decay at a rate of 23-61 pmol min(-1) μg(-1) of particle used in the assay, which was an order of magnitude higher than ambient coarse and fine particulate matter (PM) collected from downtown Toronto. Only 2-11% of the redox activity was in the water-soluble portion, while the remainder occurred at the black carbon surface. This is in contrast to redox-active secondary organic aerosol constituents, in which upward of 90% of the activity occurs in the water-soluble fraction. The redox activity of DEP is not extractable by moderately polar (methanol) and nonpolar (dichloromethane) organic solvents, and is hypothesized to arise from redox-active moieties contiguous with the black carbon portion of the particles. These measurements illustrate that "Filterable Redox Cycling Activity" may therefore be useful to distinguish black carbon-based oxidative capacity from water-soluble organic-based activity. The difference in chemical environment leading to redox activity highlights the need to further examine the relationship between activity in the DTT assay and toxicology measurements across particles of different origins and composition.

Evaluation of preindustrial to present-day black carbon and its albedo forcing from Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)

Abstract. As part of the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), we evaluate the historical black carbon (BC) aerosols simulated by 8 ACCMIP models against observations including 12 ice core records, long-term surface mass concentrations, and recent Arctic BC snowpack measurements. We also estimate BC albedo forcing by performing additional simulations using offline models with prescribed meteorology from 1996–2000. We evaluate the vertical profile of BC snow concentrations from these offline simulations using the recent BC snowpack measurements. Despite using the same BC emissions, the global BC burden differs by approximately a factor of 3 among models due to differences in aerosol removal parameterizations and simulated meteorology: 34 Gg to 103 Gg in 1850 and 82 Gg to 315 Gg in 2000. However, the global BC burden from preindustrial to present-day increases by 2.5–3 times with little variation among models, roughly matching the 2.5-fold increase in total BC emissions during the same period. We find a large divergence among models at both Northern Hemisphere (NH) and Southern Hemisphere (SH) high latitude regions for BC burden and at SH high latitude regions for deposition fluxes. The ACCMIP simulations match the observed BC surface mass concentrations well in Europe and North America except at Ispra. However, the models fail to predict the Arctic BC seasonality due to severe underestimations during winter and spring. The simulated vertically resolved BC snow concentrations are, on average, within a factor of 2–3 of the BC snowpack measurements except for Greenland and the Arctic Ocean. For the ice core evaluation, models tend to adequately capture both the observed temporal trends and the magnitudes at Greenland sites. However, models fail to predict the decreasing trend of BC depositions/ice core concentrations from the 1950s to the 1970s in most Tibetan Plateau ice cores. The distinct temporal trend at the Tibetan Plateau ice cores indicates a strong influence from Western Europe, but the modeled BC increases in that period are consistent with the emission changes in Eastern Europe, the Middle East, South and East Asia. At the Alps site, the simulated BC suggests a strong influence from Europe, which agrees with the Alps ice core observations. At Zuoqiupu on the Tibetan Plateau, models successfully simulate the higher BC concentrations observed during the non-monsoon season compared to the monsoon season but overpredict BC in both seasons. Despite a large divergence in BC deposition at two Antarctic ice core sites, some models with a BC lifetime of less than 7 days are able to capture the observed concentrations. In 2000 relative to 1850, globally and annually averaged BC surface albedo forcing from the offline simulations ranges from 0.014 to 0.019 W m−2 among the ACCMIP models. Comparing offline and online BC albedo forcings computed by some of the same models, we find that the global annual mean can vary by up to a factor of two because of different aerosol models or different BC-snow parameterizations and snow cover. The spatial distributions of the offline BC albedo forcing in 2000 show especially high BC forcing (i.e., over 0.1 W m−2) over Manchuria, Karakoram, and most of the Former USSR. Models predict the highest global annual mean BC forcing in 1980 rather than 2000, mostly driven by the high fossil fuel and biofuel emissions in the Former USSR in 1980.

The impact assessment of Diwali fireworks emissions on the air quality of a tropical urban site, Hyderabad, India, during three consecutive years

Diwali is one of the largest festivals for Hindu religion which falls in the period October-November every year. During the festival days, extensive burning of firecrackers takes place, especially in the evening hours, constituting a significant source of aerosols, black carbon (BC), organics, and trace gases. The widespread use of sparklers was found to be associated with short-term air quality degradation events. The present study focuses on the influence of Diwali fireworks emissions on surface ozone (O3), nitrogen oxides (NO x ), and BC aerosol concentration over the tropical urban region of Hyderabad, India during three consecutive years (2009-2011). The trace gases are analyzed for pre-Diwali, Diwali, and post-Diwali days in order to reveal the festivity's contribution to the ambient air quality over the city. A twofold to threefold increase is observed in O3, NO x , and BC concentrations during the festival period compared to control days for 2009-2011, which is mainly attributed to firecrackers burning. The high correlation coefficient (~0.74) between NO x and SO2 concentrations and higher SO2/NO x (S/N) index suggested air quality degradation due to firecrackers burning. Furthermore, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation-derived aerosol subtyping map also confirmed the presence of smoke aerosols emitted from firecrackers burning over the region. Nevertheless, the concentration level of pollutants exhibited substantial decline over the region during the years 2010 and 2011 compared to 2009 ascribed to various awareness campaigns and increased cost of firecrackers.

16‐year simulation of Arctic black carbon: Transport, source contribution, and sensitivity analysis on deposition

Arctic regional climate is influenced by the radiative impact of aerosol black carbon (BC) both in the atmosphere and deposited on the snow and ice covered surfaces. The NIES (National Institute for Environmental Studies) global atmospheric transport model was used, with BC emissions from mid‐latitude fossil fuel and biomass burning source regions, to simulate BC concentrations with 16 year period. The model‐simulated BC agreed well with the BC observations, including the trends and seasonality, at three Arctic sites: Alert (Nunavut, Canada), Barrow (Alaska, USA), and Zepplin, Ny‐Ålesund (Svalbard, Norway). The equivalent black carbon (EBC, absorption inferred BC) observations at the three Arctic locations showed an overall decline of 40% from 1990 to 2009; with most change occurring during early 1990s. Model simulations confirmed declining influence on near surface BC contribution by 70% , and atmospheric BC burden by one half from the Former Soviet Union (FSU) BC source region over 16 years. In contrast, the BC contribution from the East Asia (EA) region has little influence at the surface but atmospheric Arctic BC burden increased by 3 folds. Modelled dry deposition is dominant in the Arctic during wintertime, while wet deposition prevails at all latitudes during summer. Sensitivity analyses on the dry and wet deposition schemes indicate that parameterizations need to be refined to improve on the model performance. There are limitations in the model due to simplified parameterizations and remaining model uncertainties, which requires further exploration of source region contributions, especially from growing EA source region to Arctic BC levels in the future is warranted.

Seasonal variation of surface and vertical profile of aerosol properties over a tropical urban station Hyderabad, India

One year measurement of vertical profiles of volume backscatter and extinction coefficient, aerosol optical depth (AOD), mass concentration of black carbon (BC) and composite aerosol along with thermodynamic structure of the atmosphere has been carried out over an urban tropical location of Hyderabad(17.47°N, 78.58°E), India, during April 2009 to March 2010. The mean mixing layer height (MLH) exhibits large seasonality exceeding 4 km in pre‐monsoon period whereas in winter it comes down to ~1.5 km with an annual mean value of 2.35 ± 1.02 km. Surface BC mass fraction (FBC) shows marked seasonal variation from winter (13 ± 1.9%), pre‐monsoon (8.19 ± 2.16%), monsoon (7.3 ± 1.8%) to post‐monsoon (11.8 ± 0.18%). The profiles of volume backscatter and extinction coefficients reveal presence of elevated aerosol layers from 2 to 4 km and strong oscillations during pre‐monsoon (March–May) and monsoon (June–September) seasons, respectively, while in post‐monsoon (October–November) and winter (December–February), the aerosols are well within the lower boundary layer and also exhibit a drastic decrease with increasing altitude. These elevated aerosol layers and vertical distribution appear to be closely linked to the thermodynamic structure of the atmosphere. The aerosol optical properties in conjunction with air mass back trajectory analysis indicate that the observed elevated aerosol layers during pre‐monsoon and monsoon could contain significant fraction of coarse mode particles with a mix of dust and marine aerosols. Further analysis reveals that the aerosols within atmospheric boundary layer (ABL) dominate the column aerosol loading with ABL‐AOD contributing to ~77.7 ± 17.0%, with significant seasonal variation from winter (86.2 ± 13.1%), pre‐monsoon (76.6 ± 12.8%), monsoon (54.2 ± 15.6%) to post monsoon (80.8 ± 14.8%). Seasonal variation of ABL‐AOD and BC mass fraction follows similar pattern in the ABL indicating that BC may be an important contributor to the ABL aerosol loading.

Transport of black carbon to polar regions: Sensitivity and forcing by black carbon

The transport of black carbon (BC) to polar regions is studied using the University of Michigan IMPACT aerosol model driven by two sets of meteorological fields from the NCAR CAM5 and GFDL AM3 models. The sensitivity of the transport of BC to wet deposition processes is tested by varying the wet deposition in large‐scale precipitation. BC concentrations and deposition in polar regions are shown to be sensitive to both the meteorological fields and the wet deposition treatment. Using the default wet deposition, both IMPACT‐CAM5 and IMPACT‐AM3 simulate an appropriate amount of BC deposition in polar regions as compared to ice core observations. Although the seasonal cycle of BC surface air concentrations is reasonable, the concentrations are about 1∼2 orders of magnitude smaller than observations. With reduced wet deposition efficiency, the total deposition of BC increases by a factor of ∼2 to ∼3 due to more transport to the poles. The near surface BC concentrations increase even more (by a factor of ∼3 to ∼10) but are still largely underestimated especially in the north polar region. The radiative forcing from the BC deposited on snow and sea ice is also sensitive to the wet deposition treatment and the different meteorological fields. The global (Arctic) annual mean forcing is about +0.020 W m−2 (+0.11 W m−2) for IMPACT‐CAM5 and +0.022 W m−2 (+0.13W m−2) for IMPACT‐AM3.

Sources and radiative effects of wintertime black carbon aerosols in an urban atmosphere in east India

We carried out an analysis of black carbon (BC) surface mass concentration, its radiative effects, and sources of origin in an urban atmosphere in east India, during winter season, through ground-based measurements and application of modelling tools. BC surface mass concentration exhibited diurnal variation with their higher values and a larger variability during evening to early morning hours than during daytime (1100–1600h, Local Time, LT) hours. Daytime mean surface BC mass concentration and BC mass fraction in total aerosol (size range 0.23–20μm) and in submicronic aerosol (size range 0.23–1μm) during the study period, corresponding to the well-mixed atmospheric layer were 11μgm−3, 3–10%, and 9–16% respectively. The mean BC optical depth (BC-AOD) and BC-AOD fraction at 0.5μm were estimated in an optical model as 0.11 and 13% respectively. Mean shortwave aerosol radiative forcing due to BC at top-of-atmosphere (TOA) during the study period was found to be +0.94Wm−2, which is about 59% the global mean radiative forcing due to carbon-dioxide gases. Estimates from BC simulations in a general circulation model showed BC surface concentration and BC optical depth in east India are primarily attributed to emissions from biofuel and fossil fuel combustion. Most of BC surface concentration (95%) and BC optical depth (60%) are contributed by emissions arising from the Indo-Gangetic plain (IGP) but there is a significant influence to BC columnar loading through elevated transport channels attributed mainly to emissions from open biomass burning from distant regions outside IGP.

An overview of black carbon deposition in High Asia glaciers and its impacts on radiation balance

Since 2000, 18 High Asia glaciers have been surveyed for black carbon (BC) deposition 22 times, and numerous snow samples and ice cores have been collected by researchers. However, most of the results were interpreted individually in papers. Here, we assemble the data and discuss the distribution of BC deposition and its impacts on the melting of the glaciers through radiative forcing. We find that BC distribution on the surfaces of High Asia glaciers primarily depends upon their elevations (i.e., higher sites have lower concentrations) and then upon regional BC emissions and surface melting conditions. BC concentrations in High Asia glaciers are similar to the Arctic and western American mountains but are significantly less than heavy industrialized areas such as northern China. Although Himalayan glaciers, which are important due to their water resources, are directly facing the strong emissions from South Asia, their mean BC is the lowest due to high elevations. A new finding indicated by ice core records suggested that great valleys in the eastern Himalayan section are effective pathways for BC entering the Tibetan Plateau and make increasing BC trends in the local glaciers. On average, BC deposition causes a mean forcing of ∼6 Wm−2 (roughly estimated 5% of the total forcing) in High Asia glaciers and therefore may not be a major factor impacting the melting of most glaciers.

Sectoral and geographical contributions to summertime continental United States (CONUS) black carbon spatial distributions

The sectoral and regional contributions from northern hemisphere anthropogenic and biomass burning emission sectors to black carbon (BC) distributions over the continental United States (CONUS) in summer 2008 are studied using the Sulfur Transport and dEposition Model (STEM). North American (NA) emissions heavily (>70% of total emissions) affect the BC levels from the surface to w5 km, while non-NA plumes compose more than half of the BC above w5 km. Among all sectors, NA and non-NA biomass burning, NA transportation and non-NA residential emissions are the major contributors. The sectoral contributions vary among ten regions defined by the US Environmental Protection Agency (EPA): NA anthropogenic emissions enhance northeastern US BC levels; biomass burning strongly impacts northern California and southeastern US; and the influence of extra-regional plumes is largest in the northwestern US but extends to eastern US. The mean contribution from non-NA sources to US surface BC is w0.05 m gm �3 , with a maximum value of w0.11 m gm �3 in the northwestern US. The non-NA contributions to column BC are higher than to surface BC, ranging from 30% to 80%, depending on region. EPA region 8 is most sensitive to extra-regional BC, partially explaining the observed increasing BC trend there during the past decades associated with the increasing Asian BC emissions. Measurements from the June 24 DC-8 flight during the ARCTAS-CARB field campaign show that BC/(organic matter þ nitrate þ sulfate) mass ratios fairly well represent BC’s warming potential over southern California, which can be approximated by BC/(organic matter þ sulfate) and BC/sulfate for plumes affected and unaffected by fires, respectively. The responses of BC/(organic matter þ sulfate) and BC/sulfate to removing each emission sector are further discussed, indicating that mitigating NA transportation emissions has the highest potential for regional air quality and climate co-benefits.

A preliminary study on measurements of black carbon in the atmosphere of northwest Qilian Shan

Abstract Black carbon (BC) concentration and meteorological data are measured discontinuously from May 2009 to March 2011, at the Qilian Shan Station of Glaciology and Ecologic Environment (hereafter “QSSGEE”), located near the terminal of the Laohugou No.12 Glacier in northwestern Qilian Shan, China. We measured the daily, monthly and seasonal variations of BC concentration in the atmosphere and discussed the possible emission sources. Black carbon background concentration in this region varied in the range of 18-72 ng/m 3 with the highest in summer and the lowest in autumn. The relations between BC concentration and surface wind direction indicated that BC concentration was higher when northwest wind prevails while lower when southeast wind prevails. Air masses backward trajectories showed the potential emission sources in the northwest. Significant positive correlations between daily mean BC concentration and relative humidity indicated that BC might be one of important cloud condensation nuclei. This hypothesis needs to be confirmed further through cloud microphysical features in this region.

On board measurement of black carbon aerosols over the Arctic Ocean in summer

This paper presents aerosol black carbon (BC) concentrations measured at deck level on board the R/V XUE LONG icebreaker. The vessel cruised the Arctic Ocean carrying an in situ aethalometer during the summers of 2008 and 2010. The courses of the third Chinese National Arctic Research Expedition (3rd CHINAREArctic, August 2008) and fourth Chinese National Arctic Research Expedition (4th CHINARE-Arctic, from late July to August 2010) were bounded by 173°W-143°W and 178°E-150°W, with northernmost points 85°250N and 88°26′N, respectively. Results show low surface BC concentrations over the ocean throughout the courses, with means (standard error) of 6.0 (±4.7) ng·m -3 for 3rd CHINARE-Arctic, and 8.4(±7.1) ng·m -3 for 4th CHINAREArctic. It is clear that these onboard BC concentrations are similar to reported data from coastal stations in the Arctic region. The latitude-average BC concentration varied from 3.0-26.2 ng·m -3 for 3rd CHINARE-Arctic, to 4.2-20.5 ng·m -3 for 4th CHINARE-Arctic. At latitudes higher than 72°N for 3rd CHINARE-Arctic and 75°N for 4th CHINARE-Arctic, BC concentrations were lower and had negligible latitudinal gradients. Analysis indicates that the presence of the Arctic front isolates the lower atmosphere of the high-latitude Arctic Ocean from low-latitude terrestrial transport. This maintains the very low BC concentrations and negligible concentration gradients at high latitudes of the Arctic Ocean during summer. Calculated airmass backward trajectories for the two expeditions show that the Arctic front in 2010 was further north than in 2008, which caused different latitudinal variation of BC concentration in the two years.

Field-Scale Reduction of PCB Bioavailability with Activated Carbon Amendment to River Sediments

Remediation of contaminated sediments remains a technological challenge because traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Recent work has shown that uptake of persistent organic pollutants such as polychlorinated biphenyls (PCBs) in the food web is strongly influenced by the nature of contaminant binding, especially to black carbon surfaces in sediments. We demonstrate for the first time in a contaminated river that application of activated carbon to sediments in the field reduces biouptake of PCBs in benthic organisms. After treatment with activated carbon applied at a dose similar to the native organic carbon of sediment, bioaccumulation in freshwater oligochaete worms was reduced compared to preamendment conditions by 69 to 99%, and concentrations of PCBs in water at equilibrium with the sediment were reduced by greater than 93% at all treatment sites for up to three years of monitoring. By comparing measured reductions in bioaccumulation of tetra- and penta-chlorinated PCB congeners resulting from field application of activated carbon to a laboratory study where PCBs were preloaded onto activated carbon, it is evident that equilibrium sorption had not been achieved in the field. Although other remedies may be appropriate for some highly contaminated sites, we show through this pilot study that PCB exposure from moderately contaminated river sediments may be managed effectively through activated carbon amendment in sediments.

Biomass burning contribution to black carbon in the Western United States Mountain Ranges

Abstract. Forest fires are an important source to carbonaceous aerosols in the Western United States (WUS). We quantify the relative contribution of biomass burning to black carbon (BC) in the WUS mountain ranges by analyzing surface BC observations for 2006 from the Interagency Monitoring of PROtected Visual Environment (IMPROVE) network using the GEOS-Chem global chemical transport model. Observed surface BC concentrations show broad maxima during late June to early November. Enhanced potassium concentrations and potassium/sulfur ratios observed during the high-BC events indicate a dominant biomass burning influence during the peak fire season. Model surface BC reproduces the observed day-to day and synoptic variabilities in regions downwind of but near urban centers. Major discrepancies are found at elevated mountainous sites during the July-October fire season when simulated BC concentrations are biased low by a factor of two. We attribute these low biases largely to the underestimated (by more than a factor of two) and temporally misplaced biomass burning emissions of BC in the model. Additionally, we find that the biomass burning contribution to surface BC concentrations in the USA likely was underestimated in a previous study using GEOS-Chem (Park et al., 2003), because of the unusually low planetary boundary layer (PBL) heights in the GEOS-3 meteorological reanalysis data used to drive the model. PBL heights from GEOS-4 and GEOS-5 reanalysis data are comparable to those from the North American Regional Reanalysis (NARR). Model simulations show slightly improved agreements with the observations when driven by GEOS-5 reanalysis data, but model results are still biased low. The use of biomass burning emissions with diurnal cycle, synoptic variability, and plume injection has relatively small impact on the simulated surface BC concentrations in the WUS.

Influences of the springtime northern Indian biomass burning over the central Himalayas

The influences of the springtime northern Indian biomass burning are shown for the first time over the central Himalayas by using three years (2007-2009) of surface and space based observations along with a radiative transfer model. Near-surface ozone, black carbon (BC), spectral aerosol optical depths (AODs) and the meteorological parameters are measured at a high altitude site Nainital (29.37 degrees N, 79.45 degrees E, 1958 m amsl) located in the central Himalayas. The satellite observations include the MODIS derived fire counts and AOD (0.55 mu m), and OMI derived tropospheric column NO(2), ultraviolet aerosol index and single scattering albedo. MODIS fire counts and BC observations are used to identify the fire-impacted periods (372 h during 2007-2009) and hence the induced enhancements in surface BC, AOD (0.5 mu m) and ozone are estimated to be 1802 ng m(-3) (similar to 145%), 0.3 (similar to 150%) and 19 ppbv (similar to 34%) respectively. Large enhancements (53-100%) are also seen in the satellite derived parameters over a 2 degrees x 2 degrees region around Nainital. The present analysis highlights the northern Indian biomass burning induced cooling at the surface (-27 W m(-2)) and top of the atmosphere (-8 W m(-2)) in the lesser polluted high altitude regions of the central Himalayas. This cooling leads to an additional atmospheric warming of 19 W m(-2) and increases the lower atmospheric heating rate by 0.8 K day(-1). These biomass burning induced changes over the central Himalayan atmosphere during spring may also lead to enhanced short-wave absorption above clouds and might have an impact on the monsoonal rainfall.

Anthropogenic impact on the temporal variations of black carbon and surface aerosol mass concentrations at a tropical semi-arid station in southeastern region of India

Collocated measurements of black carbon (BC) and composite aerosol mass concentrations were continuously monitored at Anantapur (14.62°N, 77.65°E, 331 m asl), a tropical semi-arid station in southeastern region of India, using Aethalometer and a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor, respectively during August 2009–July 2010. Diurnal and seasonal variations of BC and near surface aerosols in relation to changes in the regional meteorological conditions, frequency distribution of BC for different seasons, week days and weekend days effect on BC concentration and size distributions of near surface aerosols were observed. Also, using the HYSPLIT model, back-trajectories were studied to assess the sources for transported particles. Diurnal variation of BC showed two peaks, one in the morning and another in the evening, which were mostly related to the daily changes in the local boundary layer. BC concentrations were maximum during the winter (4.76 ± 0.97 μg m −3), and minimum concentrations were observed in the monsoon (1.44 ± 0.26 μg m −3). The total mass concentration exhibits a high value in the summer (48.89 ± 2.57 μg m −3) and it remains low in the monsoon (30.33 ± 1.65 μg m −3) period. The maximum BC mass fraction was found to be 9.4% in the winter and a minimum of 4.6% in the monsoon.

The influence of acid demineralization on surface characteristics of black carbon and its sorption for pentachlorophenol

Acid treatment is a routine demineralization process to obtain black carbon (BC), but there has been little systematic research about its influence on BC’s characteristics. In this study, elemental analysis, SEM, FTIR, and Boehm titration were used to investigate that effect. Our results showed that the acid treatment had little influence on the sorption of fly ash and soot to pentachlorophenol (PCP), but it greatly increased the sorption of rice chars to PCP. There were two competing effects of acid demineralization on the adsorption capacity of BC. On one hand, it increased the amount of the acidic functional groups, which decreased the adsorption capacity. On the other hand, it increased the surface and pore volume of BC and caused the emergence of hidden carbon enclosed by minerals, which in turn increased the sorptivity significantly. Especially for rice chars (600°C), after acid treatment, their surface area increased from 3.52 to 235m2g−1 and the sorption capacity coefficient increased from 2.12 to 4.10.

Effect of Surfactants on Sorption and Desorption of Phenanthrene onto Black Carbon

Sorption and desorption of phenanthrene onto black carbon extracted from sediment were studied in the presence of a cationic surfactant (cetyltrimethylammonium bromide [CTAB]), an anionic surfactant (sodium dodecylbenzene sulfonate [SDBS]), and a nonionic surfactant (Triton X-100 [TX100]), to examine the role of surfactants in sorption and desorption. Nonlinearity of the sorption isotherms increased in the presence of surfactants. The CTAB enhanced the sorption capacity and irreversibility of phenanthrene on black carbon. However, the presence of SDBS reduced the sorption capacity and desorption hysteresis. Unlike CTAB and SDBS, the influence of TX100 on sorption was concentration-dependent. Low levels of TX100 increased sorption, as a result of the sorption of TX100 on the black carbon surface. High levels of TX100 led to a decrease in sorption because of the solubilization of phenanthrene in TX100 solution. Our results may help to understand the different effects of surfactants on the distribution and transport of polycyclic aromatic hydrocarbons in the environment.

Relative contributions of anthropogenic emissions to black carbon aerosol in the Arctic

Using a global air quality model with online aerosol algorithm GEM‐AQ, this work first validates the performance of the model against available observations and then estimates the regional contributions to the Arctic black carbon (BC) aerosol from anthropogenic sources. The comparisons against the surface measurements at Alert and Zeppelin suggest that the Arctic BC aerosol can be predicted by the model within 15% on annual average, and the seasonality of Arctic BC is predicted by 90% and 66% at these sites, respectively. Comparisons against surface measurements in North America, Europe, and South Asia confirm that surface BC concentrations are reproduced by the model within a factor of 2 at most (104 out of 115) sites investigated. Using GEM‐AQ, sensitivity experiments are conducted by reducing the anthropogenic emissions from selected regions by 20%. Based on area‐weighted results for the Arctic region, model simulations suggest that Europe contributes more (up to 57%) to the lowest 5 km of the Arctic troposphere than any other region. The contribution of Asian Russia is significant near the surface (about 30% at 100 m above the surface) and decreases rapidly to less than 10% at the altitude of about 5 km in the Arctic troposphere. The contributions from South and East Asia increase with increasing altitude, and become more significant than others in the upper troposphere and the lower stratosphere, with their peak contributions of about 35% and 40%, respectively. North American contribution to the Arctic troposphere (about 10–20%) has the least variations in the vertical direction among the potential source regions affecting the Arctic.

Investigation on the direct radiative effect of fossil fuel black-carbon aerosol over China

In China, due to lack of countrywide monitoring and coarse emission inventory of black carbon (BC) in early years, there are large uncertainties as to the estimations of its loading, direct radiative forcing (DRF) and climate response. Here, we apply an up-to-date emission inventory of BC in 2006 to investigate its loading, optical depth (AOD) at 550 nm and DRF using the coupled Regional Climate Chemistry Modeling System (RegCCMS). A state of the art air quality model (WRF/Chem) is also used to access surface BC concentration. Simulated surface concentrations of BC from these two models were compared with observations, while the AOD was compared with the results both from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and from satellite and ground-based simulations. Results show that RegCCMS presented similar patterns and levels of annual mean-surface BC concentration to those of WRF/Chem. The regional distributions and monthly variations of RegCCMS BC were reproduced well in comparison to observations. Simulated pattern of AODs are consistent to but lower than those from satellite (Omi-0.25°) and AERONET simulations. Annual mean DRFs mainly distribute in the area with high BC loadings, with regional mean of 0.75 W m–2 and predicted global mean of 0.343 W m–2. In general, the results are about 0.4–5 times for regional column burden, about 2 times as high for regional mean DRFs, about 1.3–1.8 times for global mean DRFs and about 3–4 times for AOD at 550 nm as compared to those in previous studies in China. These increasing DRFs of BC imply that its warming effect and climate response should be stronger and the DRF of total aerosols should be weaker (less negative).

The pH-dependent adsorption of tributyltin to charcoals and soot

Widespread use of tributyltin (TBT) poses a serious environmental problem. Adsorption by black carbon (BC) may strongly affect its behavior. The adsorption of TBT to well characterized soot and two charcoals with specific surface area in the range of 62–111 m 2 g −1 have been investigated with main focus on pH effects. The charcoals but not soot possess acidic functional groups. TBT adsorption reaches maximum at pH 6–7 for charcoals, and at pH > 6 for soot. Soot has between 1.5 and 15 times higher adsorption density (0.09–1.77 μmol m −2) than charcoals, but charcoals show up to 17 times higher sorption affinities than soot. TBT adsorption is successfully described by a new pH-dependent dual Langmuir model considering electrostatic and hydrophobic adsorption, and pH effects on TBT speciation and BC surface charge. It is inferred that strong sorption of the TBTOH species to BC may affect TBT toxicity.