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The dual carbon isotope signatures and optical properties of carbonaceous aerosols have been investigated simultaneously for the first time in the South Asian outflow during an intensive campaign at the Maldives Climate Observatory on Hanimaadhoo (MCOH) (February and March 2012). As one component of the Cloud Aerosol Radiative Forcing Dynamics Experiment, this paper reports on the sources and the atmospheric processing of elemental carbon (EC) and water-soluble organic carbon (WSOC) as examined by a dual carbon isotope approach. The radiocarbon (Δ14C) data show that WSOC has a significantly higher biomass/biogenic contribution (86 ± 5%) compared to EC (59 ± 4%). The more13C-enriched signature of MCOH-WSOC (20.8 ± 0.7‰) compared to MCOH-EC (25.8 ± 0.3‰) and megacity Delhi WSOC (24.1 ± 0.9‰) suggests that WSOC is significantly more affected by aging during long-range transport than EC. The δ13 C-Δ14 C signal suggests that the wintertime WSOC intercepted over the Indian Ocean largely represents aged primary biomass burning aerosols. Since light-absorbing organic carbon aerosols (Brown Carbon (BrC)) have recently been identified as potential contributors to positive radiative forcing, optical properties of WSOC were also investigated. The mass absorption cross section of WSOC (MAC365) was 0.5 ± 0.2 m2 g1 which is lower than what has been observed at near-source sites, indicating a net decrease of WSOC light-absorption character during long-range transport. Near-surface WSOC at MCOH accounted for ~1% of the total direct solar absorbance relative to EC, which is lower than the BrC absorption inferred from solar spectral observations of ambient aerosols, suggesting that a significant portion of BrC might be included in the water-insoluble portion of organic aerosols.

This study presents and evaluates the most comprehensive set to date of chemical, physical and optical properties of aerosols in the outflow from South Asia covering a full winter (Nov. 2014 - March 2015), here intercepted at the Indian Ocean receptor site of the Maldives Climate Observatory in Hanimaadhoo (MCOH). Cluster analysis of air-mass back trajectories for MCOH, combined with AOD and meteorological data, demonstrate that the wintertime northern Indian Ocean is strongly influenced by aerosols transported from source regions with three major wind regimes, originating from the Indo-Gangetic Plain (IGP), the Bay of Bengal (BoB) and the Arabian Sea (AS). As much as 97 ± 3% of elemental carbon (EC) in the PM10 was also found in the fine mode (PM2.5). Other mainly anthropogenic constituents such as organic carbon (OC), non-sea-salt (nss) -K+, nss-SO42− and NH4+ were also predominantly in the fine mode (70-95%), particularly in the air masses from IGP. The combination at this large-footprint receptor observatory of consistently low OC/EC ratio (2.0 ± 0.5), strong linear relationships between EC and OC as well as between nss-K+ and both OC and EC, suggest a predominance of primary sources, with a large biomass burning contribution. The particle number-size distributions for the air masses from IGP and BoB exhibited clear bimodal shapes within the fine fraction with distinct accumulation (0.1 μm < d < 1 μm) and Aitken (0.025 μm < d < 0.10 μm) modes. This study also supports that IGP is a key source region for the wider South Asia and nearby oceans, as defined by the criteria that anthropogenic AODs exceed 0.3 and absorption AOD > 0.03. Taken together, the aerosol pollution over the northern Indian Ocean in the dry season is dominated by a well-mixed long-range transported regime of the fine-mode aerosols largely from primary combustion origin. [ABSTRACT FROM AUTHOR]

Black carbon (BC) plays an important role in carbon burial in marine sediments globally. Yet the sequestration of BC in the Arctic Ocean is poorly understood. Here we assess the concentrations, fluxes, and sources of soot BC (SBC)-the most refractory component of BC-in sediments from the East Siberian Arctic Shelf (ESAS), the World's largest shelf sea system. SBC concentrations in the contemporary shelf sediments range from 0.1 to 2.1 mg g−1 dw, corresponding to 2-12% of total organic carbon. The 210Pb-derived fluxes of SBC (0.42-11 g m−2 yr−1) are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions. The total burial flux of SBC in the ESAS (~4,000 Gg yr−1) illustrates the great importance of this Arctic shelf in marine sequestration of SBC. The radiocarbon signal of the SBC shows more depleted yet also more uniform signatures (−721 to −896‰; average of −774 ± 62‰) than of the non-SBC pool (−304 to −728‰; average of −491 ± 163‰), suggesting that SBC is coming from an, on average, 5,900 ± 300 years older and more specific source than the non-SBC pool. We estimate that the atmospheric BC input to the ESAS is negligible (~0.6% of the SBC burial flux). Statistical source apportionment modeling suggests that the ESAS sedimentary SBC is remobilized by thawing of two permafrost carbon (PF/C) systems: surface soil permafrost (topsoil/PF; 25 ± 8%) and Pleistocene ice complex deposits (ICD/PF; 75 ± 8%). The SBC contribution to the total mobilized permafrost carbon (PF/C) increases with increasing distance from the coast (from 5 to 14%), indicating that the SBC is more recalcitrant than other forms of translocated PF/C. These results elucidate for the first time the key role of permafrost thaw in the transport of SBC to the Arctic Ocean. With ongoing global warming, these findings have implications for the biogeochemical carbon cycle, increasing the size of this refractory carbon pool in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Atmospheric black carbon (BC) is an important pollutant for both air quality and Earth's energy balance. Estimates of BC climate forcing remain highly uncertain, e.g., due to the mixing with non-absorbing components. Non-absorbing aerosols create a coating on BC and may thereby act as a lens which may enhance the light absorption. However, this absorption enhancement is poorly constrained. To this end a two-step solvent dissolution protocol was employed to remove both organic and inorganic coatings, and then investigate their effects on BC light absorption. Samples were collected at a severely polluted urban area, Jinan, in the North China Plain (NCP) during February 2014. The BC mass absorption cross-section (MAC) was measured for the aerosol samples before and after the solvent-decoating treatment, and the enhancement of MAC ( E MAC ) from the coating effect was defined as the ratio. A distinct diurnal pattern for the enhancement was observed, with E MAC 1.3 ± 0.3 (1 S.D.) in the morning, increasing to 2.2 ± 1.0 in the afternoon, after that dropping to 1.5 ± 0.8 in the evening-night. The BC absorption enhancement primarily was associated with urban-scale photochemical production of nitrate and sulfate aerosols. In addition to that, regional-scale haze plume with increasing sulfate levels strengthened the absorption enhancement. These observations offer direct evidence for an increased absorption enhancement of BC due to severe air pollution in China. [ABSTRACT FROM AUTHOR]

Black carbon, which is a by-product of incomplete combustion of carbon containing fuels, can alter atmospheric radiation property and make adverse impacts on human health. This paper shows the comparative study of particles and associated gaseous pollutants measurements at five observatories dispersed across central part of megacity Delhi, India, with high-temporal resolution (5 min) measurements. The mean ± SD concentrations of black carbon (BC), fine particles (PM), carbon monoxide (CO), and oxides of nitrogen (NO) of the all five stations were 13.4 ± 10, 149.6 ± 109 µg m, 3.4 ± 2 ppm, and 81.8 ± 79 ppb, respectively. The mean mass concentration of PM was approximately four times and ten times in excess of annual average standards of Indian air quality (40 µg m) and USEPA (15 µg m) levels. Highest BC mass concentrations were recorded during winter (December) due to consistent with a shallower atmospheric boundary layer, lower wind speeds, and possibly larger biofuel burning in the coldest period. Also, the strong diurnal dynamics in boundary layer height had a large impact on the ground-level concentrations of all the pollutants. A significant difference in the emissions of atmospheric pollutants was observed over Delhi during weekdays and weekends during study period. There was a strong diurnal effect on BC and the other pollutants, presumably with mixing height as a strong driver. The 24-h cycle is characterized throughout the study by maximum concentrations around midnight and lowest concentrations at 1500-1700 hours local time (LT), with a local maximum between 0800 and 1000 hours LT, presumably due to morning rush hour. While the amplitude of the BC excursion was a factor of 2-3, the mixing height decreased by a factor of 12-14 from day to night. This monitoring program contributed to insights into the levels and dynamics of atmospheric pollutants in the New Delhi megacity over a 5-month period. The concentrations are varying over several timescales, consistent with both atmospheric mixing and variations in presumed emission source strengths. [ABSTRACT FROM AUTHOR]

The thin organic film that builds up on the exterior surface of windows has been proposed as a ubiquitously available passive sampler for semi-volatile organic contaminants (SOCs) in urban air. Readily available school windows were sampled in Stockholm city centre and suburban locations in both winter and summer season to evaluate the putative usefulness of this matrix for assessing the integrated load of urban air pollution by polycyclic aromatic hydrocarbons (PAHs). The window-area normalised concentrations indicated more PAH contamination in the winter than in the summer in both the city centre and suburban locations, with highest concentrations in the city centre in the winter (∑PAH43 451–467ngm−2). However, normalising the PAH load to the amount of fatty window film, as measured by extractable organic matter (EOM), gave a more homogeneous picture with the EOM-normalised PAH load being inseparable both between summer and winter and between city centre and suburban locations. To evaluate the possibility of quantitatively employing urban window films as a means to provide predicted environmental concentrations of PAHs in air (PECair), window film–air partition coefficients of PAHs were estimated using a set of coupled linear free energy relationships and physico-chemical properties of PAHs. Assuming dynamic equilibria between PAHs in air and dissolved in the window film, the obtained PECair from the window films were consistently overestimating the urban vapour-phase PAH concentrations by factors 4–135. This discrepancy is quantitatively consistent with a strong and overwhelming association with black carbon aerosol particles accumulated in the window film. For SOCs that have a lower tendency to associate with black carbon, bulk window film concentrations may work better than for PAHs to estimate their vapour-phase concentrations in urban air. [Copyright &y& Elsevier]

Abstract: Black carbon (BC; soot and charcoal) can be an extremely strong sorbent for organic compounds. In a previous study, sorption of d 10-phenanthrene (d 10-PHE) to BC in an unmodified contaminated sediment was found to be nine times less than that for BC isolated from this sediment. To find out the mechanism of this sorption attenuation (competition for BC sites between d 10-PHE and native PAHs or blocking of BC sites by natural organic matter), we determined the effect on d 10-PHE-BC sorption isotherms of additions of either PAHs or precipitated humic acid. Addition of humic acid did not significantly decrease BC sorption, whereas PAH additions (equal to the native PAH content in the original sediment) did, by about one order of magnitude. Therefore, competition between d 10-PHE and the native PAHs could explain the whole attenuation of sorption to BC in unmodified sediments. [Copyright &y& Elsevier]

The significance of black carbon (BC) for the bioavailability of polycyclic aromatic hydrocarbons (PAHs) was examined by using historically contaminated intact sediment cores in laboratory exposure experiments with the deposit-feeding amphipod Monoporeia affinis. Log values of amphipod biota-sediment accumulation factors (BSAFs) were significantly related to log BC, whereas log BSAFs were related to log octanol-water partition coefficients only in background sediments containing less BC. In the background sediments, the BSAF for polycyclic aromatic hydrocarbons (PAHs) was 1 to 2 for phenanthrene, with lower values for more hydrophobic PAHs, indicating an increase in nonequilibrium conditions with increasing PAH molecular size. For the nearequilibrated phenanthrene and fluoranthene, higher BSAFs were measured during exposure to background sediments, with BSAF decreasing to <0.1 in contaminated sediments in the Stockholm waterways. In situ caged mussels (Dreissena polymorpha) exhibited field BSAF values (relative to sediment-trap-collected suspended matter) for polychlorinated biphenyls (PCBs) of 0.1 to 0.4, but for PAHs of similar hydrophobicity and molecular size, the field BSAFs were much lower and in the range 0.002 to 0.05. This PAH-PCB dichotomy is consistent with recently reported much stronger binding to diesel soot (a form of BC) for PAHs than for PCBs of equal hydrophobicities. Lower BSAFs for the near-equilibrated PAHs (phenanthrene and fluoranthene) in the urban sediments relative to the background sediments were consistent with the larger presence of BC in the urban sediments. This study provides the first linked BSAF-BC field data that supports a causal relationship between strong soot sorption and reduced bioavailability for PAHs. [ABSTRACT FROM AUTHOR]

Field-observations of distribution coefficients well above expectations from bulk organic-matter partitioning for several chlorinated aromatic compound classes have lead to the hypothesis that enhanced affinity to soot may not be limited to polycyclic aromatic hydrocarbons but may extend as a significant process for a wider range of hydrophobic organic compounds. This suggestion was here tested in soot–column sorption experiments with a series of ortho- and non-ortho substituted polychlorinated biphenyls (PCBs), using diesel particulate matter (NIST standard reference material SRM-1650) as model soot sorbent. For congeners of similar hydrophobicity, considerably higher affinities toward the soot sorbent were observed for the non-ortho substituted PCBs. Mono- to tetra-ortho substituted PCBs exhibited log-based soot–water distribution coefficients (Ksc) from 5.25 to 5.51 l/kgsc at solute concentrations corresponding to 1–13 μg/l. In contrast, biphenyl, mono- and dichloro- non-ortho substituted PCBs yielded logKsc values between 5.09 and 6.35 l/kgsc. These results are 20–50, and 75–110 times higher, respectively, than the corresponding Kow-predicted Koc numbers. This strong interaction with soot, particularly of non-ortho substituted PCBs, may fundamentally affect their environmental distribution and bioavailable exposure. [Copyright &y& Elsevier]

Despite much recent efforts, the emission sources of black carbon (BC) aerosols―central input to understanding and predicting environmental and climate impact―remain highly uncertain. Here we present observational δ13C/Δ14C‐based constraints on the sources of BC aerosols over the four seasons in each of the four key hot spot emission regions of China: Beijing‐Tianjin‐Hebei (BTH‐Wuqing; where Wuqing is the sampling location), Yangtze River Delta (YRD‐Haining), Pearl River Delta (PRD‐Zhongshan), and Sichuan Basin (SC‐Deyang). Overall, BC loadings were highest in winter, yet elevated loadings were also observed in other seasons, for example, spring at SC‐Deyang and fall at PRD‐Zhongshan. Annually, the dominant BC sources were coal (50 ± 20%) for BTH‐Wuqing, liquid fossil for YRD‐Haining (46 ± 8%) and PRD‐Zhongshan (48 ± 18%), whereas liquid fossil (42 ± 17%) and biomass burning (41 ± 14%) equally affected SC‐Deyang. There is also different but distinct seasonalities in BC sources for the different sites. As an example, for BTH‐Wuqing coal burning increased from summer to winter, while summer and spring BTH‐Wuqing were more influenced by liquid fossil. In contrast, for YRD‐Haining, the relative importance of emission sources was more constant over the year. These quantitative observational constraints on source‐seasonality of BC aerosols in receptor sites located in China's four key economic zones highlight that regulatory control on BC aerosol emissions from different fuels should consider both seasonal and regional variations. Our results also suggest that models on estimates of BC‐induced climate and air quality should consider variations over both regional and seasonal scales. Key Points: Our observation‐based results show a strong source seasonality of black carbon aerosol for BTH, PRD, and SC, while little variation for YRDAnnually, the dominant BC sources are coal for BTH, liquid fossil for YRD and PRD, whereas SC is dominated by biomass and liquid fossil fuelsOur results suggest that regionally seasonally tailored mitigation strategies are crucial to effectively reducing aerosol pollution in China [ABSTRACT FROM AUTHOR]

Biota-to-sediment accumulation factors (BSAFs) sometimes show large variations between sites for a given planar hydrophobic organic compound (pHOC) in a given organism. We present a framework in which strong adsorption to soot/charcoal (black carbon [BC]) explains such BSAF variations. Recently constrained parameters on environmental BC sorption were used in a dual-mode sorption model of BSAF. Variations in sedimentary BC content are shown to explain variations in BSAF of one to two orders of magnitude. In addition, strong BC sorption can explain the often-observed difference in BSAF between polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The strong nonlinearity of BC sorption can render BSAF values strongly concentration-dependent for a given sediment/organism/compound combination, so it is of paramount importance to carry out uptake and toxicity tests at the relevant environmental concentrations. [ABSTRACT FROM AUTHOR]

Abstract: A growing literature proposes that combusted-derived black carbon (BC) dominates the sorption and, by inference, the environmental distribution and bioavailability of many hydrophobic pollutant classes. There is a paucity of studies simultaneously evaluating the distribution of both BC geosorbents and pollutant sorbates in the actual field. Here, 120 surface sediments collected by the Geological Survey of Sweden along the 2000km continental shelf along the Swedish coast facilitated evaluation of the relative influences of BC and non-BC organic carbon (OC) on the spatial distribution of polycyclic aromatic hydrocarbons (PAHs). The sum of 15 out of the 16 EPA PAHs ranged from 0.12 to 9.6μg/g dry weight (dw), with the highest levels being found in the southern half of the Swedish Shelf (SS) area and in the vicinity of larger cities (Stockholm, Göteborg, Malmö and Umeå). Source-diagnostic PAH ratios such as ANT/(PHE+ANT), FLT/(FLT+PYR), BaA/(BaA+BPE), IPY/(IPY+BPE), CombPAH/ΣPAH and LMW/HMW suggested that pyrogenic sources are dominating the load of PAHs in Swedish Baltic and North Sea sediments. The sediment TOC was 4.8–168mg/gdw (median 43mg/gdw), while a BC concentration of 0.6–18mg/gdw (median 1.8mg/gdw) yielded BC:TOC ratios spanning a wide range of 1.7–47% (median 4.6%). Empirical distribution function tests indicated that the use of linear regression statistics was inappropriate. Instead, evaluation with the non-parametric Spearman function yielded higher correlation coefficient (r S) for total PAHs versus BC (0.54, p <0.01) than versus either TOC (0.28, p <0.01) or OC (TOC-BC; 0.26, p <0.01). The results from this field study, encompassing an order of magnitude more observations than any previous sediment study, constitute a broad field manifestation of the importance of BC in affecting the distribution of planar aromatic pollutants in aquatic environments. [Copyright &y& Elsevier]

Abstract: A multi-media model was developed for predicting the fate of organic chemicals in the Greater Stockholm Area, Sweden, and applied to selected polycyclic aromatic hydrocarbons (PAHs). Although urban models have been previously developed, this model is novel in that it includes sorption to pyrogenically-derived particles, commonly termed “black carbon” (BC), within the model structure. To examine the influence of BC sorption on environmental fate of PAHs, two versions of the model were generated and run: one in which sorption to BC was included and one in which BC sorption was excluded. The inclusion of BC sorption did not cause any significant variations to air levels, but it did cause an average 20–30% increase in sediment concentrations related to increased sediment solids partitioning. The model also predicted reduced advective losses out of the model domain, as well as chemical potential to diffuse from sediments, whilst total chemical inventory increased. In all cases, the lighter PAHs were more affected by BC inclusion than their heavier counterparts. We advocate the addition of sorption to BC in future multi-media fate and exposure models, which as well as influencing fate will also alter (lower) chemical availability and, thus, wildlife exposure to hydrophobic chemicals. A quantification of the latter was derived with the help of the soot-inclusive model version, which estimated a lowering of dissolved water concentrations between five and >200 times for the different PAHs of this study. [Copyright &y& Elsevier]

To make progress towards linking the atmosphere and biogeosphere parts of the black carbon (BC) cycle, a chemothermal oxidation method (CTO-375), commonly applied for isolating BC from complex geomatrices such as soils, sediments and aquatic particles, was applied to investigate the BC also in atmospheric particles. Concentrations and 14C-based source apportionment of CTO-375 based BC was established for a reference aerosol (NIST RM-8785) and for wintertime aerosols collected in Stockholm and in a Swedish background area. The results were compared with thermal–optical (OC/EC) measurements. For NIST RM-8785, a good agreement was found between the BCCTO-375 concentration and the reported elemental carbon (EC) concentration measured by the “Speciation Trends Network—National Institute of Occupational Safety and Health” method (ECNIOSH) with BCCTO-375 of 0.054±0.002gg−1 and ECNIOSH of 0.067±0.008gg−1. In contrast, there was an average factor of ca. 20 difference between BCCTO-375 and ECNIOSH for the ambient Scandinavian wintertime aerosols, presumably reflecting a combination of BCCTO-375 isolating only the recalcitrant soot-BC portion of the BC continuum and the ECNIOSH metric inadvertently including some intrinsically non-pyrogenic organic matter. Isolation of BCCTO-375 with subsequent off-line radiocarbon analysis yielded fraction modern values (fM) for total organic carbon (TOC) of 0.93 (aerosols from a Swedish background area), and 0.58 (aerosols collected in Stockholm); whereas the fM for BCCTO-375 isolates were 1.08 (aerosols from a Swedish background area), and 0.87 (aerosols collected in Stockholm). This radiocarbon-based source apportionment suggests that contribution from biomass combustion to cold-season atmospheric BCCTO-375 in Stockholm was 70% and in the background area 88%. [Copyright &y& Elsevier]

In this study, we estimated the contribution of black carbon (BC) and brown carbon (BrC) to aerosol light absorption from surface in-situ and aerosol robotic network (AERONET) columnar observations. The mass absorption cross-section (MAC) of BC ( MAC BC ) was estimated to be 6.4 ± 1.5 m2 g−1 at 565 nm from in-situ aerosol measurements at Gosan Climate Observatory (GCO), Korea, in January 2014, which was lower than those observed in polluted urban areas. A BrC MAC of 0.62 ± 0.06 m2 g−1 (565 nm) in our estimate is approximately ten times lower than MAC BC at 565 nm. The contribution of BC and BrC to the carbonaceous aerosol absorption coefficient at 565 nm from the in-situ measurements was estimated at 88.1 ± 7.4% and 11.9 ± 7.4%, respectively at GCO. Similarly, the contribution of BC and BrC to the absorption aerosol optical depth (AAOD) for carbonaceous aerosol (CA), constrained by AERONET observations at 14 sites over East Asia by using different spectral dependences of the absorption (i.e., absorption Ångström exponent) of BC and BrC, was 84.9 ± 2.8% and 15.1 ± 2.8% at 565 nm, respectively. The contribution of BC to CA AAOD was greater in urban sites than in the background areas, whereas the contribution of BrC to CA AAOD was higher in background sites. The overall contribution of BC to CA AAOD decreased by 73%–87% at 365 nm, and increased to 93%–97% at 860 nm. The contribution of BrC to CA AAOD decreased significantly with increasing wavelength from approximately 17% at 365 nm to 4% at 860 nm. • We estimated the contribution of black carbon (BC) and brown carbon (BrC) to aerosol light absorption. • We used surface in-situ and column AERONET data from Gosan in January 2014. • The contribution of BC and BrC at 565 nm was estimated at 88.1±7.4% and 11.9±7.4%. • The contribution of BC and BrC to AAOD was 84.9±2.8% and 15.1±2.8%, respectively. • The contribution of BC to CA AAOD was greater in urban sites than in the background areas, whereas the contribution of BrC to CA AAOD was higher in background sites. [ABSTRACT FROM AUTHOR]

Polyaromatic organic matter (POM) is an important group of pollutants and light absorbers in ambient aerosols, which consists of a wide range of chemicals with fused benzene rings. POM in ambient aerosols is mainly derived from the incomplete combustion of fossil fuel and biomass. Source apportionment of POM is crucial for advising efficient mitigation of anthropogenic emissions, but that is a challenge due to the complicated composition of POM and ambient aerosols. Benzene polycarboxylic acids (BPCAs) have recently been introduced as molecular markers of atmospheric POM. Compound-specific radiocarbon analysis of BPCAs is expected to be a powerful tool for apportioning fossil sources and contemporary (i.e., biomass burning) sources of POM in ambient aerosols, yet this application is still lacking. We developed a method for radiocarbon analysis of BPCAs substituted with 3–6 carboxylic groups (B6CA, B5CA, B4CAs and B3CAs). BPCAs were isolated with preparative liquid chromatography with high recoveries (≥85%). The method is validated with reference materials with fossil and contemporary radiocarbon signatures. Successful radiocarbon analysis of BPCAs was achieved for these reference materials after correcting for the presence of average blanks (B6CA: 1.2 ± 0.2 μg, B5CA: 2.3 ± 0.6 μg, individual B4CAs: 2.7 ± 0.2 μg and individual B3CAs: 6.9 ± 0.7 μg). Source apportionment of POM based on radiocarbon analysis of BPCAs was performed for an urban dust reference material, as well as bulk aerosols and water-soluble, methanol-soluble fractions of ambient aerosols from a megacity of southern China. The results show varied contributions of fossil and contemporary sources among different POM fractions. [Display omitted] • Benzene polycarboxylic acids (BPCAs) are used to track polyaromatic organic matter (POM). • A method of compound-specific radiocarbon analysis (CSRA) of BPCAs is developed. • Successful CSRA of BPCAs is achieved for reference and ambient materials. • Sources of POM in ambient aerosols are apportioned by CSRA of BPCAs. • Fossil-contemporary source patterns vary between different POM fractions. [ABSTRACT FROM AUTHOR]

Regional haze over China has severe implications for air quality and regional climate. To effectively combat these effects the high uncertainties regarding the emissions from different sources needs to be reduced. In this paper, which is the third in a series on the sources of PM 2.5 in pollution hotspot regions of China, we focus on the sources of black carbon aerosols (BC), using carbon isotope signatures. Four-season samples were collected at two key locations: Beijing-Tianjin-Hebei (BTH, part of Northern China plain), and the Pearl River Delta (PRD). We find that that fossil fuel combustion was the predominant source of BC in both BTH and PRD regions, accounting for 75 ± 5%. However, the contributions of what fossil fuel components were dominating differed significantly between BTH and PRD, and varied dramatically with seasons. Coal combustion is overall the all-important BC source in BTH, accounting for 46 ± 12% of the BC in BTH, with the maximum value (62%) found in winter. In contrast for the PRD region, liquid fossil fuel combustion (e.g., oil, diesel, and gasoline) is the dominant source of BC, with an annual mean value of 41 ± 15% and the maximum value of 55% found in winter. Region- and season-specific source apportionments are recommended to both accurately assess the climate impact of carbonaceous aerosol emissions and to effectively mitigate deteriorating air quality caused by carbonaceous aerosols. [ABSTRACT FROM AUTHOR]

The radiative absorption enhancement of ambient black carbon (BC), by light-refractive coatings of atmospheric aerosols, constitutes a large uncertainty in estimates of climate forcing. The direct measurements of radiative absorption enhancement require the experimentally-removing the coating materials in ambient BC-containing aerosols, which remains a challenge. Here, the absorption enhancement of the BC core by non-absorbing aerosol coatings was quantified using a two-step removal of both inorganic and organic matter coatings of ambient aerosols. The mass absorption cross-section (MAC) of decoated/pure atmospheric BC aerosols of 4.4 ± 0.8 m 2 g − 1 was enhanced to 9.6 ± 1.8 m 2 g − 1 at 678-nm wavelength for ambiently-coated BC aerosols at a rural Northern China site. The enhancement of MAC ( E MAC ) rises from 1.4 ± 0.3 in fresh combustion emissions to ~ 3 for aged ambient China aerosols. The three-week high-intensity campaign observed an average E MAC of 2.25 ± 0.55, and sulfates were primary drivers of the enhanced BC absorption. [ABSTRACT FROM AUTHOR]

Urban-like plumes of gases and particulate matter originating from the South Asian region are frequently observed over the Indian Ocean, especially during the dry winter period. However, in addition to the strong sources on mainland South Asia, there are also local Maldivian emissions. The local contributions to the load of fine particulate matter (PM 2.5 ) in the Maldivian capital Malé was assessed using the well-established Maldives Climate Observatory at Hanimaadhoo (MCOH) to represent local background, recording the long-range transported component for a full-year synoptic campaign at both sites in 2013. The year-round levels in both Malé and MCOH are strongly influenced by the seasonality of the monsoon cycle, including precipitation patterns and air-mass transport pathways, with lower levels during the wet summer season. The annual-average PM 2.5 levels in Malé are higher (avg. 19 μg/m 3 ) than at MCOH (avg. 13 μg/m 3 ) with the difference being the largest during the summer, when local emissions play a larger role. The 24-h World Health Organization (WHO) PM 2.5 health guideline was surpassed for the weeklong collections in 71% of the cases in Malé and in 74% of the cases for Hanimaadhoo. This study shows that in the dry/winter season 90 ± 11% of PM 2.5 levels in Malé could be from long-range transport with only 8 ± 11% from local emissions while in the wet/monsoon season the relative contributions are about equal. The concentrations of organic carbon (OC) and elemental carbon (EC) showed similar seasonal patterns as bulk mass PM 2.5 . The relative contribution of total carbonaceous matter to bulk mass PM 2.5 was 17% in Malé and 13% at MCOH, suggesting larger contributions from incomplete combustion practices in the Malé local region. [ABSTRACT FROM AUTHOR]

Abstract: Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line 14C quantification with the chemothermal oxidation method at 375 °C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (f biomass) for fall and winter periods in the range of one-third to half. Large temporal variations in 14C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f biomass appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent 14C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols have severe impacts on climate and health. Most atmospheric BC loadings are now predominantly reported for the PM 2.5 size cut-off. Based on 39 published set of ambient BC concentrations from around the world where PM 2.5 and PM 10 were collected in parallel, we demonstrate that BC in PM 2.5 was only around 80% of that in PM 10. The implication is that around 20% of BC in the global ambient atmosphere is ignored with the now-legacy PM 2.5 sampling approach. Correspondingly, BC of freshly emitted particles from combustion activities is dominantly reported in terms of PM 2.5 , and thus inflicting a bias in the total BC emission inventories. A consequence is that ambient BC is underpredicted when derived from models based on (PM 2.5) emission inventories. This consideration contributes to reconcile existing systematic offset between model predictions and observation-based estimates of climate-relevant effects of anthropogenic BC aerosols. We propose that total ambient BC concentration should be considered rather than the PM 2.5 portion to reduce the uncertainties in estimates of BC effects on the climate. Image 1 • BC concentration in the atmosphere of ambient PM2.5 is 80% of that in PM10. • Ambient PM2.5 underestimated BC concentration in atmosphere. • A gap exists between BC concentration of ambient PM2.5 and of emission inventories. [ABSTRACT FROM AUTHOR]

Black Carbon (BC) deteriorates air quality and contributes to climate warming, yet its regionally- and seasonally-varying emission sources are poorly constrained. Here we employ natural abundance radiocarbon (14C) measurements of BC intercepted at a northern Malaysia regional receptor site, Bachok, to quantify the relative biomass vs. fossil source contributions of atmospheric BC, in a first year-round study for SE Asia (December 2015–December 2016). The annual average 14C signature suggests as large contributions from biomass burning as from fossil fuel combustion. This is similar to findings from analogous measurements at S Asian receptors sites (~50% biomass burning), while E Asia sites are dominated by fossil emission (~20% biomass burning). The 14C-based source fingerprinting of BC in the dry spring season in SE Asia signals an even more elevated biomass burning contribution (~70% or even higher), presumably from forest, shrub and agricultural fires. This is consistent with this period showing also elevated ratio of organic carbon to BC (up from ~5 to 30) and estimates of BC emissions from satellite fire data. Hence, the present study emphasizes the importance of mitigating dry season vegetation fires in SE Asia. Unlabelled Image • We performed a one-year sampling campaign for BC observation in a receptor site of SE Asia. • 14C measurements showed that ~50% of BC was contributed by biomass burning on average during the sampling period. • The contribution of biomass burning in BC significantly increased in the spring season. [ABSTRACT FROM AUTHOR]