| 1. |
- Andersson, August, et al.
(författare)
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Seasonal source variability of carbonaceous aerosols at the Rwanda Climate Observatory
- 2020
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:8, s. 4561-4573
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Tidskriftsartikel (refereegranskat)abstract
- Sub-Saharan Africa (SSA) is a global hot spot for aerosol emissions, which affect the regional climate and air quality. In this paper, we use ground-based observations to address the large uncertainties in the source-resolved emission estimation of carbonaceous aerosols. Ambient fine fraction aerosol was collected on filters at the high-altitude (2590 m a.s.1.) Rwanda Climate Observatory (RCO), a SSA background site, during the dry and wet seasons in 2014 and 2015. The concentrations of both the carbonaceous and inorganic ion components show a strong seasonal cycle, with highly elevated concentrations during the dry season. Source marker ratios, including carbon isotopes, show that the wet and dry seasons have distinct aerosol compositions. The dry season is characterized by elevated amounts of biomass burning products, which approach similar to 95 % for carbonaceous aerosols. An isotopic mass-balance estimate shows that the amount of the carbonaceous aerosol stemming from savanna fires may increase from 0.2 mu g m(-3) in the wet season up to 10 mu g m(-3) during the dry season. Based on these results, we quantitatively show that savanna fire is the key modulator of the seasonal aerosol composition variability at the RCO.
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| 2. |
- Bikkina, Srinivas, et al.
(författare)
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Air quality in megacity Delhi affected by countryside biomass burning
- 2019
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Ingår i: Nature Sustainability. - : Springer Science and Business Media LLC. - 2398-9629. ; 2:3, s. 200-205
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Tidskriftsartikel (refereegranskat)abstract
- South Asian megacities are strong sources of regional air pollution. Delhi is a key hotspot of health-and climate-impacting black carbon (BC) emissions, affecting environmental sustainability in densely populated northern India. Effective mitigation of BC impact is hampered by highly uncertain emission source estimates. Here, we use dual-carbon isotope fingerprints (delta C-13/Delta C-14) of BC to constrain the seasonal source variability in Delhi. These measurements show that lower BC concentrations in summer are predominantly from fossil fuel sources (similar to 83%). However, large-scale open burning of post-harvest crop residue/wood in nearby rural regions is contributing to severe haze pollution in Delhi during winter and autumn (similar to 42 +/- 17%). Hence, the common conception that megacities affect their surroundings is here amended or seasonally reversed. Therefore, to combat the severe air pollution problems in Delhi and the environmental quality of northern India, current urban efforts need to be complemented with countryside regional mitigation.
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| 3. |
- Bikkina, Srinivas, et al.
(författare)
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Carbon isotope-constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo-Gangetic Plain
- 2017
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 122:9, s. 4903-4923
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Tidskriftsartikel (refereegranskat)abstract
- The Indo-Gangetic Plain (IGP) in northern India, Pakistan, and Bangladesh is a major source of carbonaceous aerosols in South Asia. However, poorly constrained seasonality of their sources over the IGP leads to large uncertainty in climate and health effects. Here we present a first data set for year-round radiocarbon (C-14) and stable carbon (C-13)-based source apportionment of total carbon (TC) in ambient PM10 (n = 17) collected from an urban site (Kanpur: 26.5 degrees N, 80.3 degrees E) in the IGP during January 2007 to January 2008. The year-round C-14-based fraction biomass (f(bio-TC)) estimate at Kanpur averages 777% and emphasizes an impact of biomass burning emissions (BBEs). The highest f(bio-TC) (%) is observed in fall season (October-November, 856%) followed by winter (December-February, 804%) and spring (March-May, 758%), while lowest values are found in summer (June-September, 69 +/- 2%). Since biomass/coal combustion and vehicular emissions mostly contribute to carbonaceous aerosols over the IGP, we predict C-13(TC) (C-13(pred)) over Kanpur using known C-13 source signatures and the measured C-14 value of each sample. The seasonal variability of C-13(obs)-C-13(pred) versus C-14(TC) together with air mass back trajectories and Moderate Resolution Imaging Spectroradiometer fire count data reveal that carbonaceous aerosols in winter/fall are significantly influenced by atmospheric aging (downwind transport of crop residue burning/wood combustion emissions in the northern IGP), while local sources (wheat residue combustion/vehicular emissions) dominate in spring/summer. Given the large temporal and seasonal variability in sources and emission strength of TC over the IGP, C-14-based constraints are, thus, crucial for reducing their uncertainties in carbonaceous aerosol budgets in climate models.
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| 4. |
- Bosch, Carme, et al.
(författare)
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Source-diagnostic dual-isotope composition and optical properties of water-soluble organic carbon and elemental carbon in the South Asian outflow intercepted over the Indian Ocean
- 2014
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 119:20, s. 11743-11759
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Tidskriftsartikel (refereegranskat)abstract
- 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 (C-14) data show that WSOC has a significantly higher biomass/biogenic contribution (865%) compared to EC (594%). The more C-13-enriched signature of MCOH-WSOC (-20.80.7) compared to MCOH-EC (-25.8 +/- 0.3 parts per thousand) and megacity Delhi WSOC (-24.1 +/- 0.9 parts per thousand) suggests that WSOC is significantly more affected by aging during long-range transport than EC. The C-13-C-14 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 (MAC(365)) was 0.5 +/- 0.2 m(2)g(-1) 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 similar to 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.
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| 5. |
- Chen, Bing, et al.
(författare)
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Source Forensics of Black Carbon Aerosols from China
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:16, s. 9102-9108
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Tidskriftsartikel (refereegranskat)abstract
- The limited understanding of black carbon (BC) aerosol emissions from incomplete combustion causes a poorly constrained anthropogenic climate warming that globally may be second only to CO2 and regionally, such as over East Asia, the dominant driver of climate change. The relative contribution to atmospheric BC from fossil fuel versus biomass combustion is important to constrain as fossil BC is a stronger climate forcer. The source apportionment is the underpinning for targeted mitigation actions. However, technology-based bottom-up emission inventories are inconclusive, largely due to uncertain BC emission factors from small-scale/household combustion and open burning. We use top-down radiocarbon measurements of atmospheric BC from five sites including three city sites and two regional sites to determine that fossil fuel combustion produces 80 +/- 6% of the BC emitted from China. This source-diagnostic radiocarbon signal in the ambient aerosol over East Asia establishes a much larger role for fossil fuel combustion than suggested by all 15 BC emission inventory models, including one with monthly resolution. Our results suggest that current climate modeling should refine both BC emission strength and consider the stronger radiative absorption associated with fossil-fuel-derived BC. To mitigate near-term climate effects and improve air quality in East Asia, activities such as residential coal combustion and city traffic should be targeted.
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| 6. |
- Kirillova, Elena N., et al.
(författare)
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C-13- and C-14-based study of sources and atmospheric processing of water-soluble organic carbon (WSOC) in South Asian aerosols
- 2013
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Ingår i: Journal of Geophysical Research - Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 118:2, s. 614-626
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble organic carbon (WSOC) is typically a large component of carbonaceous aerosols with a high propensity for inducing cloud formation. The sources of WSOC, which may be both of primary and secondary origins, are in general poorly constrained. This study assesses the concentrations and dual-carbon isotope (14C and 13C) signatures of South Asian WSOC during a 15-month continuous campaign in 2008-2009. Total suspended particulate matter samples were collected at Sinhagad (SINH) India and at the Maldives Climate Observatory at Hanimaadhoo (MCOH). Monsoon-driven meteorology yields significant WSOC concentration differences between the dry winter season (0.94±0.43 μg m-3 MCOH and 3.6±2.3 μg m-3 SINH) and the summer monsoon season (0.10±0.04 μg m-3 MCOH and 0.35±0.21 μg m-3 SINH). Radiocarbon-based source apportionment of WSOC shows the dominance of biogenic/biomass combustion sources but also a substantial anthropogenic fossil-fuel contribution (17±4% MCOH and 23±4% SINH). Aerosols reaching MCOH after long-range over-ocean transport were enriched by 3-4‰ in δ13C-WSOC relative to SINH. This is consistent with particle-phase aging processes influencing the δ13C-WSOC signal in the South Asian regional receptor atmosphere.
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| 7. |
- Kirillova, Elena N., et al.
(författare)
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Natural Abundance C-13 and C-14 Analysis of Water-Soluble Organic Carbon in Atmospheric Aerosols
- 2010
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 82:19, s. 7973-7978
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble organic carbon (WSOC) constitutes a large fraction of climate-forcing organic aerosols in the atmosphere, yet the sources of WSOC are poorly constrained. A method was developed to measure the stable carbon isotope (delta C-13) and radiocarbon (delta C-14) composition of WSOC for apportionment between fossil fuel and different biogenic sources. Synthetic WSOC test substances and ambient aerosols were employed to investigate the effect of both modern and fossil carbon contamination and any method-induced isotope fractionation. The method includes extraction of aerosols collected on quartz filters followed by purification and preparation for off-line delta C-13 and Delta C-14 determination. The preparative freeze-drying step for isotope analysis yielded recoveries of only similar to 70% for ambient aerosols and WSOC probes. However, the delta C-13 of the WSOC isolates were in agreement with the delta C-13 of the unprocessed starting material, even for the volatile oxalic acid probe (6.59 +/- 0.37 parts per thousand vs 6.33 +/- 0.31 parts per thousand; 2 sd). A C-14-fossil phthalic acid WSOC probe returned a fraction modern biomass of <0.008 whereas a C-14-modern sucrose sucrose standard yielded a fraction modern of >0.999, indicating the Delta C-14-WSOC method to be free of both fossil and contemporary carbon contamination. Application of the (delta C-13/Delta C-14-WSOC method to source apportion climate-affecting aerosols was illustrated be constraining that WSOC in ambient Stockholm aerosols were 88% of contemporary biogenic C3 plant origin.
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| 8. |
- Kirillova, Elena N., et al.
(författare)
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Sources and light absorption of water-soluble brown carbon aerosols in the outflow from northern China
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Tidskriftsartikel (refereegranskat)abstract
- High loadings of anthropogenic carbonaceous aerosols in Chinese air influence the air quality for over 1 billion people and impact the regional climate. A large fraction (17 – 80%) of this aerosol carbon is water soluble, promoting cloud formation and thus climate cooling. Recent findings, however, suggest that water-soluble carbonaceous aerosols also absorb sunlight, bringing additional direct and indirect climate warming effects, yet the extent and nature of light absorption by this water-soluble brown carbon (WS-BrC) and its relation to sources is poorly understood. Here, we combine source estimates constrained by dual-carbon-isotope with light absorption measurements of WS-BrC for a March 2011 campaign at the Korea Climate Observatory at Gosan (KCOG), a receptor station in SE Yellow Sea for the outflow from N. China. The mass absorption cross-section (MAC) of WS-BrC for air masses from N. China were in general higher (0.8 – 1.1 m2/g), than from other source regions (0.3 – 0.8 m2/g). We estimate that this effect corresponds to 13 – 49% of the radiative forcing caused by light absorption by black carbon. Radiocarbon constraints show that the WS-Br in Chinese outflow had significantly higher amounts of fossil sources (30 – 50%) compared to previous findings in S. Asia, N. America and Europe. Stable carbon (δ13C) measurements indicated influence of aging during air mass transport. These results indicate the importance of incorporating WS-BrC in climate models and the need to constrain climate effects by emission source sector.
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| 9. |
- Kirillova, Elena N., et al.
(författare)
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Water-soluble organic carbon aerosols during a full New Delhi winter : Isotope-based source apportionment and optical properties
- 2014
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH - ATMOSPHERES. - 2169-8996. ; 119:6, s. 3476-3485
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Tidskriftsartikel (refereegranskat)abstract
- Water soluble organic carbon (WSOC) aerosol is a major constituent (~ 20-80% of the total organic carbon) of the ‘brown cloud’ that shades the Indian Subcontinent. Due to the multiple formation pathways (both primary and secondary), the emissions sources of WSOC are particularly poorly constrained. In this study, we present radiocarbon constraints on the biomass vs fossil sources of WSOC in PM2.5 for the 2010/11 winter period for the megacity Delhi, situated in the center of the heavily polluted Indo-Gangetic Plain. The fossil contribution (22±4%) to WSOC in Delhi is found to be similar to fossil fraction at Indian background sites. Stable carbon analysis shows that Delhi WSOC is more depleted in 13C relative to what is found at receptor sites, indicating that near-source WSOC is less affected by atmospheric aging. In addition, the light absorptive properties of WSOC were investigated. The mass absorption cross section at 365 nm (MAC365) ranged 1.1 – 2.7 m2/g, and the corresponding absorption Ångström exponent (AAE) ranged between 3.1 and 9.3. Using a simplistic estimate of the relative absorptive radiative forcing was found to be 6 – 42 % relative to that of black carbon. Taken together this near-source study emphasize the importance of taking into account the complex transformations of WSOC during air mass transport, as compared with regional receptor sites.
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