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Dual isotope (13C-14C) Studies of Water-Soluble Organic Carbon (WSOC) Aerosols in South and East Asia
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atmospheric aerosols may be emitted directly as particles (primary) or formed from gaseous precursors (secondary) from different natural and anthropogenic sources. The highly populated South and East Asia regions are currently in a phase of rapid economic growth to which high emissions of carbonaceous aerosols are coupled. This leads to generally poor air quality and a substantial impact of anthropogenic aerosols on the regional climate. However, the emissions of different carbon aerosol components are still poorly constrained. Water-soluble organic carbon (WSOC) is a large (20-80%) component of carbonaceous aerosols that can absorb solar light and enhance cloud formation, influencing both the direct and indirect climate effects of the aerosols.

A novel method for carbon isotope-based studies, including source apportionment, of the WSOC component of ambient aerosols was developed and tested for recovery efficiency and the risk of contamination using both synthetic test substances and ambient aerosols (paper I). The application of this method for the source apportionment of aerosols in South and East Asia shows that fossil fuel input to WSOC is significant in both South Asia (about 17-23%) highly impacted by biomass combustion practices and in East Asia (up to 50%) dominated by fossil energy sources (papers II, III, IV). Fossil fraction in WSOC in the outflow from northern China is considerably larger than what has been measured in South Asia, Europe and USA (paper IV). A trend of enrichment in heavy stable carbon isotopes in WSOC with distance the particles have been transported from the source is observed in the South Asian region (papers II, III). Dual-isotope (Δ14C and δ13C) analysis demonstrates that WSOC is highly influenced by atmospheric aging processes.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm Univeristy , 2013. , 37 p.
Keyword [en]
atmospheric aerosols, water-soluble organic carbon, carbon isotopes, South Asia, East Asia, source apportionment, aerosol aging
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-89161ISBN: 978-91-7447-696-5 (print)OAI: oai:DiVA.org:su-89161DiVA: diva2:616328
Public defence
2013-05-30, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted.

Available from: 2013-05-08 Created: 2013-04-15 Last updated: 2013-04-16Bibliographically approved
List of papers
1. Natural Abundance C-13 and C-14 Analysis of Water-Soluble Organic Carbon in Atmospheric Aerosols
Open this publication in new window or tab >>Natural Abundance C-13 and C-14 Analysis of Water-Soluble Organic Carbon in Atmospheric Aerosols
2010 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 82, no 19, 7973-7978 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-51746 (URN)10.1021/ac1014436 (DOI)000282257400017 ()
Note
authorCount :4Available from: 2011-01-12 Created: 2011-01-12 Last updated: 2017-12-11Bibliographically approved
2. C-13- and C-14-based study of sources and atmospheric processing of water-soluble organic carbon (WSOC) in South Asian aerosols
Open this publication in new window or tab >>C-13- and C-14-based study of sources and atmospheric processing of water-soluble organic carbon (WSOC) in South Asian aerosols
Show others...
2013 (English)In: Journal of Geophysical Research - Oceans and Atmospheres, ISSN 0148-022A, Vol. 118, no 2, 614-626 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
water-soluble organic carbon, India, biomass burning, aerosol aging
National Category
Environmental Sciences
Research subject
Applied Environmental Science; Atmospheric Sciences; Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-89172 (URN)10.1002/jgrd.50130 (DOI)000317838100027 ()
Funder
Formas, 214-2009-970Knut and Alice Wallenberg Foundation
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2017-12-06Bibliographically approved
3. Water-soluble organic carbon aerosols during a full New Delhi winter:  Isotope-based source apportionment and optical properties
Open this publication in new window or tab >>Water-soluble organic carbon aerosols during a full New Delhi winter:  Isotope-based source apportionment and optical properties
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2014 (English)In: JOURNAL OF GEOPHYSICAL RESEARCH - ATMOSPHERES, ISSN 2169-8996, Vol. 119, no 6, 3476-3485 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
water soluble organic carbon, New Delhi, carbon isotopes, source apportionment, light absorption properties, aerosol aging
National Category
Environmental Sciences Analytical Chemistry
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-89179 (URN)10.1002/2013JD020041 (DOI)000336046600045 ()
Funder
Sida - Swedish International Development Cooperation Agency, AKT-2010-038Formas, 214-2009-970Knut and Alice Wallenberg Foundation
Available from: 2013-04-16 Created: 2013-04-15 Last updated: 2014-07-01Bibliographically approved
4. Sources and light absorption of water-soluble brown carbon aerosols in the outflow from northern China
Open this publication in new window or tab >>Sources and light absorption of water-soluble brown carbon aerosols in the outflow from northern China
Show others...
(English)Article in journal (Refereed) Submitted
Abstract [en]

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.

Keyword
water-soluble organic carbon, carbon isotopes, source apportionment, light absorption properties, aerosol aging, China
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-89189 (URN)
Available from: 2013-04-16 Created: 2013-04-16 Last updated: 2013-04-16Bibliographically approved

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