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Water-soluble organic carbon aerosols during a full New Delhi winter:  Isotope-based source apportionment and optical properties
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
(Indian Institute of Tropical Meteorology, New Delhi, India)
(Indian Institute of Tropical Meteorology, New Delhi, India)
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Number of Authors: 6
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.

Place, publisher, year, edition, pages
2014. Vol. 119, no 6, 3476-3485 p.
Keyword [en]
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: urn:nbn:se:su:diva-89179DOI: 10.1002/2013JD020041ISI: 000336046600045OAI: oai:DiVA.org:su-89179DiVA: diva2:616327
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
In thesis
1. Dual isotope (13C-14C) Studies of Water-Soluble Organic Carbon (WSOC) Aerosols in South and East Asia
Open this publication in new window or tab >>Dual isotope (13C-14C) Studies of Water-Soluble Organic Carbon (WSOC) Aerosols in South and East Asia
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
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:nbn:se:su:diva-89161 (URN)978-91-7447-696-5 (ISBN)
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

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