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Science 23 January 2009:
Vol. 323. no. 5913, pp. 495 - 498
DOI: 10.1126/science.1164857
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Reports

Brown Clouds over South Asia: Biomass or Fossil Fuel Combustion?

Örjan Gustafsson,1* Martin Kruså,1 Zdenek Zencak,1 Rebecca J. Sheesley,1 Lennart Granat,2 Erik Engström,2 P. S. Praveen,3 P. S. P. Rao,4 Caroline Leck,2 Henning Rodhe2

Carbonaceous aerosols cause strong atmospheric heating and large surface cooling that is as important to South Asian climate forcing as greenhouse gases, yet the aerosol sources are poorly understood. Emission inventory models suggest that biofuel burning accounts for 50 to 90% of emissions, whereas the elemental composition of ambient aerosols points to fossil fuel combustion. We used radiocarbon measurements of winter monsoon aerosols from western India and the Indian Ocean to determine that biomass combustion produced two-thirds of the bulk carbonaceous aerosols, as well as one-half and two-thirds of two black carbon subfractions, respectively. These constraints show that both biomass combustion (such as residential cooking and agricultural burning) and fossil fuel combustion should be targeted to mitigate climate effects and improve air quality.

1 Department of Applied Environmental Science, Stockholm University, 10691 Stockholm, Sweden.
2 Department of Meteorology, Stockholm University, 10691 Stockholm, Sweden.
3 Maldives Climate Observatory at Hanimaadhoo (MCOH), Republic of the Maldives.
4 Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune 411 008, India.

* To whom correspondence should be addressed. E-mail: orjan.gustafsson{at}itm.su.se

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Science. ISSN 0036-8075 (print), 1095-9203 (online)