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Biomass Burning Leads To Asian Brown Cloud

A study of 14C content in aerosol particles has pinpointed the burning of agricultural residues as a major source of polluted air in the region

by Elizabeth K. Wilson
January 26, 2009 | A version of this story appeared in Volume 87, Issue 4

Credit: © 2009 AAAS/Science
Biomass burning causes much of South Asia's brown haze, as seen in Pune, India.
Credit: © 2009 AAAS/Science
Biomass burning causes much of South Asia's brown haze, as seen in Pune, India.

A radiocarbon study of aerosol particles has pinpointed biomass burning as a major source of the giant brown haze that periodically hovers over large portions of South Asia (Science 2009, 323, 495). This atmospheric brown cloud shows up in the winter and has been attributed to both fossil-fuel and biomass burning. But its sources had not been well characterized, until now. The cloud causes a host of pollution-related health problems in the region and likely impacts climate-related problems, such as glacier melting. Örjan Gustafsson of Stockholm University and colleagues measured carbon isotope ratios of aerosol particles from western India and the Indian Ocean. They found that the particles had higher concentrations of 14C, which is associated with recent plant life. Fossil fuels, by contrast, have much lower concentrations of the isotope. The contributions of carbonaceous aerosol particles from biomass burning, such as agriculture and home-scale wood and cow dung fires, need to be reduced to shrink the cloud, the authors say. Green technologies that limit soot emissions from fires need to be considered in addition to strategies for reducing emissions from automobiles and power plants, they add.


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