Air Quality
10/3/2009 1:49:36 PM EST
Researchers identify new pathway for the formation of light-scattering haze from plant emissions
Partner, Ropers Majeski Kohn & Bentley
Prior posts have noted the volatiles from trees and plants are in fact a not insignificant contributor to smog formation. A new study now shows natural hydrocarbon emissions contribute to light-scattering aerosols [http://en.wikipedia.org/wiki/Aerosols]that contribute to haze and influence climate; aerosols influence how much sunlight reaches the Earth’s surface and how much is scattered back into space. Climate simulations will benefit from an understanding of these processes.
Sources of aerosols include volcanoes, byproducts of fossil fuel combustion, and sea spray. Worldwide, plants release more than 550 million metric tons of the hydrocarbon isoprene [http://en.wikipedia.org/wiki/Isoprene] into the atmosphere each year. But scientists have disagreed about the particular chain of chemical reactions that transform isoprene into haze-forming aerosols. A new study now demonstrates a potential mechanism.
Researchers created dihydroxyepoxides by placing isoprene and hydrogen peroxide in an 800-liter bag of unpolluted air and then illuminating the mix with ultraviolet light. The UV light stimulated chemical reactions, just as sunlight would, and the hydrogen peroxide served as a source of hydroxyl radicals (highly reactive compounds sometimes referred to as “the detergent of the atmosphere”). Isoprene and hydroxyl radicals reacted to form dihydroxyepoxides by two separate chemical processes. Because the resulting epoxides [http://en.wikipedia.org/wiki/Epoxides] are highly soluble, they readily dissolve into droplets of moisture in the air to form organic-rich aerosols. The researchers note that this process could be a major source of atmospheric aerosols. The work also helps to explain the high level of aerosols found in the tropics.
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