Rising air pollution worsens drought, flooding, UMD-led study shows

http://www.eurekalert.org/pub_releases/2011-11/uom-rap110911.php

Public release date: 13-Nov-2011
Contact: Lee Tune
University of Maryland

COLLEGE PARK, Md. – Increases in air pollution and other particulate matter in the atmosphere can strongly affect cloud development in ways that reduce precipitation in dry regions or seasons, while increasing rain, snowfall and the intensity of severe storms in wet regions or seasons, says a new study by a University of Maryland-led team of researchers.

The research provides the first clear evidence of how aerosols -- soot, dust and other small particles in the atmosphere -- can affect weather and climate; and the findings have important economic and water resource implications for regions across the United States and around the world, say the researchers and other scientists.

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Aerosols are tiny solid particles or liquid particles suspended in air. They include soot, dust and sulfate particles, and are what we commonly think of when we talk about air pollution. Aerosols come, for example, from the combustion of fossil fuels, industrial and agricultural processes, and the accidental or deliberate burning of fields and forests. They can be hazardous to both human health and the environment.

Aerosol particles also affect the Earth's surface temperature by either reflecting light back into space, thus reducing solar radiation at Earth's surface, or absorbing solar radiation, thus heating the atmosphere. This variable cooling and heating is, in part, how aerosols modify atmospheric stability that dictates atmospheric vertical motion and cloud formation. Aerosols also affect cloud microphysics because the serve as nuclei around which water droplets or ice particles form. Both processes can affect cloud properties and rainfall. Different processes may work in harmony or offset each other, leading to a complex yet inconclusive interpretation of their long-term net effect.

Greenhouse gases and aerosol particles are two major agents dictating climate change. The mechanisms of climate warming impacts of increased greenhouse gases are clear (they prevent solar energy that has been absorbed by the earth's surface from being radiated as heat back into space), but the climate effects of increased aerosols are much less certain. Until now, studies of the long-term effects of aerosols on climate change have been largely lacking and inconclusive because their mechanisms are much more sophisticated, variable, and tangled with meteorology.

"This study demonstrates the importance and value of keeping a long record of continuous and comprehensive measurements such as the highly instrumented (ARM) sites run by the Department of Energy's Office of Science, including the Southern Great Plains site, to identify and quantify important roles of aerosols in climate processes," says Stephen E. Schwartz, a scientist at Brookhaven National Laboratory. "While the mechanisms for some of these effects remain uncertain, the well-defined relationships discovered here clearly demonstrate the significance of the effects. Developing this understanding to represent the controlling processes in models remains a future challenge, but this study clearly points in important directions."

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