Computer models of air quality provide local governments with the scientific information they use to regulate air pollution emissions -- but these models are not always as accurate as regulators would like.

Researchers at the U.S. Department of Energy's Ernest Orlando Lawrence Berkeley National Laboratory and the University of California at Berkeley have been studying the photochemical characteristics of air pollution in southern California as part of an effort funded by the California Air Resources Board (CARB) to improve the reliability of air quality models. The Berkeley Lab team's work has yielded new insights into how variability in the solar flux and the concentration of aerosols in the atmosphere affect the formation of smog.

Since the passage of the Clean Air Act in 1990, computer-based air quality models have been the basis of air quality regulation in the United States. Reducing uncertainties in model results has been a focus of much research. "One of the uncertainties," says Berkeley Lab's Laurent Vuilleumier, "is how well the models represent the optical properties of the atmosphere and their effect on the photochemical reactions that form smog." CARB designated variability in sunlight and its effect on photochemistry as one of the areas needing improvement in current air quality models.

Vuilleumier, a scientist in the Lab's Environmental Energy Technologies Division, UC Berkeley's Rob Harley, EETD's Nancy Brown, and colleagues have been using data from CARB's 1997 Southern California Ozone Study to gain a better understanding of the relationship between the amount of light entering the atmosphere and the rates of photochemical reactions that form ozone, a significant component of smog that influences the concentrations of other air pollutants.

"Ozone concentration is extremely sensitive to reactions that are driven by sunlight," explains Vuilleumier. "These photolysis reactions initiate the decomposition of chemical species such as nitr
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Contact: Allan Chen
A_Chen@lbl.gov
510-486-4210
DOE/Lawrence Berkeley National Laboratory
5-Feb-2001