The Impact of Aerosols on Solar Ultra Violet Radiation and Photochemical Smog

The Impact of Aerosols on Solar Ultraviolet Radiation and Photochemical Smog

R. R. Dickerson*, S. Kondragunta, G. Stenchikov, K. L. Civerolo, B. G. Doddridge, B. N. Holben
ABSTRACT
Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth 's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.

ABSTRACT
Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth 's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.

More than 100 counties in the United States regularly violate the Environmental Protection Agency 's (EPA) Ambient Air Quality Standard for ozone (O3) of 120 ppbv (parts per 109 by volume averaged over 1 hour) (1). This ozone results from the interaction of pollutant oxides of nitrogen and nonmethane hydrocarbons (NMHCs) with solar radiation, for example, via reactions (1) to (4), and is thus sometimes called

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