Effects of anthropogenic aerosol particles on California and South Coast climate

This study examines the effects of anthropogenic aerosol particles and their precursor gases (AAPPG) on precipitation, winds, temperatures, cloud optical depth, cloud fraction, and other parameters in California and California's South Coast Air Basin. Nested global-through-urban scale model simulations were run for February and August 1999. The model treated discretized size- and composition-resolved precipitation, clouds, and aerosol particles and their feedbacks to meteorology and radiation. Three nested grids were treated in each case: a global grid, a California grid, and a South Coast Air Basin grid. The study found that AAPPG decreased overall and upslope-mountain precipitation, increased cloud optical depth, cloud liquid water, and cloud fraction, increased water vapor, decreased surface solar and ultraviolet radiation, increased downward thermal-infrared radiation, decreased ground temperature, slightly increased summer and decreased winter polluted-air temperature, increased boundary-layer stability, decrease mixing depth, and decreased near-surface wind speeds. These results demonstrate by modeled cause and effect some previous measurement/correlation-study findings on the effects of aerosol particles on precipitation but also provide new insight on the effects of aerosol particles on winds and wind energy.