A 3D Eulerian source-oriented model for an externally mixed aerosol.

A 3D Eulerian source-oriented model for an externally mixed aerosol is developed and then used to compute the contribution that different emission sources make to regional fine particle concentrations in the South Coast Air Basin surrounding Los Angeles, CA, on September 25, 1996. The model simultaneously tracks fine particle concentrations (PM2.5), inhalable particle concentrations (PM10), ozone, and other gaseous pollutant concentrations yielding a tool that can be used to study the control of all of the regulated contaminants in the atmosphere within a single unified framework. Model predictions identify geographical areas that are influenced by PM2.5 associated with crustal material other than paved road dust, paved road dust, diesel engines, food cooking, noncatalyst equipped gasoline engines, catalyst-equipped gasoline engines, combustion of high sulfur-content fuel, other primary particle sources, sea salt, and marine background sulfate particles. The contribution that each of these source types makes to regional fine particle concentrations is distinct, reflecting the unique chemical composition, spatial distribution, and diurnal trends of primary emissions. The single largest contribution to regional PM2.5 in the South Coast Air Basin surrounding Los Angeles is associated with the accumulation of secondary ammonium nitrate on background marine sulfate particles. This pattern indicates that control of PM2.5 concentrations in Los Angeles must be accomplished through a program that includes both reductions in the emissions of gaseous precursors of secondary PM2.5 as well as control of primary particle emissions.