The predicted behavior of the size- and chemical-composition distribution of airborne particles in the Los Angeles area is examined as it changes in response to specific emissions control strategies. Model calculations indicate that strategiescurrently envisioned to control the emissions of primary particles in the Los Angeles area effectively reduce the atmospheric concentrations of particles between 0.1-0.3μm particle diameter and above 2.5μm particle diameter but do little to reduceparticulate concentrations between 0.6 and 0.8μm particle diameter. Analysis reveals that in Los Angeles, most atmospheric particles with diameters between 0.6-0.8μm begin as water-soluble nonsea salt background particles over the Pacific Ocean whichthen are transformed by significant accumulation of gas-to-particle conversion products as they are advected across the urban area. Control of primary particulate emissions alone does not reduce the amount of secondary aerosol which forms in theatmosphere and may even serve to redistribute this secondary material to particles with diameters that scatter light more efficiently. Strategies originally designed to reduce ambient ozone concentrations through the control of emissions of reactiveorganic gases (ROG) and oxides of nitrogen (NO{sub}x) would reduce fine particle mass concentrations at Claremont CA on August 28, 1987 by 9.5 under the conditions studied here, primarily by reducing aerosol nitrate concentrations. Additional controls on ammonia emissions would suppress aerosol nitrate formation further. The simultaneous use of all gas-phase and particle-phase emissions control measures studied here would reduce atmospheric particle concentrations by 46 at Claremont, CA, relative to thebase case 1987 summer conditions.
展开▼
