Effect of emissions control strategies on the size and composition distribution of urban particulate air pollution

The predicted behavior of the size- and chemical-composition distribution o f airborne particles in the Los Angeles area is examined as it changes in r esponse to specific emissions control strategies. Model calculations indica te that strategies currently envisioned to control the emissions of primary particles in the Los Angeles area effectively reduce the atmospheric conce ntrations of particles between 0.1-0.3 mu m particle diameter and above 2.5 mu m particle diameter but do little to reduce particulate concentrations between 0.6 and 0.8 mu m particle diameter. Analysis reveals that in Los An geles, most atmospheric particles with diameters between 0.6-0.8 mu m begin as water-soluble nonsea salt background particles over the Pacific Ocean w hich then are transformed by significant accumulation of gas-to-particle co nversion products as they are advected across the urban area. Control of pr imary particulate emissions alone does not reduce the amount of secondary a erosol which forms in the atmosphere and may even serve to redistribute thi s secondary material to particles with diameters that scatter light more ef ficiently Strategies originally designed to reduce ambient ozone concentrat ions through the control of emissions of reactive organic gases (ROG) and o xides of nitrogen (NOx) would reduce fine particle mass concentrations at C laremont CA on August 28, 1987 by 9.5% under the conditions studied here, p rimarily by reducing aerosol nitrate concentrations. Additional controls on ammonia emissions would suppress aerosol nitrate formation further. The si multaneous use of all gas-phase and particle-phase emissions control measur es studied here would reduce atmospheric particle concentrations by 46% at Claremont, CA, relative to the base case 1987 summer conditions.