Modeling urban and regional aerosols near acid neutrality—application to the 24–25 June scaqs episode

Mathematically predicting the size and composition distribution of atmospheric aerosols can help to elucidate the complex link between emissions and particulate air quality. Wexler et al. (1994) identified and analyzed the atmospheric aerosol processes and estimated the relative importance of each term using parameters typical in South Coast Air Basin (SoCAB). The result was a general dynamic equation including only the relevant terms. In a previous paper we described practical difficulties integrating these equations under the acid-neutral conditions common in the SoCAB and introduced an acid equilibrium assumption, that is, the aerosol hydrogen ion concentration can be assumed to be in equilibrium with the gas-phase acidity. In this paper we use the model to predict the size and composition distribution of PM during the 24–25 June 1987 SCAQS episode. The predicted size distribution is compared to the SCAQS measurement data by John et al. (1989a); John et al. (1989b) and John et al. (1990).