GROWTH LAWS FOR ATMOSPHERIC AEROSOL-PARTICLES - AN EXAMINATION OF THEBIMODALITY OF THE ACCUMULATION-MODE

The growth of atmospheric aerosol particles was examined by first deri ving growth laws and their corresponding time scales for all the impor tant aerosol processes: condensation, coagulation, aqueous-phase react ions in droplets or aerosol particles, and reactions taking place at t he interface of two phases. These tools were then used to explore and explain the frequently observed splitting of the accumulation mode int o two individual modes. Two environments-the remote marine boundary la yer and the South Coast Air Basin of Los Angeles (SoCAB)-were consider ed. Our analysis points out that the observed mode separation cannot r esult from condensational or coagulational growth. In both the marine boundary layer and the SoCAB, H2O2/O-3 sulfate formation in droplets d uring clouds or fogs provides all the features required for explaining the bimodality. In the SoCAB, this process may be assisted or even do minated by the trace metal catalyzed droplet-phase SO2 oxidation.