Investigations of gas-to-particle conversion in the atmosphere

Continental aerosol particle size distributions were measured as a function of time at the background station Aisetas and in the suburb of Vilnius. Marine aerosol particle formation was studied in outdoor photochemical chamber experiments performed on the coast of the Baltic sea. The functional dependence of the particle diameter growth rate on the particle size was calculated from the aerosol particle size distribution data and was compared with the theoretical predictions for the particle growth due to vapor condensation or due to the adsorption of aerosol precursor gases on the particle surface or within an airborne droplet. It was shown that during summer months condensation of low pressure vapors formed by gas phase homogeneous chemical reactions was predominant mechanism of the continental aerosol particle growth. While in winter growth of a submicrometer continental aerosol particle was frequently governed by two competing processes: condensation of low pressure vapors and heterogeneous oxidation of aerosol precursor gases inside the liquid droplet. Ozone was found to be an active oxidant in the heterogeneous aqueous phase chemical reactions. The outdoor photochemical chamber experiments showed that aqueous phase chemical reactions were responsible for the formation of marine sulfuric acid aerosol particles from the dimethylsulfide. After these particles were partially neutralized by ammonia to the ammonium sulfate or bisulfate, their further growth was observed to be surface limited.