COMBUSTION AEROSOL SCAVENGING

As an aerosol ages, the larger particles may scavenge smaller particles in the system. Here we study the scavenging of combustion aerosols by larger particles with a relatively high critical supersaturation. Combustion particles are not composed of pure elemental carbon particles which would be hydrophobic, but rather are composed of mixed soluble and insoluble materials. In this experiment the aerosol's soluble fraction was enhanced through the addition of a small amount of ethyl disulfide to the original fuel. Measurements are made of scavenging rates for the combustion aerosols by the larger particles using the changes which the combustion particles induce in the scavengers when deposition occurs. The presence of the small combustion particle dramatically lowers the critical supersaturation of the composite particle, and this allows the differentiation between the large pure particles and those which have collected a small one. The scavenging is found to occur at faster rates than those predicted by Brownian scavenging theory. The mixed particles resulting from scavenging behave as large inert particles with point activation sites on their surfaces.