Gas-to-particle conversion in photochemical smog: Aerosol growth laws and mechanisms for organics

Abstract

Experiments were conducted to determine particle growth rates as a function of particle size in the presence of reacting organic gases. Hydrocarbons and oxides of nitrogen were added to unfiltered ambient air in an 80 m 3 Teflon bag exposed to natural solar radiation. The ensuing photochemical reactions resulted in growth of the particles originally present. The size distribution of the evolving aerosol was measured in the size range above 0.3 μm using a single particle optical counter. From the change in the size distribution with time, the particle growth rate was determined as a function of size and time. The results could be explained by a mechanism based on diffusion to the particles of condensable gases formed by chemical reaction, with a critical particle size below which growth did not occur (Kelvin effect). A growth law corresponding to this mechanism was used to compute a smog aerosol size distribution which agreed well with atmospheric measurements.