The rate of neutralization of sulfuric acid aerosol by ammonia gas has been measured in a laboratory flow reactor for particle diameters between 0.3 and 1.4 μm and for relative humidities between 8 and 80%. The rates were between 21 and 70% of the rates expected if diffusion of NH3 to the aerosol droplets was the rate-determining factor, and the reaction coefficient, which is the fraction of gas-particle collisions resulting in a chemical reaction, increased with increasing particle size. A simple model of H2SO4 aerosol generation and neutralization in the atmosphere showed that sulfate aerosol more acidic than NH4HSO4 should only be present during periods of rapid oxidation of the precursor SO2 and high ratios of [SO2] to [NH3] or when the equilibrium vapor pressure of NH3 over the partially neutralized H2SO4 droplet exceeds the ambient NH3 partial pressure.
ASJC Scopus subject areas
- Environmental Chemistry