Laboratory studies of the impact of aerosol composition on the heterogeneous oxidation of 1-propanol

The effects of (NH4)2SO4, NH4NO3, NaCl, NH4Cl, and Na2SO4 aerosols on the kinetics of 1-propanol oxidation in the presence of the hydroxyl radical have been investigated using the relative rate technique. p-Xylene was used as a reference compound. Two different aerosol concentrations that are typical of polluted urban conditions were tested. The total surface areas of aerosols were 1400 (condition I) and 3400 μm2 cm−3 (condition II). Results indicate that aerosols promote the oxidation of 1-propanol, and the extents of the promoting effects depend on the aerosol composition and concentration. Increases in the relative rates of the 1-propanol/√OH reaction vs. the p-xylene/√OH reaction were only observed for (NH4)2SO4 aerosol conditions I and II, NH4NO3 aerosol condition II, and NH4Cl aerosol condition II. These results indicate that NH4+ is the species promoting the oxidation of 1-propanol, and suggests the possibility of a strong interaction between NH4+ and 1-propanol that can change the activation energy of the initial √OH attack. These results have profound implications on the use of air quality models for the assessment of air pollution control strategies.