Effects of ammonium sulfate aerosols on the gas-phase reactions of the hydroxyl radical with organic compounds

Abstract

Air quality modeling is of seminal importance to the assessment of air pollution control strategies. Traditionally, these models include four basic components: meteorology data, emissions data, transport mechanisms, and chemistry. The gas-phase chemistry portions have been based on kinetic and product laboratory studies in relatively pristine gas-phase environments. However, given the abundance of particles in the atmosphere, it is possible that aerosols can have catalytic effects on gas-phase reaction kinetics. These studies focus on elucidating those effects. Ultimately, the data gained can be used to improve regional air quality models. Relative rate studies of the OH radical initiated reactions of n-hexane, p-xylene, and 1-propanol were conducted in a Tedlar bag in the presence of ammonium sulfate aerosols. Results show that ammonium sulfate aerosols promote the reaction of 1-propanol with OH radicals compared to the reactions of n-hexane with OH radicals and p-xylene with OH radicals. The relative rate of the 1-propanol/·OH reaction versus the n-hexane/·OH reaction increased from 0.85±0.05 in the absence of (NH 4) 2SO 4 aerosols to 1.07±0.05 in the presence of aerosols. Also, the relative rate of the 1-propanol/·OH reaction versus the p-xylene/·OH reaction increased from 0.45±0.03 in the absence of (NH 4) 2SO 4 aerosols to 0.56±0.02 in the presence of aerosols.