Effects of temperature on wood soot pah decay in atmospheres with sunlight and low NO x

Abstract

Wood smoke particles were exposed to midday sunlight in outdoor Teflon film chambers. Chamber NO 2 concentrations were limited to 0.03 ppm, and less than 0.01 ppm of photochemically generated ozone was produced. The overall initial rate of PAH decay on soot particles could be approximated by a first order rate expression. At moderate temperatures (~ 20°C) the rate of PAH decay on soot particles was appreciable with atmospheric half-lives of individual PAH in the range of 30–60 min. At temperatures of −7°C the rates of decay were substantially slower with half-lives that extended to many hours if not days. When outdoor temperatures changed from 20°C to −7°C the rate of decay of six different PAH decreased by a factor of four to ten. These experiments strongly suggest that the magnitude of PAH decay on soot particles due to photo-induced processes can be strongly influenced by temperature.