Atmospheric oxidation of isoprene and 1,3-butadiene: influence of aerosol acidity and relative humidity on secondary organic aerosol

摘要

The effects of acidic seed aerosols on the formation of secondary organicaerosol (SOA) have been examined in a number of previous studies, several ofwhich have observed strong linear correlations between the aerosol acidity(measured as nmol H m air sample volume) and the percent changein secondary organic carbon (SOC). The measurements have used severalprecursor compounds representative of different classes of biogenichydrocarbons including isoprene, monoterpenes, and sesquiterpenes. To date,isoprene has displayed the most pronounced increase in SOC, although fewmeasurements have been conducted with anthropogenic hydrocarbons. In thepresent study, we examine several aspects of the effect of aerosol acidity onthe secondary organic carbon formation from the photooxidation of1,3-butadiene, and extend the previous analysis of isoprene.The photooxidation products measured in the absence and presence of acidicsulfate aerosols were generated either through photochemical oxidation ofSO or by nebulizing mixtures of ammonium sulfate and sulfuric acid intoa 14.5 m smog chamber system. The results showed that, like isopreneand β-caryophyllene, 1,3-butadiene SOC yields linearly correlate withincreasing acidic sulfate aerosol. The observed acid sensitivity of0.11% SOC increase per nmol m increase in H wasapproximately a factor of 3 less than that measured for isoprene. The resultsalso showed that the aerosol yield decreased with increasing humidity forboth isoprene and 1,3-butadiene, although to different degrees. Increasingthe absolute humidity from 2 to 12 g m reduced the 1,3-butadieneyield by 45% and the isoprene yield by 85%.