When atmospheric organic aerosols are produced from atmospherically oxidized hydrocarbons, they form particulate oxidizers, including quinones, organic hydroperoxides, and peroxyacyl nitrates (PAN). These particulate oxidizers can modify cellular materials (e.g., proteins and enzymes), and adversely modulate cell functions. In this study, the contribution of particulate oxidizers in secondary organic aerosol (SOA) to the oxidative potential was investigated. SOA were generated from the photooxidation of toluene, 1,3,5-trimethylbenzene, isoprene, and α-pinene under varied NOx levels. Oxidative potential was determined from the typical mass-normalized consumption of dithiothreitol, a surrogate compound. At high NOx conditions, the DTT consumption rate (DTTt at 30 min) of toluene SOA was 2–5 times higher than that of other types of SOA. Isoprene DTTt significantly decreased with increasing NOx (up to 69 % reduction by changing the hydrocarbon/NOx ratio from 30 to 5). The DTTt of 1,3,5-trimethylbenzene and α-pinene SOA was insensitive to NOx under the experimental conditions of this study. The significance of quinones to the oxidative potential of SOA was tested via the enhancement of DTT consumption in the presence of 2,4-dimethylimidazole, a co-catalyst for the redox cycling of quinones; however, no significant effect of 2,4-dimethylimidazole on modulation of DTT consumption was observed for all SOA, suggesting that a negligible amount of quinones was present in SOA of this study. For toluene and isoprene, the total quantities of PAN and organic hydroperoxides were also measured using the Griess assay and the 4-nitrophenylboronic acid assay, respectively. The amount of organic hydroperoxides was substantial, while PAN was found to be insignificant for both SOA. The mass-based DTT consumption (DTTm) of isoprene SOA was almost exclusively attributable to organic hydroperoxides, while toluene DTTm was partially attributable to organic hydroperoxides. The results of the model compound study suggest that electron-deficient alkenes, which are abundant in toluene SOA, could also react with sulfhydryl groups in DTT. The SOA sourced from gasoline SOA yielded the similar amount of orgnic hydroperoxides with toluene SOA but showed higher DTTm than toluene SOA due to the influence by naphthalene-base quinones. The quantity of particulate oxidizers in SOA were also dynamic as SOA aging proceeded.

Dithiothreitol activity by particulate oxidizers in atmospheric organic aerosol

254th National Meeting (2017)

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