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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 16 | Copyright
Atmos. Chem. Phys., 17, 9965-9977, 2017
https://doi.org/10.5194/acp-17-9965-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Aug 2017

Research article | 25 Aug 2017

Dithiothreitol activity by particulate oxidizers of SOA produced from photooxidation of hydrocarbons under varied NOx levels

Huanhuan Jiang, Myoseon Jang, and Zechen Yu Huanhuan Jiang et al.
  • Department of Environmental Engineering Sciences, Engineering School of Sustainable Infrastructure and Environment, University of Florida, Gainesville, FL 32608, USA

Abstract. When hydrocarbons (HCs) are atmospherically oxidized, they form particulate oxidizers, including quinones, organic hydroperoxides, and peroxyacyl nitrates (PANs). 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 aerosols (SOAs) to the oxidative potential was investigated. SOAs 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 rate (reaction time t = 30min) of dithiothreitol (DTTt), a surrogate for biological reducing agents. Under high-NOx conditions, the DTTt of toluene SOA was 2–5 times higher than that of the other types of SOA. Isoprene DTTt significantly decreased with increasing NOx (up to 69% reduction by changing the HCNOx 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 through 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 the SOA of this study. For toluene and isoprene, mass-normalized DTT consumption (DTTm) was determined over an extended period of reaction time (t = 2h) to quantify their maximum capacity to consume DTT. The total quantities of PANs and organic hydroperoxides in toluene SOA and isoprene SOA were also measured using the Griess assay and the 4-nitrophenylboronic acid assay, respectively. Under the NOx conditions (HCNOx ratio: 5–36ppbCppb−1) applied in this study, the amount of organic hydroperoxides was substantial, while PANs were found to be insignificant for both SOAs. Isoprene DTTm was almost exclusively attributable to organic hydroperoxides, while toluene DTTm was partially attributable to organic hydroperoxides. The DTT assay results of the model compound study suggested that electron-deficient alkenes, which are abundant in toluene SOA, could also modulate DTTm.

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The oxidative potential of secondary organic aerosol (SOA) was measured by dithiothreitol assay. To quantify the reactive functional groups of particulate oxidizers that can increase dithiothreitol response, the quantities of quinones, organic hydroperoxides, and peroxy acyl nitrates were measured by chemical assays. Organic hydroperoxides were largely attributed to the oxidative potential of SOA. The results provide a deep understanding of the mechanistic role of SOA in modifying biomolecules.
The oxidative potential of secondary organic aerosol (SOA) was measured by dithiothreitol assay....
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