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When hydrocarbons (HCs) are atmospherically oxidized, they formparticulate oxidizers, including quinones, organic hydroperoxides, andperoxyacyl nitrates (PANs). These particulate oxidizers can modify cellularmaterials (e.g., proteins and enzymes) and adversely modulate cellfunctions. In this study, the contribution of particulate oxidizers insecondary 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 NOxlevels. Oxidative potential was determined from the typical mass-normalizedconsumption rate (reaction time t =  30 min) of dithiothreitol (DTTt),a surrogate for biological reducing agents. Under high-NOx conditions, theDTTt of toluene SOA was 2–5 times higher than that of the other typesof SOA. Isoprene DTTt significantly decreased with increasing NOx(up to 69 % reduction by changing the HC ∕ NOx ratio from 30to 5). The DTTt of 1,3,5-trimethylbenzene and α-pinene SOA wasinsensitive to NOx under the experimental conditions of this study. Thesignificance of quinones to the oxidative potential of SOA was tested throughthe enhancement of DTT consumption in the presence of2,4-dimethylimidazole, a co-catalyst for the redox cycling of quinones;however, no significant effect of 2,4-dimethylimidazole on modulation ofDTT consumption was observed for all SOA, suggesting that a negligibleamount of quinones was present in the SOA of this study. For toluene andisoprene, mass-normalized DTT consumption (DTTm) was determined over anextended period of reaction time (t =  2 h) to quantify their maximumcapacity to consume DTT. The total quantities of PANs and organichydroperoxides in toluene SOA and isoprene SOA were also measured using theGriess assay and the 4-nitrophenylboronic acid assay, respectively. Under theNOx conditions (HC ∕ NOx ratio: 5–36 ppbC ppb−1) applied in this study,the amount of organic hydroperoxides was substantial, while PANs were foundto be insignificant for both SOAs. Isoprene DTTm was almost exclusivelyattributable to organic hydroperoxides, while toluene DTTm was partiallyattributable to organic hydroperoxides. The DTT assay results of the modelcompound study suggested that electron-deficient alkenes, which are abundantin toluene SOA, could also modulate DTTm

atmospheric chemistry and physics

Dithiothreitol activity by particulate oxidizers of SOA produced from photooxidation of hydrocarbons under varied NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; levels