Dithiothreitol activity by particulate oxidizers of SOA produced from photooxidation of hydrocarbons under varied NO<sub><i>x</i></sub> levels
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...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/9965/2017/acp-17-9965-2017.pdf |
| Summary: | 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 <i>α</i>-pinene under varied NO<sub><i>x</i></sub>
levels. Oxidative potential was determined from the typical mass-normalized
consumption rate (reaction time <i>t</i> = 30 min) of dithiothreitol (DTT<sub>t</sub>),
a surrogate for biological reducing agents. Under high-NO<sub><i>x</i></sub> conditions, the
DTT<sub>t</sub> of toluene SOA was 2–5 times higher than that of the other types
of SOA. Isoprene DTT<sub>t</sub> significantly decreased with increasing NO<sub><i>x</i></sub>
(up to 69 % reduction by changing the HC ∕ NO<sub><i>x</i></sub> ratio from 30
to 5). The DTT<sub>t</sub> of 1,3,5-trimethylbenzene and <i>α</i>-pinene SOA was
insensitive to NO<sub><i>x</i></sub> 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 (DTT<sub>m</sub>) was determined over an
extended period of reaction time (<i>t</i> = 2 h) 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
NO<sub><i>x</i></sub> conditions (HC ∕ NO<sub><i>x</i></sub> ratio: 5–36 ppbC ppb<sup>−1</sup>) applied in this study,
the amount of organic hydroperoxides was substantial, while PANs were found
to be insignificant for both SOAs. Isoprene DTT<sub>m</sub> was almost exclusively
attributable to organic hydroperoxides, while toluene DTT<sub>m</sub> 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 DTT<sub>m</sub>. |
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| ISSN: | 1680-7316 1680-7324 |