Department of Chemistry, University of Toronto, Toronto, ON, Canada.
Environ Sci Technol. 2011 Mar 15;45(6):2131-6. doi: 10.1021/es102874d. Epub 2011 Feb 22.
The effect of oxidation on the redox-cycling activity of engine exhaust particles is examined. Particles obtained from a two-stroke gasoline engine were oxidized in a flow tube with ozone on a one-minute time scale both in the presence and absence of substantial gas-phase exhaust components. Whereas ozone concentrations were high, the ozone exposures were approximately equivalent to 60 ppb ozone for 2-8 h. Oxidation led to substantial increases in redox-cycling of aqueous extracts of filtered particles, as measured using the dithiothreitol (DTT) assay. Increases in redox activity when the entire exhaust was oxidized were primarily driven by deposition of redox-active secondary organic aerosol (SOA), resulting in an upper-limit DTT activity of 8.6 ± 2.0 pmol DTT consumed per min per microgram of particles, compared to 0.73 ± 0.60 pmol min(-1) μg(-1) for fresh, unoxidized exhaust particles. Redox-cycling activity reached higher levels when VOC denuded exhaust was oxidized, with the highest DTT activity observed being 16.7 ± 1.6 pmol min(-1) μg(-1) with no upper limit reached for the range of ozone exposures used in this study. Our results provide laboratory support for the hypothesis that the toxicity of engine combustion particles due to redox-cycling may increase as they age in the atmosphere.
考察了氧化对发动机排气颗粒的氧化还原循环活性的影响。在存在和不存在大量气相排气成分的情况下，使用臭氧在流管中使从二冲程汽油发动机获得的颗粒在一分钟的时间尺度上氧化。尽管臭氧浓度很高，但臭氧暴露量约相当于 60 ppb 臭氧暴露 2-8 小时。使用二硫苏糖醇（DTT）测定法测量，过滤后的颗粒水提取物的氧化还原循环活性显著增加。当整个排气被氧化时，氧化活性的增加主要是由具有氧化还原活性的二次有机气溶胶（SOA）的沉积引起的，导致 DTT 活性的上限为 8.6 ± 2.0 pmol DTT 消耗/ min/μg 颗粒，而新鲜未氧化的排气颗粒为 0.73 ± 0.60 pmol min(-1) μg(-1)。当除去 VOC 的排气被氧化时，氧化还原循环活性达到更高水平，最高 DTT 活性为 16.7 ± 1.6 pmol min(-1) μg(-1)，在所研究的臭氧暴露范围内未达到上限。我们的结果为氧化还原循环可能会随着它们在大气中老化而增加发动机燃烧颗粒毒性的假设提供了实验室支持。
