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DOI	10.5194/acp-19-6579-2019
	Photooxidants from brown carbon and other chromophores in illuminated particle extracts
	Kaur R.; Labins J.R.; Helbock S.S.; Jiang W.; Bein K.J.; Zhang Q.; Anastasio C.
发表日期	2019
ISSN	16807316
起始页码	6579
结束页码	6594
卷号	19 期号:9
英文摘要	While photooxidants are important in atmospheric condensed phases, there are very few measurements in particulate matter (PM). Here we measure light absorption and the concentrations of three photooxidants-hydroxyl radical ( •OH), singlet molecular oxygen (1O2∗), and oxidizing triplet excited states of organic matter (3O∗)-in illuminated aqueous extracts of wintertime particles from Davis, California. 1O2∗ and 3O∗, which are formed from photoexcitation of brown carbon (BrC), have not been previously measured in PM. In the extracts, mass absorption coefficients for dissolved organic compounds (MACDOC) at 300 nm range between 13 000 and 30 000 cm2 (g C)-1 are approximately twice as high as previous values in Davis fogs. The average .(±1σ)•OH steady-state concentration in particle extracts is 4:4.(±2.3)×10-16 M, which is very similar to previous values in fog, cloud, and rain: although our particle extracts are more concentrated, the resulting enhancement in the rate of •OH photoproduction is essentially canceled out by a corresponding enhancement in concentrations of natural sinks for •OH. In contrast, concentrations of the two oxidants formed primarily from brown carbon (i.e., 1O2∗ and 3O∗) are both enhanced in the particle extracts compared to Davis fogs, a result of higher concentrations of dissolved organic carbon and faster rates of light absorption in the extracts. The average 1O2∗ concentration in the PM extracts is 1.6(±0.5)×10-12 M, 7 times higher than past fog measurements, while the average concentration of oxidizing triplets is 1.0(±0:4)×10-13 M, nearly double the average Davis fog value. Additionally, the rates of 1O2∗ and 3O∗ photoproduction are both well correlated with the rate of sunlight absorption. Since we cannot experimentally measure photooxidants under ambient particle water conditions, we measured the effect of PM dilution on oxidant concentrations and then extrapolated to ambient particle conditions. As the particle mass concentration in the extracts increases, measured concentrations of •OH remain relatively unchanged, 1O2∗ increases linearly, and 3O∗ concentrations increase less than linearly, likely due to quenching by dissolved organics. Based on our measurements, and accounting for additional sources and sinks that should be important under PM conditions, we estimate that [ •OH] in particles is somewhat lower than in dilute cloud/fog drops, while [3O∗] is 30 to 2000 times higher in PM than in drops, and [1O2∗] is enhanced by a factor of roughly 2400 in PM compared to drops. Because of these enhancements in 1O2∗ and 3O∗ concentrations, the lifetimes of some highly soluble organics appear to be much shorter in particle liquid water than under foggy/cloudy conditions. Based on extrapolating our measured rates of formation in PM extracts, BrC-derived singlet molecular oxygen and triplet excited states are overall the dominant sinks for organic compounds in particle liquid water, with an aggregate rate of reaction for each oxidant that is approximately 200-300 times higher than the aggregate rate of reactions for organics with •OH. For individual, highly soluble reactive organic compounds it appears that 1O2∗ is often the major sink in particle water, which is a new finding. Triplet excited states are likely also important in the fate of individual particulate organics, but assessing this requires additional measurements of triplet interactions with dissolved organic carbon in natural samples. © Author(s) 2019.
语种	英语
scopus关键词	aerosol composition; brown carbon; concentration (composition); condensation; dissolved organic carbon; particulate matter; photooxidation; radical; California; Davis; United States
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144401
作者单位	Department of Land, Air and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616-8627, United States; Department of Environmental Toxicology, University of California, Davis, One Shields Avenue, Davis, CA 95616-8627, United States; Center for Health and the Environment, University of California, Davis, One Shields Avenue, Davis, CA 95616-8627, United States
推荐引用方式 GB/T 7714	Kaur R.,Labins J.R.,Helbock S.S.,et al. Photooxidants from brown carbon and other chromophores in illuminated particle extracts[J],2019,19(9).
APA	Kaur R..,Labins J.R..,Helbock S.S..,Jiang W..,Bein K.J..,...&Anastasio C..(2019).Photooxidants from brown carbon and other chromophores in illuminated particle extracts.Atmospheric Chemistry and Physics,19(9).
MLA	Kaur R.,et al."Photooxidants from brown carbon and other chromophores in illuminated particle extracts".Atmospheric Chemistry and Physics 19.9(2019).