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DOI	10.5194/acp-19-139-2019
	Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging
	Li C.; He Q.; Schade J.; Passig J.; Zimmermann R.; Meidan D.; Laskin A.; Rudich Y.
发表日期	2019
ISSN	16807316
起始页码	139
结束页码	163
卷号	19 期号:1
英文摘要	Following wood pyrolysis, tar ball aerosols were laboratory generated from wood tar separated into polar and nonpolar phases. Chemical information of fresh tar balls was obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and single-particle laser desorption/resonance enhanced multiphoton ionization mass spectrometry (SP-LD-REMPI-MS). Their continuous refractive index (RI) between 365 and 425 nm was retrieved using a broadband cavity enhanced spectroscopy (BBCES). Dynamic changes in the optical and chemical properties for the nonpolar tar ball aerosols in NOx-dependent photochemical process were investigated in an oxidation flow reactor (OFR). Distinct differences in the chemical composition of the fresh polar and nonpolar tar aerosols were identified. Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (e.g., methoxy-phenols, benzenediol) with higher O : C ratios and carbon oxidation states. Fresh tar balls have light absorption characteristics similar to atmospheric brown carbon (BrC) aerosol with higher absorption efficiency towards the UV wavelengths. The average retrieved RI is 1.661+0.020i and 1.635+0.003i for the nonpolar and polar tar aerosols, respectively, with an absorption Ångström exponent (AAE) between 5.7 and 7.8 in the detected wavelength range. The RI fits a volume mixing rule for internally mixed nonpolar/polar tar balls. The RI of the tar ball aerosols decreased with increasing wavelength under photochemical oxidation. Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls. Oxidation under varying OH exposure levels and in the absence of NOx diminished the absorption (bleaching) and increased the O : C ratio of the tar balls. The photobleaching via OH radical initiated oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components in the aged particles. Photolysis of nitrous oxide (N2O) was used to simulate NOx-dependent photochemical aging of tar balls in the OFR. Under high-NOx conditions with similar OH exposure, photochemical aging led to the formation of organic nitrates, and increased both oxidation degree and light absorption for the aged tar ball aerosols. These observations suggest that secondary organic nitrate formation counteracts the bleaching by OH radical photooxidation to eventually regain some absorption of the aged tar ball aerosols. The atmospheric implication and climate effects from tar balls upon various oxidation processes are briefly discussed. © 2019 Copernicus. All rights reserved.
语种	英语
scopus关键词	aerosol composition; aging; chemical composition; mass spectrometry; nitrous oxide; optical property; PAH; photochemistry; photolysis; pyrolysis
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/144743
作者单位	Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, 76100, Israel; Joint Mass Spectrometry Centre, University of Rostock, Dr.-Lorenz-Weg 2, Rostock, 18059, Germany; Joint Mass Spectrometry Centre, Cooperation Group Comprehensive Molecular Analytics (CMA), Helmholtz Zentrum München, Ingolstädter Landstrasse 1, Neuherberg, 85764, Germany; Department of Chemistry, Purdue University, West Lafayette, IN 47907, United States
推荐引用方式 GB/T 7714	Li C.,He Q.,Schade J.,et al. Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging[J],2019,19(1).
APA	Li C..,He Q..,Schade J..,Passig J..,Zimmermann R..,...&Rudich Y..(2019).Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging.Atmospheric Chemistry and Physics,19(1).
MLA	Li C.,et al."Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging".Atmospheric Chemistry and Physics 19.1(2019).