Characterization of Highly Oxidized Molecules in Fresh and Aged Biogenic Secondary Organic Aerosol.
Characterization of Highly Oxidized Molecules in Fresh and Aged Biogenic Secondary Organic Aerosol.
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DOI：
10.1021/acs.analchem.6b00378
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发表时间：
2016-04-19
影响因子：
7.4
通讯作者：
Johnston MV
中科院分区：
文献类型：
--
作者：
Tu P;Hall WA 4th;Johnston MV
在这项工作中，利用高分辨率质谱技术对源自生物前体的新鲜和老化的二次有机气溶胶（SOA）中的高氧化多功能分子（HOMs）进行了表征。在流动管反应器中，将臭氧与生物前体（β-蒎烯、柠檬烯、α-蒎烯）混合生成新鲜SOA。老化是通过将新鲜的SOA通过光化学反应器与羟基自由基反应来完成的。虽然这些气溶胶整体上没有被高度氧化，但分子分析发现其中嵌入了大量的HOMs。新鲜SOA中的HOMs主要由单体和二聚体组成，这与之前的研究中在气相中检测到的极低挥发性有机化合物（ELVOCs）的冷凝一致，并与SOA颗粒的形成有关。老化导致每个HOMs分子的平均碳原子数增加，这与新鲜SOA中已经存在的低聚物（较少氧化）的颗粒相氧化一致。讨论了具有不同氧碳比、氢碳比和平均碳氧化态组合的HOMs，并将其与低挥发性含氧有机气溶胶（lvoa）进行了比较，lvoa是基于平均元素组成在环境气溶胶中确定的，但在分子水平上尚未完全理解。对于所研究的生物源前体和实验条件，新鲜生物源SOA中的HOMs比老化SOA中的HOMs具有更接近于LVOOA的分子式，这表明生物源SOA的老化不能很好地替代环境LVOOA。
In this work, highly oxidized multifunctional molecules (HOMs) in fresh and aged secondary organic aerosol (SOA) derived from biogenic precursors are characterized with high resolution mass spectrometry. Fresh SOA was generated by mixing ozone with a biogenic precursor (β-pinene, limonene, α-pinene) in a flow tube reactor. Aging was performed by passing the fresh SOA through a photochemical reactor where it reacted with hydroxyl radicals. Although these aerosols were as a whole not highly oxidized, molecular analysis identified a significant number of HOMs embedded within it. HOMs in fresh SOA consisted mostly of monomers and dimers, which is consistent with condensation of extremely low-volatility organic compounds (ELVOCs) that have been detected in the gas phase in previous studies and linked to SOA particle formation. Aging caused an increase in the average number of carbon atoms per molecule of the HOMs, which is consistent with particle phase oxidation of (less oxidized) oligomers already existing in fresh SOA. HOMs having different combinations of oxygen-to-carbon ratio, hydrogen-to-carbon ratio and average carbon oxidation state are discussed and compared to low volatility oxygenated organic aerosol (LVOOA), which has been identified in ambient aerosol based on average elemental composition but not fully understood at a molecular level. For the biogenic precursors and experimental conditions studied, HOMs in fresh biogenic SOA have molecular formulas more closely resembling LVOOA than HOMs in aged SOA, suggesting that aging of biogenic SOA is not a good surrogate for ambient LVOOA.