A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol
A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol
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4-乙基苯酚水相光化学氧化的综合研究
DOI：
10.1016/j.scitotenv.2019.06.276
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发表时间：
2019
影响因子：
9.8
通讯作者：
Ge Xinlei
中科院分区：
文献类型：
--
作者：
Ye Zhaolian;Qu Zhenxiu;Ma Shuaishuai;Luo Shipeng;Chen Yantong;Chen Hui;Chen Yanfang;Zhao Zhuzi;Chen Mindong;Ge Xinlei
大气水相中的二次有机气溶胶（secondary organic aerosol，SOA）是细颗粒气溶胶的重要组成部分，也是国际上公认的人类健康风险因子。本文首次系统研究了生物质燃烧模型化合物4-乙基苯酚（4-EP）在紫外（UV）（汞灯）和模拟日光（氙灯）下的水相光化学氧化反应。结果表明，在紫外光下，4-EP被羟基自由基（radical dotOH）氧化降解的速度比在模拟太阳光下快近15倍，但在两种条件下均能得到较高的SOA水溶液（aqSOA）产率（108%~ 122%）。AqSOA的质量和氧化态在模拟太阳光下不断增加，但在紫外光下，它们先增加后迅速下降。我们提出了一个反应方案的基础上确定的产品，显示低聚，功能化和断裂都可以发生在4-EP氧化。我们的研究结果表明，自由基dotOH自由基可能会抑制齐聚和功能化，但有利于断裂。在H2 O2（高自由基dotOH）的紫外光照射下，裂解作用占主导地位，生成更多挥发性小分子，后期氧化生成的aqSOA较少;在H2 O2（中自由基dotOH）的模拟日光照射下，形成羟基化单体的功能化作用更为重要。有机三重激发态（3C*）氧化4-EP形成的物种比OH氧化的物种具有更强的可见光吸收，且吸收率与类腐殖酸含量呈正相关。
Secondary organic aerosol (SOA) species formed in atmospheric aqueous phases is recently recognized as an important contributor to fine aerosols, which is known to be a prominent human health risk factor internationally. This work, for the first time, systematically investigated aqueous-phase photochemical oxidation of 4-ethylphenol (4-EP) - a model compound from biomass burning and a surrogate of intermediate volatility organic compounds, under both ultraviolet (UV) (Hg lamp) and simulated sunlight (Xe lamp). We found that 4-EP could degrade upon hydroxal radical (radical dotOH) oxidation under UV light nearly 15 times faster than that under simulated sunlight, but large aqueous SOA (aqSOA) yields (108%–122%) were observed under both situations. AqSOA masses and oxidation states continuously increased under simulated sunlight, yet they increased first then decreased quickly under UV light. We proposed a reaction scheme based on identified products, showing that oligomerization, functionalization and fragmentation all can occur during 4-EP oxidation. Our results demonstrate that radical dotOH radical may suppress oligomerization and functionalization, but is favorable for fragmentation. Under UV light with H2O2(high radical dotOH), fragmentation was dominant, producing more volatile and smaller molecules, and less aqSOA in later oxidation; Under simulated sunlight with H2O2(moderate radical dotOH), functionalization that can form hydroxylated monomer was more important. Moreover, 4-EP oxidation by the organic triplet excited state (3C*) could form species with stronger visible light absorptivity than those from OH-mediated oxidation, and the absorptivity showed positive link with contents of humic-like substances.