Effects of the sample matrix on the photobleaching and photodegradation of toluene-derived secondary organic aerosol compounds
Effects of the sample matrix on the photobleaching and photodegradation of toluene-derived secondary organic aerosol compounds
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DOI：
10.5194/acp-22-10155-2022
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发表时间：
2022-08
影响因子：
6.3
通讯作者：
Alexandra L. Klodt;Marley Adamek;Monica Q. Dibley;S. Nizkorodov;R. O’Brien
中科院分区：
文献类型：
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作者：
Alexandra L. Klodt;Marley Adamek;Monica Q. Dibley;S. Nizkorodov;R. O’Brien
抽象的。二次有机气溶胶（SOA）产生的芳香族化合物在氮氧化物（NOx）的存在下，被称为有效地吸收紫外线和可见光辐射。随着暴露于阳光，SOA中的发色化合物的光降解导致这种类型的SOA缓慢地光漂白。这些光降解反应可能发生在以低浓度溶质为特征的云滴中，或发生在气溶胶颗粒中，气溶胶颗粒可能具有高粘性有机相和具有高浓度无机盐的水相。为了研究周围基质对SOA化合物光降解速率和机制的影响，在烟雾室中通过在NOx存在下甲苯的光氧化制备SOA。收集的SOA在不同条件下使用来自氙弧灯的近紫外辐射（300-400 nm）光解长达24 h：直接在过滤器上、溶解在纯水中以及溶解在1 M硫酸铵中。SOA的质量吸收系数测量作为照射时间的函数，以确定光漂白率。电喷雾电离高分辨质谱耦合液相色谱分离，用于观察SOA组合物的变化所造成的照射。SOA质量吸收系数由于光漂白的下降速率是最快的在水中，与1 M硫酸铵的存在下适度减缓光漂白。相比之下，直接在过滤器上的光漂白较慢。高分辨率质谱分析显示，过滤器上的硝基苯酚化合物的有效的光降解，但不是在水相中，与相对较小的变化观察到的SOA的组合物中照射在水或1 M硫酸铵，尽管更快的光漂白比在过滤器上的样品。这表明硝基酚的光降解在有机相中比在水相中对光漂白的贡献要大得多。我们的结论是SOA的吸收系数寿命相对于光漂白和寿命的各个发色团在SOA的光降解将强烈依赖于样品基质中SOA化合物暴露在阳光下。
Abstract. Secondary organic aerosol (SOA) generated from the photooxidation of aromatic compounds in the presence of oxides of nitrogen (NOx) is known to efficiently absorb ultraviolet and visible radiation. With exposure to sunlight, the photodegradation of chromophoric compounds in the SOA causes this type of SOA to slowly photobleach. These photodegradation reactions may occur in cloud droplets, which are characterized by low concentrations of solutes, or in aerosol particles, which can have highly viscous organic phases and aqueous phases with high concentrations of inorganic salts. To investigate the effects of the surrounding matrix on the rates and mechanisms of photodegradation of SOA compounds, SOA was prepared in a smog chamber by photooxidation of toluene in the presence of NOx. The collected SOA was photolyzed for up to 24 h using near-UV radiation (300–400 nm) from a xenon arc lamp under different conditions: directly on the filter, dissolved in pure water, and dissolved in 1 M ammonium sulfate. The SOA mass absorption coefficient was measured as a function of irradiation time to determine photobleaching rates. Electrospray ionization high-resolution mass spectrometry coupled to liquid chromatography separation was used to observe changes in SOA composition resulting from the irradiation. The rate of decrease in SOA mass absorption coefficient due to photobleaching was the fastest in water, with the presence of 1 M ammonium sulfate modestly slowing down the photobleaching. By contrast, photobleaching directly on the filter was slower. The high-resolution mass spectrometry analysis revealed an efficient photodegradation of nitrophenol compounds on the filter but not in the aqueous phases, with relatively little change observed in the composition of the SOA irradiated in water or 1 M ammonium sulfate despite faster photobleaching than in the on-filter samples. This suggests that photodegradation of nitrophenols contributes much more significantly to photobleaching in the organic phase than in the aqueous phase. We conclude that the SOA absorption coefficient lifetime with respect to photobleaching and lifetimes of individual chromophores in SOA with respect to photodegradation will depend strongly on the sample matrix in which SOA compounds are exposed to sunlight.