Fresh versus Photo-recalcitrant Secondary Organic Aerosol: Effects of Organic Mixtures on Aqueous Photodegradation of 4-Nitrophenol,Environmental Science & Technology Letters

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Fresh versus Photo-recalcitrant Secondary Organic Aerosol: Effects of Organic Mixtures on Aqueous Photodegradation of 4-Nitrophenol
Environmental Science & Technology Letters ( IF 8.9 ) Pub Date : 2020-03-06 , DOI: 10.1021/acs.estlett.0c00177
Tanner Braman ₁ , Lydia Dolvin ₁ , Corey Thrasher ₁ , Hongmin Yu ₁ , Emma Q. Walhout ₁ , Rachel E. O’Brien ₁

Affiliation

In the atmosphere, brown carbon (BrC) molecules can contribute to photochemistry and to the warming and evaporation of cloud droplets. The lifetimes of BrC molecules in these cloud droplets are not well constrained, especially considering the droplets can contain mixtures of organic and inorganic molecules. Here we investigated the kinetics of photodegradation for a representative brown carbon molecule, 4-nitrophenol (4NP), in aqueous solutions at low pH. Three different solutions were compared: one containing 4NP alone and the other two additionally containing either fresh or photo-recalcitrant (pre-photobleached) α-pinene secondary organic aerosol (SOA). Fresh SOA slightly accelerates the photodegradation compared to that with 4NP alone. In contrast, photo-recalcitrant SOA decelerates photodegradation, increasing the estimated atmospheric lifetime of 4NP by 4 h (from ∼11 h for BrC alone to ∼14 h when it is mixed with photo-recalcitrant SOA). Photo-recalcitrant SOA also shows minimal chemical changes after irradiation for 20 h in aqueous solution. These results suggest that, in contrast to fresh SOA, aqueous photo-recalcitrant SOA does not serve as a source of OH radicals when irradiated but may instead act as an OH radical scavenger. The presence of photo-recalcitrant SOA could have important effects on atmospheric lifetimes of organics in mixed aqueous systems.

中文翻译：

新鲜与光顽固的次要有机气溶胶：有机混合物对4-硝基苯酚水溶液光降解的影响

在大气中，棕碳（BrC）分子可促进光化学作用以及云滴的加热和蒸发。这些云滴中的BrC分子的寿命并没有受到很好的限制，特别是考虑到这些滴可以包含有机和无机分子的混合物时。在这里，我们研究了在低pH水溶液中代表性的棕色碳分子4-硝基苯酚（4NP）的光降解动力学。比较了三种不同的溶液：一种溶液仅包含4NP，另一种溶液另外包含新鲜的或光难分解的（预光漂白的）α-pine烯二次有机气溶胶（SOA）。与单独使用4NP相比，新鲜的SOA略微加速了光降解。相比之下，抗拒光的SOA会降低光降解能力，将4NP的估计大气寿命增加了4小时（从单独的BrC的约11 h到与光阻挠性SOA混合的约14 h）。光顽固型SOA在水溶液中照射20小时后，化学变化也很小。这些结果表明，与新鲜的SOA相比，水性光顽固性SOA在被辐照时不会充当OH自由基的来源，而可能会充当OH自由基清除剂。光阻挠性SOA的存在可能会对混合水体系中有机物的大气寿命产生重要影响。水性光顽固性SOA在被辐照时不能用作OH自由基的来源，而可以用作OH自由基清除剂。光阻挠性SOA的存在可能会对混合水体系中有机物的大气寿命产生重要影响。水性光顽固性SOA在被辐照时不能用作OH自由基的来源，而可以用作OH自由基清除剂。光阻挠性SOA的存在可能会对混合水体系中有机物的大气寿命产生重要影响。

更新日期：2020-04-23

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