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Formation of aqueous-phase secondary organic aerosols from glycolaldehyde and ammonium sulfate/amines: A kinetic and mechanistic study
Atmospheric Environment ( IF 5 ) Pub Date : 2018-05-01 , DOI: 10.1016/j.atmosenv.2018.03.021
Yayi Yi , Zhaoyu Cao , Xuehua Zhou , Likun Xue , Wenxing Wang

Abstract Atmospheric particles are largely represented by secondary organic aerosols (SOAs) produced by either aqueous- or gas-phase reactions. Recently, the contribution of the former to SOA formation has been shown to substantially increase and even reach that of the latter, which necessitates in-depth mechanistic investigations. For a deeper understanding of aqueous-phase SOA generation, we herein studied the production of these aerosols in the dark from glycolaldehyde (GAld) and ammonium sulfate (AS)/amines (methylamine (MAm) and glycine (Gly)). UV–vis spectroscopy showed that reaction mixtures featured two main absorption bands (at 209–230 and 280–330 nm) that were attributed to the π–π* transitions of Schiff bases and the n–π* transitions of oligomers produced in the above reactions, respectively. Further studies revealed that irrespective of reactant concentration and pH, all the investigated reactions were well fitted by first-order kinetics and were accelerated by increasing AS/MAm concentrations and solution pH under acidic conditions. The reaction rate constants (determined from changes of absorption at 300 nm) followed the order of Gly (kI = 2.39 × 10−6 s−1) > MAm (kI = 1.19 × 10−6 s−1) > AS (kI = 8.33 × 10−7 s−1) at identical low AS/amine concentrations and were in the order of MAm (kI = 2.5 × 10−6 s−1) > AS (kI = 1.39 × 10−6 s−1) at high AS/MAm concentrations. The main reaction pathways corresponded to the aldol self-condensation of GAld and the nucleophilic attack of AS/amines on GAld followed by dehydration, which afforded imines as the major products. The stronger light absorption of (GAld + Gly) mixtures than that of (glyoxal/methylglyoxal + Gly) mixtures was ascribed to the increased amount of imine- and carbonyl group-containing products produced in the former case.

中文翻译:

由乙醇醛和硫酸铵/胺形成水相二次有机气溶胶:动力学和机理研究

摘要 大气颗粒主要由水相或气相反应产生的二次有机气溶胶 (SOA) 表示。最近,前者对 SOA 形成的贡献已被证明显着增加甚至达到后者,这需要深入的机理研究。为了更深入地了解水相 SOA 的生成,我们在此研究了在黑暗中由乙醇醛 (GAld) 和硫酸铵 (AS)/胺(甲胺 (MAm) 和甘氨酸 (Gly))产生的这些气溶胶。UV-vis 光谱显示反应混合物具有两个主要吸收带(在 209-230 和 280-330 nm),这归因于席夫碱的 π-π* 跃迁和上述制备的低聚物的 n-π* 跃迁反应,分别。进一步的研究表明,无论反应物浓度和 pH 值如何,所有研究的反应都符合一级动力学,并且在酸性条件下通过增加 AS/MAm 浓度和溶液 pH 值来加速。反应速率常数(由 300 nm 处的吸收变化确定)遵循 Gly (kI = 2.39 × 10−6 s−1) > MAm (kI = 1.19 × 10−6 s−1) > AS (kI = 8.33 × 10−7 s−1) 在相同的低 AS/胺浓度下,顺序为 MAm (kI = 2.5 × 10−6 s−1) > AS (kI = 1.39 × 10−6 s−1) 在高 AS/MAm 浓度。主要反应途径对应于 GAld 的羟醛自缩合和 AS/胺对 GAld 的亲核攻击,然后脱水,得到亚胺作为主要产物。
更新日期:2018-05-01
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