Determining the Relative Reactivity of Sulfate, Bisulfate, and Organosulfates with Epoxides on Secondary Organic Aerosol
Determining the Relative Reactivity of Sulfate, Bisulfate, and Organosulfates with Epoxides on Secondary Organic Aerosol
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DOI：
10.1021/acsearthspacechem.0c00178
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发表时间：
2020-10-15
影响因子：
3.4
通讯作者：
Elrod, Matthew J.
中科院分区：
文献类型：
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作者：
Aoki, Erika;Sarrimanolis, Jon N.;Elrod, Matthew J.
广泛的实验室和现场研究已经确定异戊二烯环氧二醇（IEPOX）的亲核加成反应作为异戊二烯衍生的二次有机气溶胶（SOA）形成的关键途径。有机硫酸盐是这些过程的重要反应产物，但目前尚不清楚硫酸盐和/或硫酸氢盐亲核试剂是否是它们形成的原因，以及有机硫酸盐本身是否可以在低聚物形成反应中充当亲核试剂。硫酸根、硫酸氢根和甲基硫酸根阴离子的相对反应性（相对于水的亲核强度）通过使用核磁共振（NMR）光谱的一系列模型环氧化物亲核实验来测量。这些实验也有助于建立一个严格的理解不同的碳取代和功能基团的环氧化物的有效亲核试剂的硫酸根，硫酸氢根和甲基硫酸根阴离子的调制的影响。据确定，硫酸氢根和甲基硫酸根阴离子的亲核试剂分别为约100和50倍，弱于硫酸盐对大多数的环氧化物的研究，这是合理的计算估计其热力学碱度。因此，对于大多数SOA酸度的情况下，硫酸盐-环氧化物反应预计是有机硫酸盐气溶胶成分的主要来源。由于硫酸盐-环氧化物反应化学计量地消耗酸，这些反应也具有提高SOA的pH的能力，从而减缓所有酸催化的化学过程。没有观察到甲基硫酸根阴离子与丰富的大气相关环氧化物反式-β-IEPOX反应的证据，因此表明通过环氧化物-有机硫酸根反应的低聚反应可能无法与实际SOA上更强（如硫酸根）或更丰富（如水）的亲核试剂竞争。
Extensive laboratory and field studies have identified nucleophilic addition reactions of isoprene epoxydiols (IEPOX) as key pathways for the formation of isoprene-derived secondary organic aerosol (SOA). Organosulfates are important reaction products of these processes, but it is unclear whether sulfate and/or bisulfate nucleophiles are responsible for their formation and whether the organosulfates themselves can serve as nucleophiles in oligomer-forming reactions. The relative reactivities (nucleophilic strengths relative to water) of sulfate, bisulfate, and methyl sulfate anion were measured through a series of model epoxide-nucleophile experiments using nuclear magnetic resonance (NMR) spectroscopy. These experiments also helped establish a rigorous understanding of the effects of differing carbon substitution and functional groups of epoxides on the modulation of the effective nucleophilicites of sulfate, bisulfate, and methyl sulfate anions. It was determined that the nucleophilicites of bisulfate and methyl sulfate anions were about 100 and 50 times, respectively, weaker than sulfate toward most of the epoxides studied, which was rationalized by computational estimates of their thermodynamic basicities. Therefore, for most SOA acidity situations, sulfate-epoxide reactions are expected to be the main source of organosulfate aerosol constituents. Because sulfate-epoxide reactions stoichiometrically consume acid, these reactions also have the capability of raising the pH of SOA, thus slowing down all acid-catalyzed chemical processes. No evidence for the reaction of the methyl sulfate anion was observed with the abundant atmospherically relevant epoxide, trans-beta-IEPOX, thus suggesting that oligomerization reactions via epoxide-organosulfate reactions may not be able to compete with stronger (such as sulfate) or more abundant (such as water) nucleophiles on actual SOA.