Acylperoxy Radicals as Key Intermediates in the Formation of Dimeric Compounds in α-Pinene Secondary Organic Aerosol,Environmental Science & Technology

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Acylperoxy Radicals as Key Intermediates in the Formation of Dimeric Compounds in α-Pinene Secondary Organic Aerosol
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2022-09-30 , DOI: 10.1021/acs.est.2c02090
Yue Zhao ₁ , Min Yao ₁ , Yingqi Wang ₁ , Ziyue Li ₁ , Shunyao Wang ₁ , Chenxi Li ₁ , Huayun Xiao ₁

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High molecular weight dimeric compounds constitute a significant fraction of secondary organic aerosol (SOA) and have profound impacts on the properties and lifecycle of particles in the atmosphere. Although different formation mechanisms involving reactive intermediates and/or closed-shell monomeric species have been proposed for the particle-phase dimers, their relative importance remains in debate. Here, we report unambiguous experimental evidence of the important role of acyl organic peroxy radicals (RO₂) and a small but non-negligible contribution from stabilized Criegee intermediates (SCIs) in the formation of particle-phase dimers during ozonolysis of α-pinene, one of the most important precursors for biogenic SOA. Specifically, we find that acyl RO₂-involved reactions explain 50–80% of total oxygenated dimer signals (C₁₅–C₂₀, O/C ≥ 0.4) and 20–30% of the total less oxygenated (O/C < 0.4) dimer signals. In particular, they contribute to 70% of C₁₅–C₁₉ dimer ester formation, likely mainly via the decarboxylation of diacyl peroxides arising from acyl RO₂ cross-reactions. In comparison, SCIs play a minor role in the formation of C₁₅–C₁₉ dimer esters but react noticeably with the most abundant C₉ and C₁₀ carboxylic acids and/or carbonyl products to form C₁₉ and C₂₀ dimeric peroxides, which are prone to particle-phase transformation to form more stable dimers without the peroxide functionality. This work provides a clearer view of the formation pathways of particle-phase dimers from α-pinene oxidation and would help reduce the uncertainties in future atmospheric modeling of the budget, properties, and health and climate impacts of SOA.

中文翻译：

酰基过氧自由基作为 α-蒎烯二级有机气溶胶中二聚化合物形成的关键中间体

高分子量二聚化合物构成二次有机气溶胶 (SOA) 的重要组成部分，并对大气中颗粒的性质和生命周期产生深远影响。尽管已经为颗粒相二聚体提出了涉及反应性中间体和/或闭壳单体种类的不同形成机制，但它们的相对重要性仍然存在争议。_{在这里，我们报告了酰基有机过氧自由基 (RO 2} )的重要作用的明确实验证据，以及稳定的 Criegee 中间体 (SCI) 在 α-蒎烯臭氧分解过程中颗粒相二聚体形成中的小但不可忽略的贡献，生物源 SOA 最重要的先驱之一。具体来说，我们发现酰基 RO ₂- 涉及的反应解释了总氧化二聚体信号的 50-80%（C ₁₅ –C ₂₀，O/C ≥ 0.4）和总氧化较少（O/C < 0.4）二聚体信号的 20-30%。特别是，它们有助于 70% 的 C ₁₅ -C _{19二聚酯形成，可能主要是通过由酰基 RO}₂交叉反应产生的二酰基过氧化物的脱羧。相比之下，SCI 在 C ₁₅ -C _{19 二}聚酯的形成中起次要作用，但与最丰富的 C ₉和 C ₁₀羧酸和/或羰基产物反应形成 C ₁₉和 C ₂₀二聚过氧化物，易于发生颗粒相变以形成更稳定的二聚体，而没有过氧化物官能团。这项工作为 α-蒎烯氧化形成颗粒相二聚体的途径提供了一个更清晰的视角，并将有助于减少未来大气建模中 SOA 的预算、性质、健康和气候影响的不确定性。

更新日期：2022-09-30

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