Second-Order Kinetic Rate Coefficients for the Aqueous-Phase Hydroxyl Radical (OH) Oxidation of Isoprene-Derived Secondary Organic Aerosol Compounds at 298 K,Environmental Science & Technology

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Second-Order Kinetic Rate Coefficients for the Aqueous-Phase Hydroxyl Radical (OH) Oxidation of Isoprene-Derived Secondary Organic Aerosol Compounds at 298 K
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2021-09-29 , DOI: 10.1021/acs.est.1c04606
Karizza A Abellar ₁ , James D Cope ₂ , Tran B Nguyen ₂

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The hydroxyl radical (OH) oxidation of the most abundant nonmethane volatile organic compound emitted to the atmosphere, isoprene (C₅H₈), produces a number of chemical species that partition to the condensed phase via gas-particle partitioning or form condensed-phase compounds via multiphase/heterogeneous chemistry to generate secondary organic aerosols (SOA). The SOA species in aerosol water or cloud/fog droplets may oxidize further via aqueous reaction with OH radicals, among other fates. Rate coefficients for compounds in isoprene’s photochemical cascade are well constrained in the gas phase; however, a gap of information exists for the aqueous OH rate coefficients of the condensed-phased products, precluding the atmospheric modeling of the oxidative fate of isoprene-derived SOA. This work investigated the OH-initiated oxidation kinetic rate coefficients (k_OH) for six major SOA compounds formed from the high-NO and low-NO channels of isoprene’s atmospheric oxidation and one analog, most of which were synthesized and purified for study: (k₁) 2-methyltetrol [MT: 1.14 (±0.17) × 10⁹ M^–1 s^–1], (k₂) 2-methyl-1,2,3-trihydroxy-4-sulfate [MT-4-S: 1.52 (±0.25) × 10⁹ M^–1 s^–1], (k₃) 2-methyl-1,2-dihydroxy-3-sulfate [MD-3-S: 0.56 (±0.15) × 10⁹ M^–1 s^–1], (k₄) 2-methyl-1,2-dihydroxy-but-3-ene [MDE: 4.35 (±1.16) × 10⁹ M^–1 s^–1], (k₅) 2-methyl-2,3-dihydroxy-1,4-dinitrate [MD-1,4-DN: 0.24 (±0.04) × 10⁹ M^–1 s^–1], (k₆) 2-methyl-1,2,4-trihydroxy-3-nitrate [MT-3-N: 1.12 (±0.15) × 10⁹ M^–1 s^–1], and (k₇) 2-methylglyceric acid [MGA: pH 2:1.41 (±0.49) × 10⁹ M^–1 s^–1; pH 5:0.97 (±0.42) × 10⁹ M^–1 s^–1]. The second-order rate coefficients are determined against the known k_OH of erythritol in pure water. The decays of each reagent were measured with nuclear magnetic resonance (NMR) and high-performance liquid chromatography-high resolution mass spectrometry (HPLC-HRMS). The aqueous photooxidation fates of isoprene-derived SOA compounds are substantial and may impact the SOA budget when implemented into global models.

中文翻译：

异戊二烯衍生的二级有机气溶胶化合物在 298 K 下水相羟基自由基 (OH) 氧化的二阶动力学速率系数

排放到大气中的最丰富的非甲烷挥发性有机化合物的羟基自由基 (OH) 氧化，异戊二烯 (C ₅ H ₈)，产生许多化学物质，它们通过气体-颗粒分配分配到凝聚相或通过多相/多相化学形成凝聚相化合物，以产生二次有机气溶胶 (SOA)。气溶胶水或云/雾滴中的 SOA 物质可能通过与 OH 自由基的水反应进一步氧化，以及其他命运。异戊二烯光化学级联中化合物的速率系数在气相中受到很好的限制；然而，凝聚相产物的含水 OH 速率系数存在信息空白，排除了异戊二烯衍生 SOA 氧化归宿的大气模型。这项工作研究了 OH 引发的氧化动力学速率系数 ( k _OH) 由异戊二烯大气氧化的高 NO 和低 NO 通道形成的六种主要 SOA 化合物和一种类似物，其中大部分合成和纯化用于研究：( k ₁ ) 2-甲基四醇[MT: 1.14 (±0.17) × 10 ⁹ M ^–1 s ^–1 ], ( k ₂ ) 2-methyl-1,2,3-trihydroxy-4-sulfate [MT-4-S: 1.52 (±0.25) × 10 ⁹ M ^–1 s ^{– 1} ], ( k ₃ ) 2-methyl-1,2-dihydroxy-3-sulfate [MD-3-S: 0.56 (±0.15) × 10 ⁹ M ^–1 s ^–1 ], ( k ₄ ) 2-methyl -1,2-二羟基-丁-3-烯 [MDE: 4.35 (±1.16) × 10⁹ M ^–1 s ^–1 ], ( k ₅ ) 2-methyl-2,3-dihydroxy-1,4-dinitrate [MD-1,4-DN: 0.24 (±0.04) × 10 ⁹ M ^–1 s ^{– 1} ], ( k ₆ ) 2-methyl-1,2,4-trihydroxy-3-nitrate [MT-3-N: 1.12 (±0.15) × 10 ⁹ M ^–1 s ^–1 ], 和 ( k ₇ ) 2-甲基甘油酸 [MGA: pH 2:1.41 (±0.49) × 10 ⁹ M ^–1 s ^–1 ; pH 5：0.97 (±0.42) × 10 ⁹ M ^–1 s ^–1 ]。二阶速率系数是根据已知的纯水中赤藓糖醇的k _OH。用核磁共振 (NMR) 和高效液相色谱-高分辨率质谱 (HPLC-HRMS) 测量每种试剂的衰变。异戊二烯衍生的 SOA 化合物的水性光氧化命运是巨大的，并且在实施到全球模型中时可能会影响 SOA 预算。

更新日期：2021-10-19

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