Reaction of stabilized Criegee intermediates (SCIs) with SO₂ was proposed as an additional pathway of gaseous sulfuric acid (H₂SO₄) formation in the atmosphere, supplementary to the conventional mechanism of H₂SO₄ production by oxidation of SO₂ in reaction with OH radicals. However, because of a large uncertainty in mechanism and rate coefficients for the atmospheric formation and loss reactions of different SCIs, the importance of this additional source is not well established. In this work, we present an estimation of the role of SCIs in H₂SO₄ formation at a western Mediterranean (Cape Corsica) remote site, where comprehensive field observations including gas-phase H₂SO₄, OH radicals, SO₂, volatile organic compounds (VOCs) and aerosol size distribution measurements were performed in July–August 2013 as a part of the project ChArMEx (Chemistry-Aerosols Mediterranean Experiment). The measurement site was under strong influence of local emissions of biogenic volatile organic compounds, including monoterpenes and isoprene generating SCIs in reactions with ozone, and, hence, presenting an additional source of H₂SO₄ via SO₂ oxidation by the SCIs. Assuming the validity of a steady state between H₂SO₄ production and its loss by condensation on existing aerosol particles with a unity accommodation coefficient, about 90 % of the H₂SO₄ formation during the day could be explained by the reaction of SO₂ with OH. During the night the oxidation of SO₂ by OH radicals was found to contribute only about 10 % to the H₂SO₄ formation. The accuracy of the derived values for the contribution of OH + SO₂ reaction to the H₂SO₄ formation is limited mostly by a large, at present factor of 2, uncertainty in the OH + SO₂ reaction rate coefficient. The contribution of the SO₂ oxidation by SCIs to the H₂SO₄ formation was evaluated using available measurements of unsaturated VOCs and steady-state SCI concentrations estimated by adopting rate coefficients for SCI reactions based on structure–activity relationships (SARs). The estimated concentration of the sum of SCIs was in the range of (1–3) × 10³ molec. cm⁻³. During the day the reaction of SCIs with SO₂ was found to account for about 10 % and during the night for about 40 % of the H₂SO₄ production, closing the H₂SO₄ budget during the day but leaving unexplained about 50 % of the H₂SO₄ formation during the night. Despite large uncertainties in used kinetic parameters, these results indicate that the SO₂ oxidation by SCIs may represent an important H₂SO₄ source in VOC-rich environments, especially during nighttime.

中文翻译：

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Criegee 中间体在地中海（科西嘉角）受生物排放影响的硫酸形成过程中的作用

稳定克里奇中间体（的SCI）与SO的反应₂，提出了作为气态硫酸（H的附加通路₂ SO ₄）在大气中形成，补充到H的常规机构₂ SO ₄通过的SO氧化生产₂在反应与 OH 自由基。然而，由于不同 SCI 的大气形成和损失反应的机制和速率系数存在很大的不确定性，因此这种额外来源的重要性尚未得到很好的证实。在这项工作中，我们估计了 SCI 在 H ₂ SO _{4 中的作用}地中海西部（科西嘉角）偏远地点的地层，在2013 年 7 月至 8 月期间进行了包括气相 H ₂ SO ₄、OH 自由基、SO ₂、挥发性有机化合物 (VOC) 和气溶胶粒径分布测量在内的综合现场观测，如ChArMEx（化学气溶胶地中海实验）项目的一部分。测量地点受到生物挥发性有机化合物（包括单萜和异戊二烯）与臭氧反应产生 SCI 的局部排放的强烈影响，因此，通过SCI 的SO ₂氧化提供了额外的 H ₂ SO ₄来源。假设 H ₂ SO之间的稳态有效性_{4 的}产生及其在具有统一调节系数的现有气溶胶颗粒上冷凝造成的损失，在白天形成的 H ₂ SO _{4 的}大约 90%可以通过 SO ₂与 OH的反应来解释。发现在夜间，OH 自由基对 SO ₂的氧化对H ₂ SO _{4 的}形成仅贡献约 10%。OH +  SO ₂反应对 H ₂ SO ₄ 形成的贡献的导出值的准确性 主要受到 OH +  SO _{2 中}很大的、目前为 2 的不确定性的限制 反应速率系数。SCIs 氧化SO ₂对 H ₂ SO ₄形成的贡献是通过使用基于结构-活性关系 (SARs) 的 SCI 反应的速率系数估计的不饱和 VOC 和稳态 SCI 浓度的可用测量来评估的。这 SCIs总和的估计浓度在 (1-3) ×  10 ³ molec的范围内 。厘米^-3。发现SCI 与 SO ₂的反应在白天约占 H ₂ SO ₄产量的10 %，而在夜间约占 H ₂ SO ₄产量的40 %， 在白天关闭了 H ₂ SO ₄预算，但仍有约 50 % 无法解释在夜间形成H ₂ SO ₄。尽管使用的动力学参数存在很大的不确定性，但这些结果表明SCI对 SO _{2 的}氧化可能代表重要的 H ₂ SO ₄ 源在富含 VOC 的环境中，尤其是在夜间。