Shabin Muhammed, Kumar Ashish, Hakkim Haseeb, Rudich Yinon, Sinha Vinayak
Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S.A.S Nagar, Manauli PO, Punjab 140306, India.
Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel.
Sci Total Environ. 2023 Oct 20;896:165281. doi: 10.1016/j.scitotenv.2023.165281. Epub 2023 Jul 4.
Night-time oxidation significantly affects the atmospheric concentration of primary and secondary air pollutants but is poorly constrained over South Asia. Here, using a comprehensively measured and unprecedented set of precursors and sinks of Stabilized Criegee Intermediates (SCI), in the summertime air of the Indo-Gangetic Plain (IGP), we investigate the chemistry, and abundance in detail. This study reports the first summertime levels from the IGP of ethene, propene, 1-butene, cis-2-butene, trans-2-butene, 1-pentene, cis-2-pentene, trans-2-pentene, and 1-hexene and their possible roles in SCI chemistry. Ethene, propene, and 1-butene were the highest ambient alkenes in both the summer and winter seasons. Applying chemical steady-state to the measured precursors, the average calculated SCI concentrations were 4.4 (±3.6) × 10 molecules cm, with Z-CHCHOO (55 %) as the major SCI. Z-RCHOO (35 %) and α-pinene derived PINOO (34 %) were identified as the largest contributors to SCI with a 7.8 × 10 molecules cm s production rate. The peak SCI occurred during the evenings. For all SCI species, the loss was dominated (>50 %) by unimolecular decomposition or reactions with water vapor or water vapor dimer. Pollution events influenced by crop burning resulted in significantly elevated SCI production (2.1 times higher relative to non-polluted periods) reaching as high as (7.4 ± 2.5) × 10 molecules cm s. Among individual SCI species, Z-CHCHOO was highest in all the plume events measured accounting for at least ~41 %. Among alkenes, trans-2-butene was the highest contributor to P(SCI) in plume events ranging from 22 to 32 %. SCIs dominated the night-time oxidation of sulfur dioxide with rates as high as 1.4 (±1.1) × 10 molecules cm s at midnight, suggesting that this oxidation pathway could be a significant source of fine mode sulfate aerosols over the Indo-Gangetic Plain, especially during summertime biomass burning pollution episodes.
夜间氧化显著影响一次和二次空气污染物的大气浓度，但在南亚地区其受约束程度较低。在此，我们利用在印度 - 恒河平原（IGP）夏季空气中对稳定的克里吉中间体（SCI）的前体和汇进行全面测量且前所未有的数据集，详细研究了其化学性质和丰度。本研究报告了IGP地区夏季乙烯、丙烯、1 - 丁烯、顺 - 2 - 丁烯、反 - 2 - 丁烯、1 - 戊烯、顺 - 2 - 戊烯、反 - 2 - 戊烯和1 - 己烯的首个浓度水平及其在SCI化学过程中可能发挥的作用。乙烯、丙烯和1 - 丁烯在夏季和冬季都是环境中含量最高的烯烃。将化学稳态应用于所测量的前体，计算得出的SCI平均浓度为4.4（±3.6）×10分子/立方厘米，其中Z - CHCHOO（55%）为主要的SCI。Z - RCHOO（35%）和α - 蒎烯衍生的PINOO（34%）被确定为SCI的最大贡献者，其生成速率为7.8×10分子/立方厘米·秒。SCI峰值出现在傍晚时分。对于所有SCI物种，损失主要（>50%）由单分子分解或与水蒸气或水蒸气二聚体的反应主导。受作物焚烧影响的污染事件导致SCI生成显著增加（相对于无污染时期高出2.1倍），高达（7.4±2.5）×10分子/立方厘米·秒。在所有测量的羽流事件中，Z - CHCHOO在各个SCI物种中含量最高，至少占~41%。在烯烃中，反 - 2 - 丁烯在羽流事件中对P（SCI）的贡献最高，范围为22%至32%。SCI在夜间二氧化硫氧化过程中占主导地位，午夜时速率高达1.4（±1.1）×10分子/立方厘米·秒，这表明该氧化途径可能是印度 - 恒河平原细模式硫酸盐气溶胶的一个重要来源，特别是在夏季生物质燃烧污染事件期间。
