Fine particulate matter (PM_2.5) is a key indicator of urban air quality. Secondary organic aerosol (SOA) contributes substantially to the PM_2.5 concentration. Discrepancies between modeling and field measurements of SOA indicate missing sources and formation mechanisms. Recent studies report elevated concentrations of reactive chlorine species in inland and urban regions, which increase the oxidative capacity of the atmosphere and serve as sources for SOA and particulate chlorides. Chlorine-initiated oxidation of isoprene, the most abundant nonmethane hydrocarbon, is known to produce SOA under pristine conditions, but the effects of anthropogenic influences in the form of nitrogen oxides (NO_x) remain unexplored. Here, we investigate chlorine–isoprene reactions under low- and high-NO_x conditions inside an environmental chamber. Organic chlorides including C₅H₁₁ClO₃, C₅H₉ClO₃, and C₅H₉ClO₄ are observed as major gas- and particle-phase products. Modeling and experimental results show that the secondary OH–isoprene chemistry is significantly enhanced under high-NO_x conditions, accounting for up to 40% of all isoprene oxidized and leading to the suppression of organic chloride formation. Chlorine-initiated oxidation of isoprene could serve as a source for multifunctional (chlorinated) organic oxidation products and SOA in both pristine and anthropogenically influenced environments.

中文翻译：

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NOx 存在下的异戊二烯-氯氧化及其对城市大气化学的影响

细颗粒物 (PM _2.5 ) 是衡量城市空气质量的关键指标。_{二次有机气溶胶 (SOA) 对 PM 2.5}浓度有很大贡献。SOA 的建模和现场测量之间的差异表明缺少来源和形成机制。最近的研究报告称，内陆和城市地区的活性氯物质浓度升高，这增加了大气的氧化能力，并成为 SOA 和颗粒氯化物的来源。众所周知，氯引发的异戊二烯氧化反应是最丰富的非甲烷碳氢化合物，在原始条件下会产生 SOA，但人为影响以氮氧化物（NO _x) 仍未探索。在这里，我们研究了环境室内低和高 NO _{x条件下的氯-异戊二烯反应。}有机氯化物包括 C ₅ H ₁₁ ClO ₃、C ₅ H ₉ ClO ₃和 C ₅ H ₉ ClO ₄被观察为主要的气相和颗粒相产物。建模和实验结果表明，在高 NO _{x条件下，二级 OH-异戊二烯化学显着增强}条件下，占所有异戊二烯的 40% 被氧化并导致抑制有机氯化物的形成。氯引发的异戊二烯氧化可作为原始和人为影响环境中多功能（氯化）有机氧化产物和 SOA 的来源。