Both NOx and SO are important anthropogenic air pollutants that significantly affect secondary organic aerosols (SOA) formation. However, our understanding of the combined effects of NOx and SO on SOA formation is still insufficient. The concentrations, optical properties, and chemical compositions of SOA formed through -xylene photooxidation under various NOx concentrations were investigated with or without SO in the chamber. It was found that SOA mass concentration increased from 60 to 129 μg m when the initial NOx concentration was increased from 0 to 900 ppb. The presence of 50 ppb SO not only enhanced -xylene SOA formation by 1.6–2.9 times, but also changed the evolution of SOA with NOx. The enhancement of -xylene SOA formation was primarily attributed to acid-catalyzed heterogeneous reactions initiated by nitric acid and sulfuric acid. However, SOA concentration decreased under 900 ppb NOx when SO was present, likely due to the decrease in sulfate production because of the competition between NOx and SO for ·OH. In addition, nitrogen-containing organic compounds (NOCs) concentrations and mass absorption coefficients (MAC) were promoted by both NOx and SO. Our research indicates that the promotion of both NOCs formation by NOx, and oligomer formation by SO were the main reasons for the enhanced SOA light absorption. The present research provides a scientific basis for understanding the combined effects of both NOx and SO on -xylene SOA formation, and illustrates that the imbalanced reduction of anthropogenic air pollutants would lead to new characteristics in SOA pollution.

中文翻译：

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NOx和SO2对邻二甲苯光氧化二次有机气溶胶形成和光吸收的协同作用

NOx 和 SO 都是重要的人为空气污染物，会显着影响二次有机气溶胶 (SOA) 的形成。然而，我们对 NOx 和 SO 对 SOA 形成的综合影响的理解仍然不足。研究了在室内有或没有 SO 的情况下，在不同 NOx 浓度下通过对二甲苯光氧化形成的 SOA 的浓度、光学性质和化学成分。结果发现，当初始NOx浓度从0增加到900 ppb时，SOA质量浓度从60增加到129 μg m。 50 ppb SO 的存在不仅使二甲苯 SOA 的形成增强了 1.6-2.9 倍，而且还改变了 SOA 与 NOx 的演变。对二甲苯SOA 形成的增强主要归因于由硝酸和硫酸引发的酸催化非均相反应。然而，当 SO 存在时，SOA 浓度降至 900 ppb NOx 以下，这可能是由于 NOx 和 SO 之间对·OH 的竞争导致硫酸盐产量减少。此外，NOx 和 SO 都会提高含氮有机化合物 (NOC) 浓度和质量吸收系数 (MAC)。我们的研究表明，NOx 促进 NOC 形成和 SO 促进低聚物形成是 SOA 光吸收增强的主要原因。本研究为理解NOx和SO对二甲苯SOA形成的综合影响提供了科学依据，并说明人为空气污染物的不平衡减少将导致SOA污染的新特征。