State Key Joint Laboratory of Environmental Simulation and Pollution Control, BIC-ESAT and IJRC, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm 11418, Sweden.
Environ Sci Technol. 2021 Dec 7;55(23):15680-15693. doi: 10.1021/acs.est.1c04255. Epub 2021 Nov 13.
Molecular analyses help to investigate the key precursors and chemical processes of secondary organic aerosol (SOA) formation. We obtained the sources and molecular compositions of organic aerosol in PM in winter in Beijing by online and offline mass spectrometer measurements. Photochemical and aqueous processing were both involved in producing SOA during the haze events. Aromatics, isoprene, long-chain alkanes or alkenes, and carbonyls such as glyoxal and methylglyoxal were all important precursors. The enhanced SOA formation during the severe haze event was predominantly contributed by aqueous processing that was promoted by elevated amounts of aerosol water for which multifunctional organic nitrates contributed the most followed by organic compounds having four oxygen atoms in their formulae. The latter included dicarboxylic acids and various oxidation products from isoprene and aromatics as well as products or oligomers from methylglyoxal aqueous uptake. Nitrated phenols, organosulfates, and methanesulfonic acid were also important SOA products but their contributions to the elevated SOA mass during the severe haze event were minor. Our results highlight the importance of reducing nitrogen oxides and nitrate for future SOA control. Additionally, the formation of highly oxygenated long-chain molecules with a low degree of unsaturation in polluted urban environments requires further research.
分子分析有助于研究二次有机气溶胶（SOA）形成的关键前体和化学过程。我们通过在线和离线质谱仪测量，获得了北京冬季 PM 中有机气溶胶的来源和分子组成。在雾霾事件中，光化学和水相过程都参与了 SOA 的生成。芳烃、异戊二烯、长链烷烃或烯烃以及如乙二醛和甲基乙二醛的羰基化合物都是重要的前体。在严重雾霾事件中，SOA 形成的增强主要归因于水相过程，这是由气溶胶水含量的增加所促进的，其中多功能有机硝酸盐的贡献最大，其次是分子式中含有四个氧原子的有机化合物。后者包括来自异戊二烯和芳烃的二羧酸和各种氧化产物以及甲基乙二醛水吸收的产物或低聚物。硝化酚、有机硫酸盐和甲磺酸也是重要的 SOA 产物，但它们对严重雾霾事件中 SOA 质量升高的贡献较小。我们的结果强调了减少氮氧化物和硝酸盐对未来 SOA 控制的重要性。此外，在污染的城市环境中形成具有低不饱和度的高度含氧长链分子需要进一步研究。
