State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China.
Environ Pollut. 2021 Jan 1;268(Pt B):115952. doi: 10.1016/j.envpol.2020.115952. Epub 2020 Nov 2.
Severe haze episodes in cold season in Beijing have been mitigated greatly during the last decade. However, the changes in aerosol chemistry as responses to the large reductions in gaseous precursors during the two phases of clean air action, i.e., phase Ⅰ (2013-2017) and phase Ⅱ (2018-2020), are less understood. Here we characterized such changes in cold season (January-March) by using five-year real-time aerosol particle composition measurements. Our results showed consistently large reductions for all chemical species from 2013 to 2020 with the largest decreases being chloride (95%) and organics (74%) followed by sulfate (69%), while the decreases in nitrate were comparatively small (44%). However, the contributions of sulfate were fairly stable despite the increased nitrate contributions from 18% in 2013 to 30% in 2020. Organic aerosol (OA) composition also changed significantly since 2018 with large increases in the contributions of secondary OA and corresponding decreases in primary OA from fossil fuel combustion and cooking emissions. The changes in aerosol chemistry were closely related to the different reductions in gaseous precursors, e.g., SO vs. NO, and the enhanced secondary processes, e.g., the increases in O, sulfur and nitrogen oxidation efficiency. Further, we found that the changes in aerosol chemistry in cold season during the phase Ⅱ of clean air action (2018-2020) started to slow down with relatively small changes in PM and secondary inorganic species. Our results point towards a future challenge in mitigating air pollution in cold season, and the need of more stringent and scientific strategies to control secondary aerosol pollution in an environment with enhanced oxidation capacity and high precursors.
过去十年，北京冬季严重雾霾天气已大幅减少。然而，在清洁空气行动计划的两个阶段（第一阶段：2013-2017 年；第二阶段：2018-2020 年），由于气态前体物大幅减少，气溶胶化学性质的变化尚不清楚。本研究通过五年实时气溶胶粒子成分测量，对冬季（1 月至 3 月）的这种变化进行了研究。结果表明，所有化学物质自 2013 年至 2020 年均有大幅减少，其中降幅最大的是氯（95%）和有机物（74%），其次是硫酸盐（69%），而硝酸盐降幅相对较小（44%）。然而，硫酸盐的贡献相对稳定，尽管硝酸盐的贡献从 2013 年的 18%增加到 2020 年的 30%。自 2018 年以来，有机气溶胶（OA）的成分也发生了显著变化，二次有机气溶胶的贡献增加，而化石燃料燃烧和烹饪排放的一次有机气溶胶的贡献相应减少。气溶胶化学的变化与不同的气态前体物（如 SO 与 NO）的减少以及增强的二次过程（如 O、硫和氮氧化效率的提高）密切相关。此外，我们发现，清洁空气行动计划第二阶段（2018-2020 年）冬季气溶胶化学变化开始减缓，PM 和二次无机物种的变化相对较小。研究结果表明，未来在冬季减轻空气污染面临挑战，需要更严格和科学的策略，以控制在氧化能力增强和前体物含量高的环境中二次气溶胶污染。
