State Key Laboratory of Loess and Quaternary Geology, Center for Excellence in Quaternary Science and Global Change, and Key Laboratory of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Loess and Quaternary Geology, Center for Excellence in Quaternary Science and Global Change, and Key Laboratory of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China.
Environ Int. 2020 Jul;140:105732. doi: 10.1016/j.envint.2020.105732. Epub 2020 Apr 28.
To mitigate air pollution in China, a legislative 'Air Pollution Prevention and Control Action Plan' has been implemented by the Chinese government since 2013. There is, however, a lack of investigations for long-term trends in the composition, sources and evolution processes of PM (particulate matter with diameter less than 1 μm) after the implementation. To evaluate the effectiveness of these control measures, we present a year-long real-time measurement of the chemical composition of PM at an urban site in Beijing from November 2014 to November 2015, and the results are compared with previous studies from 2008 to 2013 to gain insights into the variations of the chemical composition and sources of PM in Beijing. Large seasonal differences were observed in the mass concentrations of PM species and general declining trend was observed in the last seven years. Specifically, the annual averages of mass concentrations in 2014-2015 decrease by 16-43% (PM), 23-43% (organic aerosol, OA), 38-68% (sulfate), 26-51% (nitrate), 18-33% (ammonium) and 27-38% (chloride) compared to those from 2008 to 2013. During winter and summer, the seasonal mass concentrations of sulfate and nitrate show more significant declines especially in summer 2008 (79% and 81%) and summer 2011 (76% and 77%). The nitrate-to-sulfate ratio is higher in 2014-2015 (1.5 ± 0.6) than that in 2013 (1.0 ± 0.3), largely due to significant reduction in SO emissions, suggesting that nitrate is becoming more important than sulfate in particulate pollution in Beijing. OA is the dominant PM fraction (>45%) in all seasons and the mass concentrations/contributions of both primary and secondary OA show different seasonality. As for the more oxidized oxygenated OA (MO-OOA) and less oxidized oxygenated OA (LO-OOA), the contributions of MO-OOA are much higher than those of LO-OOA (27-62% vs. 6-26%) in both high-pollution and low-pollution days. Aqueous-phase processes are found to facilitate the formation of MO-OOA while photochemical oxidation formation is a major contributor of LO-OOA in winter, and photochemical oxidation plays a major role in the formation of MO-OOA in summer and fall. The current study provides a comprehensive seasonal comparison of chemical composition and formation of PM in Beijing and a pacesetter in tackling PM pollution for other equally polluted megacities, after implementation of more stringent control measures after 2013.
为了减轻中国的空气污染，中国政府自 2013 年以来实施了一项立法的“空气污染防治行动计划”。然而，在实施之后，对于 PM（直径小于 1μm 的颗粒物）组成、来源和演化过程的长期趋势缺乏调查。为了评估这些控制措施的有效性，我们在 2014 年 11 月至 2015 年 11 月期间在北京的一个城市地点进行了为期一年的 PM 化学成分实时测量，并将结果与 2008 年至 2013 年的先前研究进行了比较，以深入了解北京 PM 化学成分和来源的变化。PM 物种的质量浓度存在明显的季节性差异，过去七年呈总体下降趋势。具体来说，2014-2015 年的年均质量浓度比 2008-2013 年下降了 16-43%（PM）、23-43%（有机气溶胶，OA）、38-68%（硫酸盐）、26-51%（硝酸盐）、18-33%（铵）和 27-38%（氯化物）。在冬季和夏季，硫酸盐和硝酸盐的季节性质量浓度下降更为显著，尤其是在 2008 年冬季（79%和 81%）和 2011 年夏季（76%和 77%）。硝酸盐与硫酸盐的比值在 2014-2015 年（1.5±0.6）高于 2013 年（1.0±0.3），这主要是由于 SO 排放的显著减少，表明硝酸盐在北京市颗粒物污染中比硫酸盐更为重要。OA 是所有季节中 PM 的主要部分（>45%），并且一次和二次 OA 的质量浓度/贡献显示出不同的季节性。对于更氧化的含氧 OA（MO-OOA）和较少氧化的含氧 OA（LO-OOA），在高污染和低污染日，MO-OOA 的贡献远高于 LO-OOA（27-62%比 6-26%）。水相过程有利于 MO-OOA 的形成，而光化学氧化形成是冬季 LO-OOA 的主要贡献者，光化学氧化在夏季和秋季 MO-OOA 的形成中起着主要作用。本研究提供了北京 PM 化学组成和形成的全面季节性比较，并且是在 2013 年之后实施更严格的控制措施后，其他同等污染的特大城市应对 PM 污染的先驱。
