State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China.
State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China.
Environ Pollut. 2021 Jun 15;279:116923. doi: 10.1016/j.envpol.2021.116923. Epub 2021 Mar 10.
To control the spread of COVID-19, China implemented a series of lockdowns, limiting various offline interactions. This provided an opportunity to study the response of air quality to emissions control. By comparing the characteristics of pollution in the summers of 2019 and 2020, we found a significant decrease in gaseous pollutants in 2020. However, particle pollution in the summer of 2020 was more severe; PM levels increased from 35.8 to 44.7 μg m, and PM increased from 51.4 to 69.0 μg m from 2019 to 2020. The higher PM was caused by two sandstorm events on May 11 and June 3, 2020, while the higher PM was the result of enhanced secondary formation processes indicated by the higher sulfate oxidation rate (SOR) and nitrate oxidation rate (NOR) in 2020. Higher SOR and NOR were attributed mainly to higher relative humidity and stronger oxidizing capacity. Analysis of PM distribution showed that severe haze occurred when particles within Bin2 (size ranging 1-2.5 μm) dominated. SO and SO remained stable under different periods at 0.5 and 0.8, respectively, indicating that SO existed mainly in smaller particles. Decreases in NO and increases in NO from clean to polluted conditions, similar to the variations in PM distribution, suggest that NO played a role in the worsening of pollution. O concentrations were higher in 2020 (108.6 μg m) than in 2019 (96.8 μg m). Marked decreases in fresh NO alleviated the titration of O. Furthermore, the oxidation reaction of NO that produces NO was dominant over the photochemical reaction of NO that produces O, making NO less important for O pollution. In comparison, a lower VOC/NO ratio (less than 10) meant that Beijing is a VOC-limited area; this indicates that in order to alleviate O pollution in Beijing, emissions of VOCs should be controlled.
为控制 COVID-19 的传播，中国实施了一系列封锁措施，限制了各种线下互动。这为研究空气质量对排放控制的响应提供了机会。通过比较 2019 年和 2020 年夏季污染特征，我们发现 2020 年气态污染物显著减少。然而，2020 年夏季的颗粒物污染更为严重；PM2.5 浓度从 2019 年的 35.8μg/m3增加到 44.7μg/m3，PM10 从 51.4μg/m3增加到 69.0μg/m3。更高的 PM 是由 2020 年 5 月 11 日和 6 月 3 日的两次沙尘暴事件造成的，而更高的 PM 则是由于硫酸盐氧化率（SOR）和硝酸盐氧化率（NOR）更高表明 2020 年二次形成过程增强。更高的 SOR 和 NOR 主要归因于更高的相对湿度和更强的氧化能力。对 PM 分布的分析表明，当 Bin2（粒径 1-2.5μm）范围内的颗粒物占主导地位时，会发生严重的雾霾。在不同时期，SO2 和 SO4 的比例分别稳定在 0.5 和 0.8，表明 SO2 主要存在于较小的颗粒物中。NO 从清洁到污染条件的减少和 NO2 的增加与 PM 分布的变化相似，表明 NO 在污染恶化中起作用。2020 年的 O3浓度（108.6μg/m3）高于 2019 年（96.8μg/m3）。新鲜 NO 的大量减少缓解了 O3 的滴定。此外，产生 NO 的 NO 氧化反应占主导地位，而产生 O3 的 NO 光化学反应则不占主导地位，这使得 NO 对 O3 污染的重要性降低。相比之下，更低的 VOC/NO 比值（小于 10）意味着北京是一个 VOC 受限的地区；这表明为了缓解北京的 O3 污染，应该控制 VOCs 的排放。
