Heavy haze pollution during the COVID-19 lockdown in the Beijing-Tianjin-Hebei region, China

To investigate the characteristics of particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5) and its chemical compositions in the Beijing-Tianjin-Hebei (BTH) region of China during the novel coronavirus disease (COVID-19) lockdown, the ground-based data of PM_2.5, trace gases, water-soluble inorganic ions, and organic and elemental carbon were analyzed in three typical cities (Beijing, Tianjin, and Baoding) in the BTH region of China from 5-15 February 2020. The PM_2.5 source apportionment was established by combining the weather research and forecasting model and comprehensive air quality model with extensions (WRF-CAMx). The results showed that the maximum daily PM_2.5 concentration reached the heavy pollution level (>150 μg/m³) in the above three cities. The sum concentration of SO₄²⁻, NO₃⁻ and NH₄⁺ played a dominant position in PM_2.5 chemical compositions of Beijing, Tianjin, and Baoding; secondary transformation of gaseous pollutants contributed significantly to PM_2.5 generation, and the secondary transformation was enhanced as the increased PM_2.5 concentrations. The results of WRF-CAMx showed obviously inter-transport of PM_2.5 in the BTH region; the contribution of transportation source decreased significantly than previous reports in Beijing, Tianjin, and Baoding during the COVID-19 lockdown; but the contribution of industrial and residential emission sources increased significantly with the increase of PM_2.5 concentration, and industry emission sources contributed the most to PM_2.5 concentrations. Therefore, control policies should be devoted to reducing industrial emissions and regional joint control strategies to mitigate haze pollution.     

Variability of PM2.5 and O3 concentrations and their driving forces over Chinese megacities during 2018-2020

Recently,air pollution especially?ne particulate matters (PM_2.5) and ozone (O₃) has become a severe issue in China.In this study,we?rst characterized the temporal trends of PM_2.5and O₃for Beijing,Guangzhou,Shanghai,and Wuhan respectively during 2018-2020.The annual mean PM_2.5has decreased by 7.82%-33.92%,while O₃concentration showed insigni?cant variations by-6.77%-4.65%during 2018-2020.The generalized additive models (GAMs) were ...     

疫情期间人为源减排对城市大气氧化性的影响

近年来,中国经济发达地区以细颗粒物（PM_2.5）和臭氧（O₃）共同引发的区域性复合型大气污染事件频发,大气氧化性（AOC）在其中发挥着重要作用.基于WRF-CMAQ模型,以2020年疫情管控期为案例探究人为源减排对AOC的影响,选取中国东部3个典型城市（石家庄、南京和广州）进行深入分析,量化排放变化及气象变化对氧化剂和AOC变化的贡献,探讨AOC变化对二次污染物生成的影响.结果表明,与2019年同期相比,2020年石家庄、南京和广州的城市平均AOC分别增加了60%、48.7%和12.6%;氧化剂臭氧、羟基自由基和硝酸根自由基的浓度均有不同程度的增加（1.6%~26.4%、14.8%~73.3%和37.9%~180%）.排放变化使3个城市AOC分别增加了0.06×10^-4、0.12×10^-4和0.33×10^-4 min^-1,气象变化导致石家庄和南京AOC增加（分别为20%和17.9%）,但在广州却相反（-9.3%）.增强的AOC导致氮氧化速率和挥发性有机物氧化速率升高,即促进了一次污染物向二次污染物的转化,并抵消了部分一次减排的影响,造成了管控期间二次污染物相对排放的非线性变化.     

珠三角典型城市COVID-19疫情封闭期间臭氧污染的放大效应研究

珠三角地区臭氧(O₃)已经逐步取代颗粒物成为主要大气污染物。对新型冠状病毒肺炎(COVID-19)疫情封闭期间珠三角城市背景污染效应(特别是对O₃的放大效应)进行了量化研究,发现PM_2.5和NO₂质量浓度均为工作日高于节假日,非疫情期高于疫情期。O₃质量浓度节假日高于工作日,其中疫情期节假日浓度最高。减排会增加低温高湿背景下O₃质量浓度,但会降低其极大值,并导致 O₃随温度和相对湿度的变化梯度减弱。疫情封闭期间异地输送对于局地O₃质量浓度的变化贡献突出。叠加疫情封闭影响的春节假期O₃质量浓度比节前工作日增加20.4%~41.7%,与一般年份特征相反,而NO₂降低65.3%~75.6%,降低程度强于一般年份。疫情封闭期春节期间O₃质量浓度比一般年份上升14.0%~25.9%,而NO₂质量浓度降低37.0%~54.5%。低湿晴好的天气为光化学反应提供有利条件,并且疫情封闭扩大了假期人为源减排规模,导致NO_x质量浓度进一步下降,使其对O₃的滴定效应减弱,同时静稳天气有利于O₃浓度的累积,导致局地O₃污染被逐步放大。     

嘉善冬季碳质气溶胶变化特征及其来源解析

利用2018年冬季（2018年12月至2019年2月）和2019年冬季（2019年12月至2020年2月）嘉兴市嘉善县善西超级站有机碳（OC）、元素碳（EC）及细颗粒物（PM_2.5）浓度数据分析嘉兴嘉善地区碳质气溶胶变化特征及潜在来源区域.结果表明,2018年和2019年冬季OC浓度分别为6.90μg·m^-3和5.63μg·m^-3,EC浓度分别为2.47μg·m^-3和1.57μg·m^-3,2019年冬季OC和EC浓度较2018年冬季降幅分别为18.4%和36.4%.利用Minimum R-squared （MRS）方法计算得到2018年和2019年冬季二次有机碳（SOC）分别为1.49μg·m^-3和1.97μg·m^-3,一次有机碳（POC）浓度分别为5.41μg·m^-3和3.66μg·m^-3,SOC在OC中占比呈上升趋势,上升31.1个百分点,POC占比变化则相反.值得注意的是,随着PM_2.5浓度升高,OC和EC浓度呈上升趋势,最高上升幅度分别为474.7%和408.2%,但在PM_2.5中占比却呈下降趋势,OC和EC占比下降幅度分别为6.5个百分点和2.4个百分点;POC对PM_2.5的贡献波动不大,仅在150μg·m^-3以上有明显降低趋势,SOC对PM_2.5的贡献先下降后上升.嘉兴OC和EC潜在源区主要为苏南地区、安徽东南部和浙江北部,且2019年冬季和2018年冬季相比,OC和EC的主要潜在源区贡献浓度分别下降2μg·m^-3和6μg·m^-3以上,且潜在源区高值区域变小.疫情前受机动车尾气排放和燃煤共同影响,春节和居家隔离期间,因交通管制等原因,机动车排放量减少,燃煤贡献占比上升.