2020～2021年新冠疫情期间南京市PM2.5化学组成与来源变化特征

为了解新冠疫情期间极端减排情景下南京市PM_2.5的化学组成和来源变化，对南京市2020年1～3月和2021年6～8月两次疫情管控前后PM_2.5化学组分(水溶性无机离子、碳质组分和无机元素)的小时观测结果进行分析.结果表明，NO^-₃浓度在两次疫情管控期间比管控前分别下降52.9%和43.0%,高于NH⁺₄(46.4%和31.6%)和SO₄^2-(33.8%和16.5%).由于观测点位于交通干道附近，元素碳(EC)的下降幅度(35.4%和20.6%)高于有机碳(OC; 11.1%和16.2%).结合以上丰量组分特征比值的变化，推断疫情管控对交通排放的影响比工业活动更显著.各主要丰量组分浓度在疫情管控前后的连续变化过程表明，来自本地交通排放的NO_x对PM_2.5中NO^-₃的形成有重要贡献，并且是短期内本地PM_2.5...

Variations in PM2.5 Composition and Sources During 2020-2021 COVID-19 Epidemic Periods in Nanjing

To understand the changes in chemical composition and sources of PM_2.5 under the extreme reduction background during the COVID-19 epidemic periods in Nanjing, hourly observation results of PM_2.5 components (water-soluble inorganic ions, carbonaceous components, and inorganic elements) of two epidemic events from January to March 2020 and June to August 2021 were analyzed. In comparison to that during pre-epidemic periods, the concentration of NO₃^- during the two epidemic control periods decreased by 52.9% and 43.0%, respectively, which was larger than the decreases in NH₄⁺(46.4% and 31.6%) and SO₄^2-(33.8% and 16.5%). Since the observation site was located close to a main road, the decrease in elemental carbon (EC, 35.4% and 20.6%) was higher than that in organic carbon (OC, 11.1% and 16.2%). In reference to the variations in the characteristic ratios of the bulk components mentioned above, the epidemic control showed a more substantial influence on traffic emissions than industrial activities. The concentration time series of PM_2.5 major components over the epidemic periods indicated that NO_x from local traffic emissions had substantial contributions to the formation of NO₃^-, which led to local short-term PM_2.5 pollution. In addition, the positive matrix factorization (PMF) model was used to analyze the hourly observation data of PM_2.5 components. The seven identified factors were linked with metallurgy, firework and firecracker combustions, road traffic emissions, coal combustion, dust resuspension, secondary sulfate, and secondary nitrate. Because the nitrate was unstable under high temperature, the contribution of secondary nitrate to PM_2.5 during the epidemic control period of 2021 (summer, 21.2%) was much lower than that during the epidemic control period of 2020 (winter, 60.6%); however, the formation of secondary components always dominated the contribution of PM_2.5 sources. Therefore, emissions of NO_x and SO₂ should be further controlled to continuously reduce ambient PM_2.5 concentrations in Chinese cities.