新冠疫情影响下全球对流层臭氧变化特征研究进展

Progress of Research on Global Tropospheric Ozone Variation Characteristics during COVID-19 Pandemic

自2020年新冠疫情(COVID-19)爆发以来,各地进行了不同程度的人员流动限制或封控,致使全球范围内氮氧化物(NO_(x))、二氧化硫(SO_(2))、一氧化氮(CO)、细颗粒物(PM2.5)等大气污染物浓度均大幅度降低,而作为二次污染物的臭氧(O_(3))在各地区却表现出复杂的变化特征,成为研究热点.本研究总结了近两年该方向的研究成果,阐明了COVID-19期间对流层O_(3)及其前体物的变化特征、变化机制及其可能存在的潜在环境效应.COVID-19严控期,全球人为NO_(x)排放下量降了至少15%,特别是高人为活动影响区,下降了18%-25%,部分高污染地区(挥发性有机物敏感区)近地层NO_(x)的减少量达50%以上.NO_(x)的减少导致NO对O_(3)的滴定作用减弱,使得该类高污染地区O_(3)增加(10%-50%).而偏远地区及自由对流层O_(3)主要受NO_(x)控制,NO_(x)的减少以及区域传输作用使得偏远地区及自由对流层O_(3)呈现减少状态.其中,2020年4月和5月,由于NO_(x)排放量的减少导致自由对流层O_(3)体积混合比减少量高达10×10^(-9);2020年5月和6月,全球对流层O_(3)总量下降了约6 Tg(O_(3))(-2%),亚洲和美洲NO_(x)排放量的减少对全球对流层O_(3)减少具有重要贡献.疫情严控期,NO_(x)浓度大幅度下降的情况下,我国大部分城市近地面O_(3)仍处于增加状态,这表明控制我国城市地区近地面O_(3)浓度的有效手段是根据O_(3)化学生成敏感区来控制前体物,但O_(3)前体物的剧烈变化也可改变O_(3)化学生成敏感区,导致O_(3)生成效率(OPE)的变化,但由于相对欠缺VOCs排放量及其大气浓度的观测,各地区O_(3)的变化趋势和主控因素还存在很大的不确定性.此外,未来COVID-19疫情和全球变暖叠加背景下,不同地区O_(3)的变化特征和对应的O_(3)调控策略亦值得进一步深入探究.

Restriction measures against coronavirus disease 2019(COVID-19)caused atmospheric trace species to change,especially in relation to air pollution.This severe pollutant emission reduction phenomenon during the pandemic led to intensive studies on its behavior.Most studies evidence a decrease in all pollutants except for O_(3).However,is this highlighted O_(3) trend a global trend?This study summarized the research results in the past two years and explored the characteristics,mechanisms,and potential environmental effects of tropospheric O_(3) and its precursors during the COVID-19 pandemic.During lockdown periods,global anthropogenic NO_(x) emissions decreased by at least 15%;especially,those in high-anthropogenic areas decreased by 18%-25%.In some highly polluted areas[volatile organic compound(VOC)-sensitive areas],NO_(x) emissions on the ground decreased by more than 50%.NO_(x) reduction led to the weakened titration effect of NO on O_(3),leading to an increase in O_(3) in such highly polluted areas(10%-50%).However,O_(3) in remote areas and free troposphere(NO_(x)-sensitive areas)decreased,attributed to NO_(x) reduction and regional transmission effect.During the strict control period of the pandemic,surface O_(3) was still increasing in most cities in China with significantly decreased NO_(x) concentration,indicating that the effective way to control surface O_(3) concentration in urban areas in China is controlling O_(3) precursors based on the sensitive area of O_(3) chemical generation.However,the drastic change in NO_(x) in each region could change the sensitive area of O_(3) chemical generation,leading to a change in O_(3) production efficiency.However,due to the lack of VOC emission measurement and their atmospheric concentration,there are still great uncertainties in the trend and main controlling factors of O_(3) in each region.In the future,the characteristics of O_(3) in different regions and corresponding O_(3) regulation strategies influenced by COVID-19 and global warming are also worthy of further study.