To prevent the spread of COVID-19 (2019 novel coronavirus), from January 23 to April 8 in 2020, the highest Class 1 Response was ordered in Wuhan, requiring all residents to stay at home unless absolutely necessary. This action was implemented to cut down all unnecessary human activities, including industry, agriculture and transportation. Reducing these activities to a very low level during these hard times meant that some unprecedented naturally occurring measures of controlling emissions were executed. Ironically, however, after these measures were implemented, ozone levels increased by 43.9%. Also worthy of note, PM_2.5 decreased 31.7%, which was found by comparing the observation data in Wuhan during the epidemic from 8th Feb. to 8th Apr. in 2020 with the same periods in 2019. Utilizing CMAQ (The Community Multiscale Air Quality modeling system), this article investigated the reason for these phenomena based on four sets of numerical simulations with different schemes of emission reduction. Comparing the four sets of simulations with observation, it was deduced that the emissions should decrease to approximately 20% from the typical industrial output, and 10% from agriculture and transportation sources, attributed to the COVID-19 lockdown in Wuhan. More importantly, through the CMAQ process analysis, this study quantitatively analyzed differences of the physical and chemical processes that were affected by the COVID-19 lockdown. It then examined the differences of the COVID-19 lockdown impact and determined the physical and chemical processes between when the pollution increased and decreased, determining the most affected period of the day. As a result, this paper found that (1) PM_2.5 decreased mainly due to the reduction of emission and the contrary contribution of aerosol processes. The North-East wind was also in favor of the decreasing of PM_2.5. (2) O₃ increased mainly due to the slowing down of chemical consumption processes, which made the concentration change of O₃ pollution higher at about 4 p.m.–7 p.m. of the day, while increasing the concentration of O₃ at night during the COVID-19 lockdown in Wuhan. The higher O₃ concentration in the North-East of the main urban area also contributed to the increasing of O₃ with unfavorable wind direction.

为防止 COVID-19（2019 年新型冠状病毒）的传播，从 2020 年 1 月 23 日至 4 月 8 日，武汉市实施了最高一级响应，要求所有居民除非绝对必要，否则不得外出。实施这一行动是为了减少一切不必要的人类活动，包括工业、农业和交通运输。在这些困难时期将这些活动减少到非常低的水平意味着执行了一些前所未有的自然发生的控制排放的措施。然而具有讽刺意味的是，在这些措施实施后，臭氧水平却上升了 43.9%。同样值得注意的是，PM _2.5武汉市2020年2月8日至4月8日疫情期间的观测数据与2019年同期相比下降31.7%。利用CMAQ（社区多尺度空气质量建模系统），本文调查了这些现象的原因基于四组不同减排方案的数值模拟。将四组模拟与观察进行比较，推断出由于武汉 COVID-19 封锁，典型工业产出的排放量应减少至约 20%，农业和交通来源的排放量应减少 10%。更重要的是，通过 CMAQ 过程分析，本研究定量分析了受 COVID-19 封锁影响的物理和化学过程的差异。然后，它检查了 COVID-19 锁定影响的差异，并确定了污染增加和减少之间的物理和化学过程，从而确定了一天中受影响最大的时段。结果，本文发现（1）PM_2.5减少主要是由于排放减少和气溶胶过程的相反贡献。东北风也有利于PM _2.5的降低。（2）O ₃增加主要是由于化学消耗过程的放缓，使得O ₃污染浓度在白天4点到7点左右变化较大，而在COVID期间夜间O ₃浓度增加-19 武汉封城。主城区东北部O _{3浓度较高也导致O 3}增加，风向不利。