COVID-19疫情对中国城市PM2.5的短期影响

Short-term Impacts of COVID-19 on PM_(2.5)in Urban China

为评估COVID-19疫情对中国城市PM2.5的影响,综合经验模态分解法和时变双重差分法,本文构建重大事件对空气污染影响多尺度评估模型。该模型能有效地将短期随机波动与长期趋势和事件冲击区分,进而更准确评估重大事件对于空气污染的影响。以2018年11月—2020年5月295个中国地级以上城市PM2.5日均浓度和气象信息数据集为研究样本,研究结果表明:COVID-19疫情出现导致196个城市PM2.5产生了结构性变化,并且不同城市对COVID-19疫情的响应效率不同。COVID-19疫情期间中国295个地级以上城市中155个城市PM2.5浓度显著下降10.66μg/m3,这很大程度上归因于中国城市封控政策。与未“封城”城市相比,实施“封城”政策的城市PM2.5浓度平均下降7.4497μg/m3,且不同城市区域差异明显。“封城”对中国城市PM2.5污染的改善效应是一种短期效应。政府的政策干预短期内改善了PM2.5污染程度,但同时付出了巨大的经济代价。因此,政府应采取更可持续性的措施来解决环境污染问题。

This paper quantifies environmental impact of extreme event in urban China by integrating empirical mode decomposition(EMD)with time-varying difference-in-differences(DID)approach.Our approach allows us to separate short-term random fluctuation from long-term trend and event shock,and thus improves the precision of the subsequent impact estimation.Using data on the daily PM_(2.5)concentrations and climate variations in 295 cities at the prefectural level from November 2018 to May 2020,the results show that the outbreak of COVID-19 caused structural changes of PM_(2.5)in 196 cities,and the response efficiencies across cities varied greatly.During the COVID-19 period,a significant decline of PM_(2.5)concentrations by 10.66μg/m~3 in 155 out of 295 cities,largely attributable to the city level lockdown.Compared with unlocked cities,PM_(2.5)dropped by 7.45μg/m~3 on average in cities with lockdown policy,with significant regional variations.Lockdown plays a short-term effect on the improvement of PM_(2.5)in Chinese cities.The temporary air quality improvement is achieved at tremendous economic cost.Therefore,governments shall address environmental pollution with more sustainable measures rather than city lockdown.