Abstract：
Although COVID-19 lockdown policies have improved air quality in numerous countries, there is a lack of empirical evidence on the extent to which recovery has resulted in air pollution rebound, and the differences and similarities among regions\' recovery modes during the period of easing COVID-19 restrictions. Here, we used daily air quality data and the recovery index constructed by a city-pair inflow index for 119 cities in China to quantify the impact of recovery on air pollution from March 2 to October 30, 2020. Findings show that recovery has significantly increased air pollution. When the recovery level increased by 10 %, the concentration of PM2.5, SO2, and NO2 respectively deteriorated by 1.10, 0.33, 1.25 μg/m3, and the average growth rates of three air pollutants were about 3 %-6 %. Moreover, we used the counterfactual framework and time series clustering with wavelet transform to cluster the rebound trajectory of air pollution for 17 provinces into five recovery modes. Results show that COVID-19 has further intensified regional differentiations in economic development ability and green recovery trend. Three northwestern provinces dependent on their resource endowments belong to energy-intensive recovery mode, which have experienced a sharp rebound of air pollution for two months, thereby making green recovery more challenging to achieve. Three regions with a diversified industrial structure are in industrial-restructuring recovery mode, which has effectively returned to a normal level through adjusting industrial structure and technological innovation. Owing to local policies and the outbreak of COVID-19 in other countries, six provinces in policy-oriented and international trade-oriented recovery modes have not fully recovered to the level without COVID-19 until October 2020. The result highlights the importance of diversifying industrial structure, technological innovation, policy flexibility and industrial upgrading for different recovery modes to achieve long-term green recovery in the future.
摘要：
尽管COVID-19封锁政策改善了许多国家的空气质量，缺乏关于恢复在多大程度上导致空气污染反弹的经验证据，以及在放宽COVID-19限制期间，各地区恢复模式之间的差异和相似之处。这里,我们使用中国119个城市的每日空气质量数据和由城市对流入指数构建的恢复指数来量化2020年3月2日至10月30日恢复对空气污染的影响。研究结果表明，恢复显著增加了空气污染。当恢复水平增加10%时，PM2.5、SO2和NO2浓度分别下降1.10、0.33、1.25μg/m3,3种大气污染物的平均增长率约为3%-6%。此外，利用反事实框架和时间序列聚类结合小波变换,将17个省份的空气污染反弹轨迹聚类为5种恢复模式。结果表明，COVID-19在经济发展能力和绿色复苏趋势方面进一步加剧了区域差异。西北三省依靠其资源禀赋属于能源密集型回收模式,经历了两个月的空气污染急剧反弹，从而使绿色复苏更具挑战性。三个产业结构多元化的地区处于产业结构调整的复苏模式,通过调整产业结构和技术创新，已经有效地恢复到正常水平。由于当地的政策和其他国家爆发的COVID-19，在2020年10月之前，以政策为导向和以国际贸易为导向的复苏模式的六个省份尚未完全恢复到没有COVID-19的水平。结果凸显了产业结构多元化的重要性，技术创新,不同恢复模式的政策灵活性和产业升级，实现未来长期绿色恢复。
