*2.1. Study Region*

This study focuses on COVID-19 s footprint on air quality in 15 cities of China's mainland namely Guangzhou, Xiamen, Xian, Wuhan, Beijing, Nanjing, Xinjiang, Lanzhou, Anshan, Shanghai, Jinan, Harbin, Chongqing, Zhengzhou, and Chengdu from where 145 random grid samples were taken for micro-level assessment with the help of air quality zonal modeling (Figures 3 and 6).
