Huizhong Shen, Guofeng SHEN, Yilin Chen, Armistead Russell, Yongtao Hu, Xiaoli Duan, Wenjun Meng, Yang Xu, Xiao Yun, Baolei Lyu

The COVID-19 quarantine in China is thought to have been beneficial for reducing the population exposure to ambient air pollution. The overall exposure also depends, however, on indoor air quality and human mobility and activities, which also changed during the pandemic. Here we integrate real-time mobility data, questionnaire survey on during-pandemic human activity patterns, advanced air quality modeling techniques, and an indoor exposure model. We first show a decrease of 16.7 μg∙m-3 in the national average population-weighted ambient PM2.5 during the quarantine (i.e., the one month following the start of the Spring Festival holiday). The total population-weighted exposure (PWE) to PM2.5 considering both indoor and outdoor environments, however, increased by 5.7 μg∙m-3. The increase in PWE was mainly due to the nationwide population migration from urban to rural areas before the Spring Festival coupled with the freezing of the migration backward due to the quarantine (+10.8 μg∙m-3), which increased household energy consumption and the fraction of people exposed to rural household air pollution (HAP) indoors. The changes in PWE due to the quarantine were -14.0 and +19.2 ug∙m-3 among urban and rural populations, respectively, and ranged from -9.1 ug∙m-3 in the provinces with the highest per-capita income to 7.1 ug∙m-3 in the provinces with the lowest. HAP contributed 82% of PWE during this period, which was likely more severe than any period in recent years. Our analysis reveals an increased inequality of air pollution exposure during the COVID-19 quarantine and highlights the importance of HAP for population health in China.