Field-based evidence of changes in household PM2.5 and exposure during the 2020 national quarantine in China

Air pollution exposure depends not only on outdoor but also on indoor air quality and human activities. The outbreak of coronavirus in 2019 occurred close to the Spring Festival in China, when many rural-to-urban workers moved to their hometowns, resulting in increased household (HH) consumption of solid fuels for space heating in the rural north. In this study, field measurements of HH PM2.5 (particulate matter with an aerodynamic size <= 2.5 mu m) from a rural village were performed to evaluate changes in indoor, outdoor, and total exposure during the quarantine. Both indoor and outdoor PM2.5 were, as expected, higher during the heating period than during the non-heating period, resulting in much more exposure during the heating season. Indoor exposure accounted for up to 87% and 95% of the total PM2.5 exposure during the non-heating and heating periods, respectively. The contributions of indoor exposure associated with internal sources were 46% and 66%, respectively. Indoor coal combustion resulted in an increment of about 62 +/- 12 mu g m(-3) in indoor PM2.5 exposure. Due to the quarantine, the indoor-originated PM2.5 exposure increased by 4 mu g m(-3) compared to that during the heating period before the lockdown. In comparison with the exposure before the quarantine during the heating period, the outdoor exposure decreased by 5 mu g m(-3) during the quarantine, which was mainly attributable to much less time spent outdoors, although the outdoor PM2.5 levels increased from 86 +/- 49 mu g m(-3) to 104 +/- 85 mu g m(-3). However, the overall exposure increased by 13 mu g m(-3) during the quarantine, resulting from the changes in outdoor exposure (-5 mu g m(-3)), outdoor-originated indoor PM2.5 exposure (+9 mu g m(-3)), PM2.5 from indoor sources before the quarantine (+5 mu g m(-3)), and quarantine-induced indoor PM2.5 increments (+4 mu g m(-3)). The increase in air pollution exposure during quarantine deepened concerns about the issue of HH air pollution and the clean HH energy transition actions required to eliminate traditional solid fuels.