ABSTRACT
A second wave of coronavirus disease 2019 (COVID-19) infections emerged in Beijing in summer 2020, which provided an opportunity to explore the response of air pollution to reduced human activity. Proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) coupled with positive matrix factorization (PMF) source apportionment were applied to evaluate the pollution pattern and capture the detailed dynamic emission characteristics of volatile organic compounds (VOCs) during the representative period, with the occurrence of O-3 pollution episodes and the Beijing resurgence of COVID-19. The level of anthropogenic VOC was lower than during the same period in previous years due to the pandemic and emission reduction measures. More than two thirds of the days during the observation period were identified as high-O-3 days and VOCs exhibited higher mixing ratios and faster consumption rates in the daytime on high-O-3 days. The identified VOC emission sources and the corresponding contributions during the whole observation period included: vehicle + fuel (12.41 +/- 9.43%), industrial process (9.40 +/- 8.65%), solvent usage (19.58 +/- 13.46%), biogenic (6.03 +/- 5.40%), background + long-lived (5.62 +/- 11.37%), and two groups of oxygenated VOC (OVOC) factors (primary emission and secondary formation, 26.14 +/- 15.20% and 20.84 +/- 14.0%, respectively). Refined dynamic source apportionment results show that the 'stay at home' tendency led to decreased emission (-34.47 +/- 1.90%) and a weakened morning peak of vehicle + fuel during the Beijing resurgence. However, a growing emission of primary OVOCs (+51.10 +/- 8.28%) with similar diurnal variation was observed in the new outbreak and afterwards, which might be related to the enhanced usage of products intended to clean and disinfect. The present study illustrated that more stringent VOC reduction measures towards pandemic products should be carried out to achieve the balanced emission abatement of NO (x) and VOC when adhering to regular epidemic prevention and control measures.