Characteristics and sources of volatile organic compounds during pollution episodes and clean periods in the Beijing-Tianjin-Hebei region

Abstract

Volatile organic compounds (VOCs) play an important role in air pollution. In this study, we conducted comprehensive field observations to investigate wintertime air pollution in Beijing, Wangdu, and Dezhou in the Beijing-Tianjin-Hebei region during 2017 and 2018. The average VOC concentrations of the three sites were 35.6 ± 26.6, 70.9 ± 56.3, and 50.5 ± 40.0 ppbv, respectively. The species with the highest concentration were similar in all three sites and included ethane, ethylene, acetylene, acetone, and toluene. The VOC mixing ratios of the three sites showed synchronous growth during pollution episodes and were 1.2-2 times higher than those during clean periods. Moreover, the OH loss rates (L_OH) during pollution episodes were 1.2-1.7 times that during clean periods. The crucial reactive species in the three sites were ethylene, propylene, and acetaldehyde, contributing approximately 70% to the total L_OH during pollution periods. According to the source apportionment analysis, vehicle exhausts were the largest source of VOCs in Beijing, accounting for more than 50% of the total emissions. During the pollution episodes, Beijing's industrial emissions decreased, but the secondary and background sources increased. Coal combustion was significant (approximately 40%) in Wangdu and should therefore be prioritized in emission reduction policies. In Dezhou, industrial emissions had a considerable impact on the VOC mixing ratio during pollution periods and should therefore be prioritized. The backward trajectory analysis showed that VOCs from the southern region likely contribute to Beijing's VOC pollution, highlighting the importance of regional integration for air quality management.

Keywords: Beijing-Tianjin-Hebei (BTH) region; Pollution episodes; Source apportionment; Volatile organic compounds (VOCs).