Characterization and sources of volatile organic compounds (VOCs) and their related changes during ozone pollution days in 2016 in Beijing, China

Concentrations of 99 volatile organic compounds (VOCs) were continuously measured online at an urban site in Beijing, China, in January, April, July, and October 2016. Characterization and sources of VOCs and their related changes during days with heavy ozone (O₃) pollution were analysed. The total observed concentration of VOCs (TVOCs) was 44.0 ± 28.9 ppbv. The VOC pollution level has decreased in Beijing but remains higher than in other Chinese cities. Alkanes comprised the highest proportion among seven major sampled VOC groups. The concentrations and sources of ambient VOCs showed obvious temporal variations. Six emission sources were identified by the positive matrix factorization (PMF), including biomass burning, coal combustion, gasoline vehicles, diesel vehicles, solvent usage, and biogenic + secondary emissions. The combustion source was the key control factor for VOC reduction in Beijing. From the potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) model, Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia, Shandong, and Henan were identified as major potential source regions of ambient VOCs. O₃ formation was sensitive to VOCs in Beijing according to the VOC/NOx ratio (ppbC/ppbv, 8:1 threshold). High- and low-O₃ days in July were identified, and high O₃ levels were due to both enhanced VOC emission levels and meteorological conditions favourable to the production of O₃. These findings provide evidence that the fuel combustion and regional transport have a great impact on concentrations and sources of VOCs in urban Beijing.