Oxygenated volatile organic compounds in Beijing: Characteristics, chemical reactivity, and source identification

As important components of volatile organic compounds (VOCs), oxygenated VOCs (OVOCs) play a crucial role in the photochemical formation of ozone (O₃), especially in the polluted areas in the North China Plain (NCP). However, their seasonal characteristics and sources are not well understood. In this study, one-year measurements of 10 typical OVOCs were conducted through proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) at an urban site (39.95° N, 116.32° E, 96 m a.s.l.) in Beijing. Aldehydes and alcohols were the most abundant types of OVOCs in the entire year, with mean concentrations of 16.3 ppbv and 15.9 ppbv, respectively, and mean proportions of 33.8 % and 32.4 % of the total. Formaldehyde and ethanol sustained the highest concentrations throughout the year, with mean annual concentrations of 13.5 ppbv and 10.8 ppbv, respectively. The results indicated that the concentrations of OVOCs were highest in the summer, along with the maximum O₃-formation potentials and hydroxyl radical (•OH) reactivity values of 83.5 ppbv and 2.8 s^-1, respectively. Results from the source apportionment of OVOCs based on multiple linear regression models indicated that secondary productions were the predominant source in summer. In particular, the secondary sources of aldehydes represented by CH₂O and acetaldehyde accounted for 36.7 % and 51.4 % of the total, respectively. This study determined the concentrations and photochemical generation of OVOCs in different seasons, providing a basis for O₃ pollution control in urban areas of Beijing.