Significant contribution of spring northwest transport to volatile organic compounds in Beijing

High values of ozone (O₃) occur frequently in the dry spring season; thus, understanding the evolution characteristics of volatile organic compounds (VOCs) in spring is of great significance for preventing O₃ pollution. In this study, a total of 101 VOCs from April 16 to May 21, 2019, were quantified using an online gas chromatography mass spectrometer/flame ionization detector (GCMS/FID). The results indicated that the observed concentration of total VOCs (TVOCs) was 30.4 ± 17.0 ppbv, and it was dominated by alkanes (44.3%), followed by oxygenated VOCs (OVOCs) (17.4%), halocarbons (12.7%), aromatics (9.5%), alkenes (8.2%), acetylene (5.3%) and carbon disulfide (2.5%). The average mixing ratio of VOCs showed obvious diurnal variation (high at night, low during daytime). We conducted a source apportionment study based on 32 major VOCs using positive matrix factorization (PMF), and coal + biomass burning (25.2%), diesel exhaust (16.0%), gasoline exhaust + evaporation (17.4%), secondary + long-lived species (16.7%), biogenic sources (4.3%), industrial emissions (9.3%) and solvent use (11.2%) were identified as major sources of VOCs. In addition to local emissions, most of the atmospheric VOCs were derived from long-distance air masses (65.7%), and the average mixing ratio of VOCs in the northwest direction was 29.4 ppbv. Combined with the results of the potential source contribution function (PSCF) indicate that research should focus on the local emissions of combustion, transportation sources and solvents usage to control atmospheric VOCs. Additionally, transmission of the northwest air mass is an important component that cannot be ignored during spring in Beijing.