[Characterization and Source Apportionment of Atmospheric VOCs in Tianjin in 2019]

The characterization and source apportionment of atmospheric volatile organic compounds (VOCs) in Tianjin in 2019 were investigated based on high-resolution online monitoring data observed at an urban site in Tianjin. The results showed that the average annual concentration of VOCs was 48.9 μg·m^-3, and seasonal concentrations followed with winter (66.9 μg·m^-3) > autumn (47.9 μg·m^-3) > summer (42.0 μg·m^-3) > spring (34.6 μg·m^-3). The chemical compositions of the VOCs were alkanes, aromatics, alkenes, and alkynes, which accounted for 65.0%, 17.4%, 14.6%, and 3.0% of the VOCs concentrations on average, respectively. The proportion of alkanes, aromatics, and alkynes was the highest in autumn, summer, and winter, respectively, while a higher alkenes proportion was observed in summer and winter. The ozone formation potential contribution of alkanes, alkenes, aromatics, and alkynes in spring and summer was 16.9%, 48.6%, 33.5%, and 1.0%, respectively, and the species with higher contributions were ethene, propylene, m,p-xylene, 1,2,3-trimethylbenzene, toluene, isoprene, trans-2-butene, cis-2-pentene, o-xylene, and m-ethyltoluene. During autumn and winter, the aromatics contributed as much as 91.5% to the secondary organic aerosol (SOA) formation potential, and o-xylene, toluene, m,p-xylene, ethylbenzene, o-ethyltoluene, and benzene were the main contributing species. Positive matrix factorization was applied to estimate VOCs source contributions, and automobile exhaust, liquefied petroleum gas/natural gas (LPG/NG) and gasoline evaporation, solvent usage, petrochemical industrial emissions, combustion, and natural sources were identified as major sources of VOCs in spring and summer, accounting for 29.2%, 19.9%, 16.4%, 10.3%, 7.3%, and 6.6%, respectively. While in autumn and winter, the contributions of LPG/NG and gasoline evaporation, automobile exhaust, combustion, solvent usage, and petrochemical industrial emissions were 32.4%, 21.9%, 18.5%, 13.3%, and 8.4%, respectively. Compared to the source contributions in spring and summer, a significant increase was observed for LPG/NG and combustion emission of 62.8% and 153.4%, respectively, and other sources decreased by 18.4%-25.0% in autumn and winter. Source composition spectrums showed that the petrochemical industry and solvent usage were the main emission sources of alkenes and aromatics in spring and summer, and combustion and solvent usage were the main emission sources of aromatics in autumn and winter. Thus, focus should be played on the petrochemical industry and solvent usage in spring and summer and on combustion and solvent usage in autumn and winter to further prevent and control ozone and SOA in Tianjin.