The year-round variations of VOC mixing ratios and their sources in Kuytun City (northwestern China), near oilfields

Abstract

Few studies of volatile organic compounds (VOCs) near oilfields have been performed. Continuous online measurements of 102 VOC species were made for 1 year in Kuytun city (northwestern China), near the Karamay and Tuha oilfields. The total VOC (TVOC) concentrations were high (mean 45.6 ppbv, range 21.9–86.1 ppbv). Alkanes, alkenes, nitrogen- and oxygen-containing VOCs, acetylene, halohydrocarbons, and aromatic compounds contributed 46.6%, 23.7%, 12.9%, 11.8%, 11.4%, and 5.3%, respectively, of TVOC concentrations. TVOC concentration varied markedly by season, and decreased in the order winter, spring, summer, fall. The dominant 11 VOCs (in decreasing concentration order) were acetylene, ethane, propane, carbon tetrachloride, isopentane, ethylene, n-butane, acetone, isobutane, methyl tert-butyl ether, and n-pentane, which contributed 68% of TVOC concentrations. The acetone, acetylene, chloroethylene, ethane, ethylene and benzene concentrations were higher on more-polluted than less-polluted days but the n-butane, carbon tetrachloride, isobutane, isopentane, methyl tert-butyl ether, n-pentane, and propane concentrations were always lower on more-polluted than less-polluted days. A positive matrix factorization model indicated that acetylene was the main VOC emitted through combustion during the heating period but acetylene, halohydrocarbons, and oxygen-containing VOCs emitted by industrial plants were dominant during the non-heating period. Carbon tetrachloride, methyl tert-butyl ether, and propane were the dominant VOCs emitted by petrochemical plants, gasoline-powered vehicles and liquefied petroleum gas, respectively. Air mass back trajectories (72 h) indicated that VOCs were mainly supplied by local and regional sources but clean air from Kazakhstan decreased VOC concentrations when wind came from the northwest at wind speeds higher than scale 5.