Characteristics, sources and regional inter-transport of ambient volatile organic compounds in a city located downwind of several large coke production bases in China

Abstract

Abstract Volatile organic compounds (VOCs) are important precursors of atmospheric ozone (O3) and particulate matter (PM). Taiyuan, located downwind of several large coke production bases, is a heavily polluted city in China, with high concentrations of PM and increasing concentrations of ground-level O3. In this study, 116 air samples were collected in four seasons of 2015 and analyzed for non-methane hydrocarbon and halocarbon species. The annual average concentration of the total VOCs (TVOCs) in Taiyuan was observed to be higher and slightly lower than that in Beijing and Shenzhen, respectively. High concentrations of benzene and a high benzene to toluene (B/T) ratio were the most evident features. TVOCs levels showed significant seasonal variations, increasing from spring (31.08 ppbv) to winter (67.33 ppbv). Although the concentrations of many air pollutants declined to a minimum, TVOCs continued to show high levels during the summer. Six sources were resolved using positive matrix factorization (PMF), and results indicated that coking processes was the largest contributor (32.56%) to ambient VOCs in Taiyuan, followed by coal and biomass combustion (23.25%). In winter, the contributions of combustion sources and liquefied petroleum gas/natural gas/coalbed methane (LPG/NG/CBM) usage significantly increased compared with those in other seasons. The coking bases located upwind of Taiyuan in the southwestern and western directions were the major potential source regions of coking related VOCs, as indicated using the potential source contribution function (PSCF) analysis. More than 70%, 40% and 80% of the air masses were transported from Taiyuan to the Beijing-Tianjin-Hebei (BTH) region during spring, autumn and winter, respectively. This study indicated that the coke production bases in Shanxi should be listed as the key regions to address the air pollution problems throughout north China. In addition, the combustion source in Taiyuan was associated with high local emissions, while Hebei province located in the northeastern direction, Shaanxi and Inner Mongolia located in the northwestern direction were the potential sources of solvent and LPG/NG/CBM usage, respectively.