The comprehensive fingerprints of VOCs from complex coking emissions and their temporal evolution in the atmosphere based on backward inference method

Abstract

Coking industries are an important source of volatile organic compounds (VOCs). Coking emissions are characterized by diverse emission points, species and intensities, leading to inconsistencies in emission profiles. This complexity complicates the accurate identification of coking-related pollutants in the atmosphere. To obtain a distinct VOC fingerprint from coking emissions, 57 VOCs were detected based on a comprehensive sampling campaign conducted at three strategically placed sites (one in an area with intensive coking activity and two downwind sites) and one control site. We found a positive correlation between the contribution of coking emissions to total VOCs (TVOCs) (between 10.4 % and 44.2 %) and the severity of VOC pollution (TVOC content ranging from 28.75 to 49.28 ppbv). Furthermore, increases in the contribution of coking emissions to TVOC content resulted in increases in the proportions of alkenes (from 10 % to 19 % in summer and 13 % to 20 % in autumn) and aromatics (from 6 % to 18 % in autumn) in TVOCs. Ethane, ethene, propene, benzene, toluene, and acetylene were identified as dominant VOC species in coking emissions. Their concentrations increased as coking activity increased and were highly prevalent in the coking source profile, as indicated by positive matrix factorization analysis. The ratio of benzene to toluene, alongside the relative proportions of benzene, toluene, and ethylbenzene and of ethane, propane, and ethene was effective diagnostic indicators for identifying coking sources. The PMF-resolved factor profile from our field campaign could accurately represent coking emissions. Photochemical aging led to an underestimation of the coking-source contribution but had little effect on the ranges of the diagnostic indicators or the chemical profile of VOCs from coking sources.