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Ambient volatile organic compounds (VOCs) were measured using an onlinesystem, gas chromatography–mass spectrometry/flame ionization detector(GC-MS/FID), in Beijing, China, before, during, and after Asia-PacificEconomic Cooperation (APEC) China 2014, when stringent air quality controlmeasures were implemented. Positive matrix factorization (PMF) was appliedto identify the major VOC contributing sources and their temporalvariations. The secondary organic aerosols potential (SOAP) approach wasused to estimate variations of precursor source contributions to SOAformation. The average VOC mixing ratios during the three periods were86.17, 48.28, and 72.97 ppbv, respectively. The mixing ratios of total VOCduring the control period were reduced by 44 %, and the mixing ratios ofacetonitrile, halocarbons, oxygenated VOCs (OVOCs), aromatics, acetylene,alkanes, and alkenes decreased by approximately 65, 62, 54,53, 37, 36, and 23 %, respectively. The mixing ratios of allmeasured VOC species decreased during control, and the most affected specieswere chlorinated VOCs (chloroethane, 1,1-dichloroethylene, chlorobenzene).PMF analysis indicated eight major sources of ambient VOCs, and emissionsfrom target control sources were clearly reduced during the control period.Compared with the values before control, contributions of vehicular exhaustwere most reduced, followed by industrial manufacturing and solventutilization. Reductions of these three sources were responsible for 50,26, and 16 % of the reductions in ambient VOCs. Contributions ofevaporated or liquid gasoline and industrial chemical feedstock wereslightly reduced, and contributions of secondary and long-lived species wererelatively stable. Due to central heating, emissions from fuel combustionkept on increasing during the whole campaign; because of weak control ofliquid petroleum gas (LPG), the highest emissions of LPG occurred in thecontrol period. Vehicle-related sources were the most important precursorsources likely responsible for the reduction in SOA formation during thiscampaign

atmospheric chemistry and physics

Characterization of ambient volatile organic compounds and their sources in Beijing, before, during, and after Asia-Pacific Economic Cooperation China 2014