Volatile organic compounds in wintertime North China Plain: Insights from measurements of proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS)

Min Shao , Xianjun He , Bin Yuan , Caihong Wu , Sihang Wang , Chaomin Wang , Yibo Huangfu , Jipeng Qi , Nan Ma , Wanyun Xu , Ming Wang , Wentai Chen , Hang Su , Yafang Cheng , Maofa Ge , Yujing Mu , Jianmin Chen , Zifa Wang


Received May 29, 2021,Revised , Accepted August 04, 2021, Available online January 14, 2022

Volume 34,2022,Pages 98-114

The characteristics of wintertime volatile organic compounds (VOCs) in the North China Plain (NCP) region are complicated and remain obscure. VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a rural site in the NCP from November to December 2018. Uncalibrated ions measured by PTR-ToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector (GC-MS/FID). The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions, the secondary formation of oxygenated VOCs (OVOCs) is non-negligible in the wintertime, i.e., OVOCs accounts for 42% ± 7% in the total VOCs (151.3 ± 75.6 ppbV). We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes. The chemical changes of organic carbon in a pollution accumulation period were investigated, which suggests an essential role of fragmentation reactions for large, chemically reduced compounds during the heavy-polluted stage in wintertime pollution. The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of “coal to gas” strategies in curbing air pollutants. The high abundances of some key species (e.g. oxygenated aromatics) indicate the strong emissions of coal combustion in wintertime of NCP. The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.

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