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Volatile organic compounds (VOCs) play an important role in the formation of ozone. The concentrations of VOCs in the Jinnan District of Tianjin were monitored by the Syntech Spectras GC955 online monitoring system, and the ozone generation potential of VOCs was calculated by the maximum incremental activity factor. The results showed that the total concentration of VOCs in the Jinnan District was (32.33±23.77) μg·m -3 , in which the mass concentration of alkane was the highest, and propylene, ethylene and toluene had the highest mass concentration. During the observation period, the ozone formation potential (OFP) of TVOC was 107.81 μg·m -3 , and the contribution of alkenes to OFP was the largest, which was 55.80%. Ethylene, isoprene, and toluene accounted for the first three places of OFP contribution rate. The backward trajectory analysis showed that TVOC and its OFPs were different under different trajectories. The estimation of VOCs/NO x volume fraction ratio showed that O 3 formation was sensitive to VOCs, which showed that atmospheric photochemical pollution has a considerable degree of regional characteristics. The concentration ratio of ethylbenzene/ m,p -xylene, and ethane/acetylene can be used to measure the progress of atmospheric chemical reaction and photochemical age in the air mass, which was proved by the aging process of VOC.

Based on the online measurements of VOCs of high pollution process at the university site in winter, VOCs' characteristics and species at different levels of haze pollution were analyzed. Fifty-five VOCs were detected during sampling. ∑ 55 VOCs concentrations ranged between 25.5×10 -9 -1320.3×10 -9 (avg±SD,240×10 -9 ±181×10 -9 ). Toluene and xylene were the major pollutants during high pollution process, the concentrations of which were higher than those of industrial area. The university site shared a similar VOC composition with that of industrial area, which suggested that it might be influenced by the surrounding industries. VOCs species exhibited high concentrations in nighttime while low concentrations in daytime. The ozone concentrations were on the contrary. Aromatic hydrocarbons were predominant with a high percentage of contribution (70.0%) to OFP (ozone formation potential). Alkenes and alkynes were the second highest group (16.7%). The OFP of VOCs was 2078.2×10 -9 under the west-south wind direction, about 4 times higher than the value under other wind directions (505.8×10 -9 ). Aromatic hydrocarbons exhibited a predominant contribution to OFP at different levels of haze pollution in this area, among which, Toluene and xylene contributed more than 50% to OFP. The newest version of EPA PMF model was used to identify the major source of VOCs and evaluate their contributions. Gasoline sources and vehicle exhaust, refinery and petroleum products, solvent use and organic synthetic materials were the identified VOC sources in the study area, contributing 33.1%, 31.5%, 30.5%, and 4.9%, respectively to the ∑ 55 VOCs concentrations.