| Persistent and regional large-scale near surface ozone and fine particulate matter pollution is one of the most concerned problems in China’s environmental science community.As a kind of important precursors,VOCs participate in the photochemical formation of ozone and secondary organic aerosols.Improving the accurate and rapid monitoring ability has become a necessary means to further promote the monitoring and prevention of VOCs in China.Relying on the project of Zibo Ecological Environment Bureau of Ministry of ecological environment,four sets of continuous monitoring systems of VOCs in ambient air based on gas chromatography-mass spectrometry/hydrogen flame ionization detector(GC-MS/FID)were established.Taking 107 kinds of VOCs as target compounds,the comparison and application research of each system were carried out by analyzing different concentrations of PAMS and TO-15 mixed standard gases and monitoring the VOCs in the ambient air of Zibo High-tech Zone for seven consecutive days.The main research conclusions are as follows:(1)The composition and working principle of each system were basically the same,but the channel structure and separation mode of chromatographic column were slightly different,which determined that ZF system and AM system could achieve the cumulative sampling time of no less than 30 minutes per hour,while TT system and GM system could achieve the blind spot free sampling with the cumulative sampling time of 60 minutes per hour.(2)Each system had a certain monitoring ability for 107 kinds of VOCs,and its measurement range fully met the requirements of current domestic ambient air monitoring.There were some typical problems in each system: in ZF system,there was a certain systematic error in the MSD channel,the separation ability of gas chromatographic column was limited or the temperature program of the column oven was not optimized enough,the preconcentration analysis unit might have insufficient enrichment problems,and the gas circuit hardware also needed to be strengthened;in AM system,there was a large systematic error,and its FID detection performance for low concentration components was not very good;in TT system,the zero point noise of individual components needed to be further reduced,and its software needed to optimize the ability of accurately and automatically identifying mass spectrum peaks;in GM system,the stability needed to be further improved,and its working environment requirements were relatively harsh.(3)Pearson correlation was significant among the measured results of each system,but Bland-Altman analysis showed that only ZF system and GM system,AM system and GM system had significant consistency,and other groups had significant differences.The correlation among the concentrations of m,p-Xylene and o-Xylene monitored by each system was significant,but the slope of the fitting curve of m,p-Xylene and o-Xylene concentration of ZF system was quite different from that of other systems,which indicated that there were some defects in the monitoring ability of ZF system.(4)The average concentration of total VOCs in every system was 116.748 ± 63.079 ppbv,and the trend of each system was basically the same.By analyzing the characteristics of daily and weekly concentration of VOCs,it was found that atmospheric temperature and wind direction had a great influence on the concentration of total VOCs in Zibo High-tech Zone.Through the analysis of four times VOCs concentration fluctuations,it was found that Ethanol,Propane,Acetone and so on were the dominant components of VOCs in Zibo City and the reasons for the increase of VOCs were that the light rain weather led to poor diffusion conditions and affected the chemical reaction of VOCs in the ambient air,the southeast wind brought industrial waste gas from Linzi District and the north wind brought industrial waste gas rich in Benzene series from Huantai County.As a traditional industrial city,Zibo had a smaller characteristic ratio of m,p-Xylene to o-Xylene than other cities in China. |
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