The Pollution Characteristics Of Volatile Organic Compounds Of The Typical Petrochemical Industry City In Northwest China

With the advancement of industrialization and urbanization,many cities in China are currently facing the dual pressure of fine particulate matter(PM_2.5)and ozone（O₃）pollution.As the common precursor of PM_2.5and O₃,volatile organic compounds（VOCs）have gradually become the focus of attention.The petrochemical industry is an important source of anthropogenic VOCs emissions in China.Lanzhou City and Qingyang City are typical petrochemical industry cities in northwest China.At present,the total amount and industry distribution of anthropogenic volatile organic compounds are unclear.The concentration,source and environmental effect of VOCs in ambient air are still indistinct in the normal production and maintenance stage of petrochemical enterprises,and pollution characteristics in different functional areas of petrochemical industry cities cannot be quantitatively mastered.In view of this,The continuous online monitoring is carried out by using of the Integrated Atmospheric Mobile Monitoring Vehicle（IAMMV）and the second survey of pollution sources.OBM model was used to analyze the causes of ozone pollution,positive matrix factorization（PMF）and ART-2a were used to analyze pollution sources.The main research conclusions are as follows:Through data review and field investigation on VOCs emission levels and related parameters of key industries in Lanzhou and Qingyang,it was calculated that the total anthropogenic volatile organic compounds（AVOCs）emissions of Lanzhou in 2019were 94761.6 t.Among them,non-industrial solvent source（52692.0t）,road mobile source（15911.6t）and oil storage source（7606.6t）had the largest VOCs emissions.AVOCs emissions of Lanzhou in 2019 were calculated to be 94761.6t.Among emission sources,Industrial solvent（52692.0t）,road mobile source（15911.6t）and oil storage source（7606.6t）VOCs emissions were the largest.The total AVOCs emission of Qingyang in 2019 was 18078.7 t,and the road mobile source（8209.2t）emitted the most.Based on the single particle aerosol mass spectrometer（SPAMS）,the localized single particle source spectra of different emission sources in Lanzhou were established,which laid the foundation for particle source and secondary organic aerosol（SOA）analysis.In order to study the pollution characteristics and change rules of VOCs in Xigu Industrial Zone of Lanzhou,the IAMMV was used to carry out continuous online monitoring research on Xigu district of Lanzhou from August 1 to August 28,2019,from August 7 to September 28,2020 and from September 16 to October 23,2022,respectively.During the monitoring period,VOCs concentration in 2019,2020 and2022 was 146.49ppb,92.84ppb and 61.74ppb,respectively,showing a decreasing trend year by year.Alkane concentration was the highest,followed by aromatic hydrocarbon in 2019,alkene in 2020 and 2022,and alkene concentration showed several sudden increases at night.Since 2020,alkene such as propylene and ethylene have contributed more to O₃generation.AVOCs are the most sensitive to O₃generation.ethylene and propylene should be closely paid attention to in VOCs management in Xigu.Using PMF to analyze the pollution sources of VOCs,the contribution of oil volatile sources and petrochemical process sources increased to25.7%and 16.1%respectively in 2020 compared with 2019.In 2022,compared with2020,the contribution of oil volatile sources（20.6%）and combustion sources（17.5%）decreased.Combined with the monitoring results of VOCs and SPAMS,the differences of air pollution characteristics between Xigu（industrial area,XG）and Chengguan（commercial and residential area,CG）in Lanzhou were discussed from multiple perspectives..During the monitoring period,the average concentration of ambient air VOCs in XG and CG monitoring points were 102.3ppb and 35.8ppb,respectively.The hourly concentration of VOCs varied widely,with several sudden increases at night in XG.alkene concentration（30.20ppb）and component ratio（29.41%）in XG were higher than those in Chengguan（3.78ppb,9.33%）.At XG and CG monitoring sites,the number of particles containing C₂H₃O⁺accounted for 36.96%and 15.41%of the total particles,respectively.The mixing ratio of OC and ECOC to C₂H₃O⁺at XG monitoring site reached 0.81 and 0.53,while that of CG was only 0.48 and 0.25.The atmosphere is heavily polluted by VOCs and SOA.The results of this study provide technical support for government departments to implement pollution control in different functional areas.The IAMMV was used to carry out continuous observation during the period of normal production（PⅠ）,partial overhaul（PⅡ）,and large-scale overhaul（PⅢ）of Petrochemical Enterprise A（PEA）in Qingyang.The results show that the VOCs concentration in the three period were 70.43,42.68 and 27.95ppb,respectively,and the alkane concentration decreased from 56.77ppb in PⅠ to 18.17ppb in PⅢ.From PⅠ to PⅢ,the OFP were 249.28,212.57 and 114.23μg/m³,respectively.At the same time,OFP/TVOC（4.98,4.09）of PⅡ and PⅢ were higher than that of PⅠ（3.54）,and the photochemical activity of PⅡ VOCs was the strongest.AVOCs at different period were most sensitive to O₃formation,The effect of NO_xreduction on ozone generation gradually decreased at PⅡ and PⅢ.The contribution of oil volatile sources in the three period was high.The storage and transportation of crude oil and products should be the key control objects.Meanwhile,PⅠ pays attention to the emission of combustion sources such as petroleum refining,and PⅢ pays attention to the contribution of solvent use.In government control,attention should be paid to the impact of VOCs emissions on O₃generation during overhaul of petrochemical enterprises.