| The sampling point of this paper was located in the urban area of Jinan.The Kostar mobile monitoring vehicle was used to monitor 107 VOCs online.The sampling period was May,September 2019,and November 2020.The concentration and pollution characteristics of VOCs in the ambient atmosphere were analyzed.Using the MCM mode combined with sensitivity experiments,the generation mechanism of ozone(O3)was studied,and the net ozone generation rate and the main photochemical reaction pathways were obtained.Combining the calculated values of Ozone Formation Potential(OFP)and Secondary Organic Aerosol Formation Potential(SOAp),the dominant species of VOCs that have a greater contribution to the production of O3and fine particulate matter(PM2.5)were identified.And compared with the monitored VOCs data surrounding areas of a petrochemical company during the same period,the impact of corporate stationary source was analyzed.Based on the VOCs data obtained by the VOCs navigating vehicle from a machining company around the sampling point in June 2019,the traceability analysis of the VOCs emitted by the machining company’s stationary sources was carried out.Also,the VOCs pollution control measures were proposed.The main conclusions are as follows:(1)From the perspective of the total amount of VOCs,the TVOC concentration in May2019 was higher than the other two monitoring periods,with the data 247.44μg/m~3.the concentration of VOCs in the three samplingperiods was dominated by oxygenated organics,with the highest proportion of oxygenated organics in September is 55.3%.There wer 6 species with the same concentration of the top ten in the three sampling periods,namely ethanol,acetone,para-xylene,benzene,dichloromethane and toluene,indicating that there was a fixed emission pollution source at this sampling point.The high concentration of VOCs in the morning and evening peak periods was related to vehicle exhaust emissions.The oxygenated volatile organic compounds presented a higher concentration at night and a lower change during the day.The variation of TVOC concentration was exactly opposite of the variationof O3 concentration,indicated that the participation of VOCs species.were related to photochemical reactions.In May and September 2019,when the O3 concentration exceeded the standard value,the top ten VOCs species had a larger concentration decrease compared to when the O3 concentration did not exceed the standard value.The species were ethanol and p-xylene,indicating that both of them were more effective for the O3 formation in May and September 2019.(2)According to the research on the potential of VOCs to generate ozone,it can be seen that the OFP value of aromatic hydrocarbons accounted for the highest proportion in the three sampling periods.The∑OFP value in May 2019 was the largestwith 951.17μg/m~3,and the OFP value of aromatic hydrocarbons reached to 554.86μg/m~3.Species that had a high contribution to ozone production wer mainly isoprene,ethanol,methyl methacrylate and aromatic hydrocarbon VOCs;In May and September 2019,among the top ten species with an OFP value when the O3concentration exceeded the standard value,the species with a greater decrease in OFP value than when the O3 concentration did not exceed the standard value were para-xylene,ortho-xylene,ethylbenzene,meta-ethyltoluene and Ethanol.Species with a greater reduction in ozone generation potential were para-m-xylene,o-xylene and ethanol.It showed that the generation of ozone in the two sampling periods was mainly affected by the active components such as para-m-xylene,o-xylene and ethanol.(3)The results of the MCM model showed that the photochemical generation of O3 during the sampling period in May 2019(30.20 ppb/h)was faster than that in September 2019(6.90ppb/h)and November 2020(3.95 ppb/h).O3 formation was mainly controlled by methylperoxy radicals(CH3O2)+NO and hydroxyperoxy radicals(HO2)+NO,and the net formation reaction rate had a peak at noon.A simulation the net O3 formation arounding a petrochemical company’s point during the same period in May 2019 showed that its average rate(17.91ppb/h)was lower than that of the sampling point’s average valuee(30.20ppb/h).The average rate of net ozone generation in the same period in September(17.53ppb/h)was higher than that in September at the sampling site(6.90ppb/h).The difference in net formation rate was mainly due to the impact of fixed-source emissions from surrounding companies in the sampling site.The sampling site has the highest proportion of oxygenated volatile organic compounds,and a petrochemical companysampling site has the highest proportion of alkanes.The results of the RIR sensitivity experiment showed that the O3 formation in the three sampling periods was in the VOCs control area.In May 2019,the control of isoprene and aromatic hydrocarbon VOCs can greatly reduce the O3 formation.In September,it was necessary to mainly control the emission of the aromatic hydrocarbons.The sensitivity of oxygen organics in November 2020 actually indicated that the O3 fomation in winter was mainly controlled by the aromatic hydrocarbons.For the VOCs monomer,reducing the concentration of meta-xylene during the three sampling periods had the greatest impact on the O3 formation.(4)By calculating the contribution of VOCs to SOA,it can be seen that the∑SOA_p in May2019 was the highest,which was 324.91μg/m~3,and the∑SOA_p in September and November2020 were 128.91μg/m~3 and 151.75μg/m~3,respectively.The SOAp contribution of aromatic hydrocarbons in the three sampling periods was above 92%,and the species with the highest contribution was toluene.The fifth ranked SOAp in the three sampling periods were all aromatic hydrocarbons,namely toluene,para-xylene,ethylbenzene,o-xylene and benzene;During the PM2.5 pollution period,with the aggravation of the pollution level,the SOAp value of p-m-xylene gradually increased,and the SOAp of both o-xylene and ethylbenzene showed a characteristic of gentle increase.Therefore,in order to control the generation of SOA,the fixed source emissions of para-m-xylene,o-xylene and ethylbenzene should be controled.In May2019,the change trends of SOC and SOA were consistent with the change trends of OC4 and aromatic SOAp.Road dust in the sandy season in May has a significant impact on the contribution of SOA generation.Therefore,the transportation of large diesel trucks and muck trucks at night should be strictly controlled.(5)The VOCs data of the navigation found that the emission of VOCs around the sampling point may be affected by the solvent and oil paint used in the surface painting of a machining enterprise factory area and the exhaust emissions of motor vehicles at the intersection of the main road around the point.The concentrations of xylene and ethylbenzene near the high-value points were higher,and the concentrations of both in the plant area were significantly higher than those in the surrounding areas,and the concentration of alkanes(such as nonane,etc.)at road intersections had increased.Combined with the optimal control species,it can be seen that the dominant species of VOCs that contributes o the O3 formation and fine particulate matter PM2.5 was aromatic hydrocarbons.Therefore,it is necessary to strengthen he VOCS emission control with the import and export purification efficiency and minimize the unorganized emission of VOCsin the production process of a machining enterprise.Also,it should strength the traffic suspervision,especially the heavy diesel trucks and strengthen the cleaning of surrounding roads to reduce secondary dust. |
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