| The frequent air quality problems in our country caused by the development of industrial and economic development have aroused humen concern.Ozone pollution was increasingly serious,which was one of the main primary pollutants in China.High concentration of ozone has adverse effects on human health,animals and plants growth,and climate change.The aggregation of factories causes plenty of pollutants with high concentration and complex composition emitted from chemical industrial parks,which influenced the air quality of the park and nearby region,especially ozone pollution.The small-scale ozone pollution research in the park can support the scientific preventation and control of ozone in the park,and meet the prevention and control needs of key regions in our country.Therefore,a typical chemical industrial park in the Yangtz River Delta was selected to excavate the ozone formation rules in the environmental monitoring data,identify the emission characteristics of key VOCs pollution sources and priority control species,calculate the degradation mechanism of the characteristic pollutant and explore its impact on ozone formation,and carry out source tracing and emission reduction scenario analysis.All these work provide scientific and effective guidance for the air quality improvement in the park and surrounding areas.Based on the online monitoring data of atmospheric pollutants and meteorological factors in the chemical industrial park,the variation characteristics of ozone and its influencing factors was discussed for detail.The temporal variation and correlation analysis results showed that ozone was more correlated with NO2,temperature and relative humidity than other factors.In addition,the GBDT(Gradient Boosting Decision Tree)model of machine learning was used to explore the ozone formation rules in the park with complex composition.The whole year was divided by 15℃ for three periods,and the input data settings of GBDT model was constructed by different feature processing methods for training GBDT model.The results showed that ozone formation in the park were most affected by relative humidity,temperature,NO2 and PM2.5.Ozone pollution was more sensitive to meteorological factors than precursors.Ozone concentration increased unevenly with the increase of temperature,while it increased at first and then decreased with the increase of relative humidity.Weather with relative humidity lower than 70%and temperature larger than 25℃ was more prone to heavy ozone pollution.Combine GBDT model prediction method,VOCs/NOx method and ozone dynamic contour method for judging ozone sensitivity,and results showed that ozone was alternately sensitive to VOCs and NOx,and VOCs have greater reduction space than NOx because of its emission characteristics.Therefore,the regulation of NOx can achieve obvious ozone control effect in the short term,while the reduction of VOCs was still the key strategies in the long term.Therefore,process-based VOCs source profiles were built for key industries in the park to identify VOCs emission characteristics further.The VOCs source profiles for twenty-five production units of bulk chemical raw material manufacturing,primary form plastics and resin manufacturing,synthetic rubber manufacturing,plywood manufacturing,crude oil storage and processingindustries were built.It was found that aromatics,halocarbons and alkanes accounted fot the highest,toluene and dichloromethane were the main VOCs species in the park.Combined with VOCs composition characteristics and ozone formation potential analysis,toluene and other aromatics were the priority control species for ozone pollution in the park,and the influence of dichloromethane on ozone pollution was worth further research.Quantum chemical calculation was used for exploring the degradation mechanism of dichloromethane and its effects on ozone formation.The results showed that the H atom extraction path had a significant advantage over the replacement path in the reaction of dichloromethane and NO3 radical.Subsequently,the reaction batween CHCl2 and NO2 brached into 14 reaction pathes and 6 products since it attacked O atom or N atom to form different intermediates The reaction rate constants and branch ratio results showed that the path of CHCl2+NO2→CHClO+ClNO played a decisive role in the whole reaction.ClNO could be converted into Cl atom by photolysis or hydrolysis in the atmosphere,and then Cl atom would affect the generation of free radicals and the chemical reactions of VOCs to change the atmospheric oxidizing capacity and the reaction direction of ozone.The atmosphere reaction mechanism of dichloromethane was an important supplement to the ozone formation mechanism in the park.Finally,combined the localized pollution source emission inventory and species allocation system of the park,the WRF-CMAQ(Weather Research and ForecastCommunity Multiscale Air Quality)model was used to carry out the simulation and source tracing of ozone,which reappeared the whole formation process of atmospheric pollution in the park.Source tracing results showed that non-local sources contributed the most for VOCs,NOx and ozone;in local sources,industrial sources and mobile sources were the largest contributor for ozone pollution in VOCs-sensitive and NOxsensitive periods,accounting for 66.33%and 50.62%respectively.The massive local emission of VOCs and NOx in the park enhanced the oxidization of the atmosphere and lead to high-ozone concentration.In addition,two emission reduction scenarios were set up according to the planning of the park and nearby region,and the average annual declines of scenarios Ⅰ and Ⅱ compared to the baseline scenario were 3.12 μg·m-3 and 4.84 μg·m-3,respectively.Positive reduction of precursors can significantly reduce ozone concentration in all seasons except winter.Based on the source tracking results of muti-pollutnat to promote the coordinated prevention and control strategies in the park,it is meaningful to refine the pollution control strategies of factories,strengthen the treatment of fugitive VOCs emissions,improve the motor vehicle emission monitoring system,and value regional joint prevention and control and so on. |
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