Study On Prediction Of Near-surface Ozone And Pollution Prevention And Control Strategy In Main Urban Area Of Lanzhou

In recent years,the problem of ozone pollution in China has become increasingly serious.As an important heavy industry base in the west of China,Lanzhou is dominated by petroleum and chemical industries.With the acceleration of industrialization and urbanization,the problem of ozone pollution has become increasingly prominent and has become the primary pollutant affecting the ambient air quality.Therefore,early warning of ozone pollution in the future and taking corresponding precursor emergency measures to prevent and control the occurrence of heavily polluted ozone weather are of great significance for promoting the prevention and control of ozone pollution in Lanzhou City.Based on the data of ozone,NO_x,VOCs and meteorological automatic monitoring from March to September,2020,the pollution characteristics of ozone and its precursors,VOCs and NO_x,and the correlation between meteorological factors and ozone pollution in Lanzhou city were analyzed.By inputting the monitoring data and pollution characteristics into OZIPR air quality model,the sensitivity of ozone generation in the main urban area of Lanzhou in three seasons was obtained,and the sources of ozone precursors in the main urban area of Lanzhou were analyzed based on literature research and orthogonal matrix decomposition model（PMF）,and the prevention and control strategies of ozone pollution were put forward in combination with the above analysis.Finally,the results of pollution characteristic analysis are taken as the characteristic factors of long-short-term memory neural network（LSTM）,and the LSTM model is used to predict the ozone concentration in the future,to warn the ozone pollution.At the same time,the LSTM model is used to evaluate the prevention and control effect of ozone precursor emission reduction on ozone pollution again.Finally,the early warning and prevention and control strategy of ozone pollution in the main urban area of Lanzhou City was completed.The main research results are as follows:（1）Characteristics of near-surface ozone pollution in the main urban area of Lanzhou:From March to September,2020,the eight-hour average ozone concentration(O_3-8h)in the main urban area of Lanzhou showed a trend of first increasing and then decreasing,and the peak value appeared in July.O3-8h exceeded the standard for 30 days.NO_x pollution in the main urban area of Lanzhou is mainly NO₂.The dominant species of VOCs in the main urban area of Lanzhou are OVOCs such as C₂～C₅ alkanes,formaldehyde and acetaldehyde,and halogenated hydrocarbons such as dichloromethane and chloroform.Meteorological factors related to ozone pollution include temperature,relative humidity,wind speed and the height of atmospheric mixed layer.Ozone concentration is positively correlated with temperature and wind speed,and negatively correlated with relative humidity.Before16 o’clock,ozone concentration is positively correlated with the height of atmospheric mixed layer,but after 16 o’clock,there is no obvious correlation.（2）Sensitivity of ozone generation in Lanzhou urban area:Ozone generation in Lanzhou urban area is mainly controlled by NO_x in spring and summer,and by VOCs and NO_x in autumn.At 8:00～12:00 every day,the ozone concentration is low,and at13:00～18:00,there will be a time when the ozone concentration is the highest in a day,and high-concentration ozone pollution also occurs during this time.During this time,the ozone generation in three seasons is controlled by NO_x.Therefore,to control ozone pollution in the main urban area of Lanzhou,VOCs should be controlled based on NO_x control,especially VOCs which contribute greatly to ozone generation.（3）Sources of ozone precursors in the main urban area of Lanzhou City:The main sources of NO_x are industrial sources and traffic sources,while the power sources and civil sources are secondary sources.VOCs that contribute greatly to ozone formation potential（OFP）are OVOCs and olefins.VOCs,which contribute a lot to OFP,have different sources in each season.There are four sources in spring,namely industrial source,biomass combustion source,motor vehicle emission source and natural source.There are five sources in summer,namely industrial source,solvent source,natural source,biomass combustion source and motor vehicle emission source;There are four sources in autumn,namely industrial source,solvent use source,motor vehicle emission source and natural source.（4）Prediction and early warning of near-surface ozone in Lanzhou city:LSTM model shows satisfactory prediction performance in the near-surface ozone prediction in Lanzhou city.It is predicted that the air quality standard（160μg/m³）will be exceeded in the next 1 to 6 hours.The model performs well in predicting the maximum concentration of O_3-8h in the next 1 to 3 days.LSTM can timely warn the ozone pollution in the main urban area of Lanzhou in the future.（5）Evaluation of the prevention and control strategy of ozone pollution near the ground in the main urban area of Lanzhou:According to the sensitivity analysis and precursor source analysis,to control the ozone pollution in the main urban area of Lanzhou in the future,it is mainly necessary to reduce the industrial source emissions and traffic source emissions by reducing industrial production,promoting new energy vehicles and limiting traffic,so as to reduce the NO_x concentration.Based on controlling NO_x,the concentration of VOCs is reduced by controlling industrial sources,solvent sources,and motor vehicle emission sources.By predicting the ozone pollution event from 18:00 to 20:00 on August 26th,2020,15 control scenarios were set.When NO_x control is cut by 30%,the ozone pollution control effect is the best,followed by NO_x control cut by 50%and VOCs control cut by 30%.The research results are consistent with the prevention and control strategies proposed based on OZIPR and PMF models.Controlling VOCs based on controlling NO_x can effectively prevent and control future ozone pollution.Through the research on near-surface ozone prediction and pollution control strategies in the main urban area of Lanzhou,this study has drawn the following conclusions:It not only enables early warning of ozone pollution in the main urban area of Lanzhou but also provides guidance for formulating corresponding prevention and control measures,thereby effectively reducing the occurrence and impact of ozone pollution.