Study On The Influence Factors Of Ozone Pollution And The Numerical Simulation Of Typical Cases In Lanzhou

In recent years,many cities at home and abroad have experienced ozone（O₃）exceeding the standard,O₃ pollution has gradually become prominent and gradually become another important atmospheric pollutant that affects human health and the ecological environment after PM_2.5.The influcing factors of O₃ pollution are very complicated and gradually become the focus of research.Lanzhou is the earliest industrial area in China.It was once the focus of attention at home and abroad due to pollution problems.Lanzhou was also the first city in China where photochemical smog was observed.In recent years,the concentration of O₃ in Lanzhou area has been rising and exceeding the standard,which has threatened people’s health and ecological environment.Therefore,studying O₃ pollution in Lanzhou has important practical significance.Results from our study can provide some scientific reference for the prevention and control and prevention of O₃pollution in Lanzhou.In this paper,data of meteorological elements and atmospheric pollution in Lanzhou from January 1,2013 to July 31,2017 were used to analyze the spatial-temporal distribution characteristics of O₃ concentration in Lanzhou and the influence of meteorological elements on the changes of O₃ concentration.On this basis,the generalized phase based on the control of long-term trends,seasonal effects,and weekend effects,a generalized additive model（GAM）was performed to study the complex non-linear relationship between O₃ concentration and its influencing factors in Lanzhou,and we also established a multi-factor model with interactive terms.The effects of different factors and their interactions on the changes of O₃ concentration were thoroughly analyzed.Furthormore,in the analysis of typical case,the weather field and pollutant concentrations during an O₃ pollution process in summer were simulated using the WRF-Chem model,and the results were compared with the observed values.Combined with the point-by-point analysis of the O₃ pollution process,the causes of O₃ pollution in Lanzhou were further explored.The main findings are as follows:（1）From 2013 to 2017,the concentration of O₃ and NO₂ in Lanzhou increased year by year.The concentration of particulate matter decreased slightly,while the concentration of SO₂decreased more obviously.The air quality in Lanzhou has improved.The number of good days is the most,and the average compliance rate is 64%.The increasing O₃ concentration in recent years has posed a potential threat to air quality in Lanzhou.（2）The daily variation of O₃ concentration in Lanzhou presents a typical“single-peak type”.The O₃ concentration is highest at 14:00-16:00 and lowest at 06:00-08:00.The diurnal variation of the concentration of O₃ and its precursor NO₂ showed the opposite trend,and there was a significant negative correlation between the two pollutants.The O₃ concentration has obvious seasonal changes and presents an inverted"U"shape.The O₃ concentration is highest in summer（June-August）,decreases rapidly after September,and the lowest O₃ concentration in winter（December）.Particulate matter concentration is higher in spring and winter,while O₃ is higher in summer,presenting a tendency of"cross-contamination".Particulate matter and O₃ interact with each other,and O₃ gradually becomes the most important pollutant in Lanzhou after particulate matter.The near-surface O₃ concentration in Lanzhou is closely related to meteorological elements.Among them,the hours of sunshine and daily average temperature are significantly positively related to O₃ concentration.When the relative humidity is less than 40%,the number of days exceeding the standard is the highest;when it is greater than 60%,the number of days exceeding the standard is significantly reduced;in the case of soft wind and no precipitation,the number of days exceeding the standard is the highest and the accompanying O₃ concentration is high.Generally,longer sunshine,high temperatures,low humidity,light wind,and no precipitation are favorable conditions for high concentrations of O_3.（3）The single factor GAM hypothesis test results show that the adjusted coefficient（R²）of the model is 0.594,and the interpretation rate of the variance of O₃ concentration is 62.3%,among which the temperature explains 24.2%of the variance of O₃ concentration（F=350.84）,temperature is the main driver factor of O₃ concentration change.Combining with the partial response diagnostic analysis of O₃ concentration,O₃ concentration in Lanzhou has significant non-linear relationships with T,W,SH,RH,NO₂,and PM_2.5,and it has basically linear relationships with P and CO.T,,RH,NO₂,and PM_2.5.5 have significant effects on O₃concentration.The multi-factor GAM model with interactions has an adjustment judgment coefficient of 0.636,a variance interpretation rate of 68.1%,and a good model fitting degree.The interaction between influencing factors has a higher interpretation rate for the change of O₃concentration in Lanzhou.The interaction term is mainly in the form of“meteorological elements+pollutants”.Among them,the interaction between temperature and wind speed has the most significant effect on the change of O₃ concentration.It further proves that temperature is an important factor affecting the change of O₃ concentration in Lanzhou.Constructing an interactive GAM model can quantitatively and visually analyze the changing characteristics of O₃concentration in Lanzhou and complex non-linear relationships.（4）The simulation results in WRF-Chem mode show that the consistency index（IOA）of O₃is 0.90 and the IOA value of NO₂ is 0.76.The simulation effect is better overall,and it can better reflect the characteristics of pollutant concentration changes with time.The diurnal variation of O₃concentration simulated by the model presents a clear“single peak type”,which is basically consistent with the trend of observed values.However,the effect of pollutant concentration simulation is not as good as that of the meteorological field（2m temperature and relative humidity）,especially the peak value and the time when the pollutants appear.This may be related to the list of emission sources,the selection of parameterization schemes,and model errors.According to the H₂O₂/HNO₃ ratio method,O₃ pollution in Lanzhou belongs to the NO_X control zone.The NO_X control measures can be used to reduce O₃ pollution and provide a scientific basis for the prevention and control of O₃ pollution in Lanzhou.Based on the results of analysis simulation and point-by-point analysis,the O₃ pollution process in Lanzhou was caused by the combination of meteorological factors,local generation,and regional transmission.