Study On The Interaction Between Atmospheric Particulate Matter And Ozone In Dongying

At present,strengthening the collaborative control of fine particulate matter(PM_2.5)and ozone（O₃）has become the focus of air pollution prevention and control in China.Due to the complex interaction between atmospheric particulate matter and O₃,it is of great significance to understand the formation mechanism of PM_2.5 and O₃ combined pollution and to clarify the collaborative prevention and control mechanism of PM_2.5and O₃.This research comprehensively utilizes field observation,laboratory analysis,OBM（Observation Based Model）simulation and other methods to clarify the pollution characteristics of PM_2.5 and O₃ in Dongying from 2017 to 2022.The interaction between atmospheric particulate matter and O₃ in typical pollution processes was analyzed from two aspects:the influence of aerosol optical properties on O₃ generation and the influence of atmospheric oxidation capacity on nitrate（NO₃^-）generation in PM_2.5.The main conclusions are as follows:From 2017 to 2022,the annual assessed value of PM_2.5 concentration in Dongying showed a downward trend from 55μg/m³ to 33μg/m³,while the annual assessed value of O₃ concentration showed a fluctuating upward trend from 176μg/m³ to 185μg/m³.In terms of the correlation between PM_2.5 and O₃ concentration,it showed a negative correlation in winter（correlation coefficient range is-0.24～-0.11）,and a significant positive correlation in summer（correlation coefficient range is 0.56～0.67）,while a weak positive correlation in spring and autumn（correlation coefficient range is0.06～0.24）.The correlation coefficient between PM_2.5 and O₃ concentration shows a fluctuating and rising change characteristic,indicating that the correlation between PM_2.5 and O₃ is gradually increasing in recent years.When the correlation between PM_2.5 and the daily value of O₃ is strong,the air temperature is 15～20℃and the atmospheric oxidation capacity（characterized by the concentration of atmospheric odd oxygen（O_X=NO₂+O₃））is high（O_X concentration is greater than 125μg/m³）.From the distribution of primary pollutants,there are usually 3 to 4 primary pollutants from January to March and from October to December,and it is easy to occur atmospheric composite pollution.The aerosol scattering coefficient of Dongying showed obvious seasonal variation,reaching the highest level in autumn(400.62 Mm^-1)and the lowest level in summer(161.06 Mm^-1).In the four typical pollution processes,the contribution of ammonium nitrate（NH₄NO₃）to the extinction coefficient of aerosol in PM_2.5 in autumn,winter,spring and summer is the largest,reaching 71%,43%,55%and 46%respectively.The extinction effect of aerosols in autumn,winter,spring and summer can lead to the decrease of NO₂ photolysis rate(J（NO₂）by 11%,26%,18%and 39%,respectively,and further lead to the decrease of O₃ concentration by 9%,21%,18%and 29%,respectively,indicating that the radiative forcing of aerosols can significantly inhibit O₃ generation.O_X concentration in Dongying varied from high to low is summer,spring,autumn,winter from 2017 to 2022.In the four typical pollution processes in spring,summer,autumn and winter,atmospheric oxidation capacity can significantly affect NO₃^-generation in PM_2.5.In summer,atmospheric oxidation capacity has the most significant effect on HNO₃ mass transfer process,which can increase the reaction rate by 101%.In winter,atmospheric oxidation capacity has the most significant effect on N₂O₅heterogeneous hydrolysis process,which can increase the reaction rate by 127%.The NO₃^-generation rate in PM_2.5 ranked from high to low is autumn,winter,spring,summer.From the proportion of different reaction pathways,the proportion of N₂O₅heterogeneous reaction rate ranked as autumn,summer,winter,spring,which were 39%,38%,27%and 25%,respectively.The contribution of different VOCs components to O₃ generation is olefin,OVOCs,alkanes,aromatic hydrocarbons,which indicated that the potential contribution of VOCs such as olefin,OVOCs and alkanes to O₃ generation is high,which is an important factor affecting the atmospheric oxidation capacity of Dongying.In general,there is a complex chemical coupling mechanism between PM_2.5 and O₃ in Dongying.The higher the temperature and the stronger the atmospheric oxidation capacity,the stronger the positive correlation between the two.When the temperature is lower and the atmospheric oxidation capacity is weaker,the positive correlation between the two is weaker.Due to the important influence of aerosol optical characteristics and atmospheric oxidation capacity in different seasons on the generation of PM_2.5 and O₃,Dongying needs to focus on the prevention and control of active species in VOCs to reduce the atmospheric oxidation capacity,so as to achieve the purpose of collaborative prevention and control of PM_2.5 and O₃.