Variation Characteristics Of Surface Ozone Concentration And Numerical Simulation Of Its Formation Process In Guanzhong Region

In recent years,following PM_2.5,O₃ has become the secondary significant pollutant affecting air quality in Guanzhong Region.This paper analyzes the concentration status and the constituent feature of O₃ and its precursor in Guanzhong Region,based on the 6 typical pollutants data from 33 national monitoring sites in 2017,and the VOCs concentration measured in autumn.In addition,according to the simplification mechanism of photochemical reaction proposed by the famous atmospheric chemist Seinfeld,this study established a reaction kinetic equation that involves participated substances.By giving the initial condition and control conditions of differential equation,the dynamic equations were solved by the MATLAB numerical solution tool.The concentration of the reactant and product in8:00-18:00 photochemical reaction varying with time was carried out as well.Conducting a Quantitative analysis on the effects of the transformation of the concentration of NOx and VOCs on the concentration of photochemical oxidant,such as O₃、PANs and RCHO.Furthermore,the effect of different components of VOCs and the temperature on the formation of photochemical oxidant were analyzed.Major conclusions are as follows:（1）The average concentration of O₃ in 2017 in Guanzhong Region was 54.30±48.90μg/m³.The concentrations of O₃ concentration was highest in summer（90.13±54.13μg/m³）,followed by spring and autumn（61.41±41.35μg/m³,33.25±30.88μg/m³）,and lowest in the winter（31.86±23.75μg/m³）.Annual 90^th percentile O₃-8h concentration in Baoji,Xianyang,Xi’an,Tongchuan,and Weinian cities in GuanZhong Region were 153、196、180、164 and 179μg/m³,respectively.The number of polluted day were 27、73、60、45 and 62.The only city that reached the air quality standard of O₃ is Baoji.The most polluted city is Xianyang.（2）The analysis on the concentration and the components of VOCs in the area showed that the average volume concentration of VOCs was 66.45 ppbv in autumn;the concentration of top 3 components of VOCs were alkanes,aromatics and OVOCs,distributed as 31.94%、18.84%and 15.27%,respectively.The concentration of top 3 components of ozone formation potential（OFP）were alkenes,aromatics and OVOCs.Their contribution to OFP were 42.97%、28.13%and 14.35%.（3）The numerical simulation results of photochemistry reaction showed that under the circumstance of constant VOCs concentration,with the initial concentration of NO or NO₂was increased,the maximum level of O₃ and PANs would increase.Meanwhile,the peak concentration time of O₃ and PANs would delay,the duration of high concentration of PANs decreased.In addition,when the concentration of NOx keeps constant,the concentration of PANs and O₃ would benefit from the higher concentration of NO₂.（4）The effects of VOCs on the formation of photochemical oxidants showed that as the initial concentration of RH、HCHO and RCHO were increased,the peak concentration of O₃and PANs enlarged as well and the time of O₃ and PANs reached their peak concentration were advanced.Moreover,RH had a significance impact on the concentration of O₃ as well as RH and RCHO had a significance impact on the concentration of PANs.（5）The analysis on numerical simulation showed that if the concentration of NOx maintains constant in the area,RH,RCHO and HCHO were increased by 50%respectively which would lead to magnify O₃max and PANs max.On the contrary,if the concentration of RH、RCHO and HCHO were decreased by 50%respectively,the decreasing amplitude of O₃max and PANs max were greater.Alkenes and aromatics were the components that generated the greatest contribution to the product of O₃ and PANs.Therefore,regulating the emission of alkenes and aromatics can effectively reduce the concentration of O₃ and PANs in the Guanzhong Region.