Study On The Influence Of Different Chemical Mechanisms On The Simulation Of Near-surface Ozone And Precursors In Shanghai And Surrounding Area

Air quality models are frequently employed in ozone pollution studies,but there are still no established standards for choosing chemical mechanisms,particularly in China.In this study,we first analyzed the meteorological elements and pollutants in Shanghai in the summer of 2017.Subsequently,we applied three different chemical mechanisms（RADM2,SAPRC99,CBMZ）in the air quality model WRF-Chem to simulate the temporal and spatial distribution of ozone and its precursors in Shanghai and its surrounding cities in July 2017.Observational data from surface monitoring stations were also adopted for the comparison of the model simulations.By comparing the model predictions with the observational data,we found that,and found that:（1）The relationship between the concentration of OH simulated by the three chemical mechanisms is RADM2>CBMZ>SAPRC99.Because OH is mainly produced by the photolysis of ozone to O（¹D）and the reaction of O（¹D）with HO₂.The rate of OH production is determined by the ozone concentration,and the relationship between the concentration of ozone is RADM2>CBMZ>SAPRC99.Moreover,compared to the other two mechanisms,SAPRC99predicted a larger concentration of HO₂ in Shanghai.（2）The NO₂ concentration simulated by RADM2 fluctuates greatly with time.RADM2and CBMZ provide greater NO/NO₂ ratio than SAPRC99.In addition,RADM2 predicted the highest HNO₃ among the three mechanisms because the relationship of NO₂ is RADM2>SAPRC99>CBMZ.The higher NO₂ concentration means that NO₂ and OH will react more quickly,producing a larger concentration of HNO₃.（3）By comparing the simulated results with the observed results,we found that the simulated ozone by these mechanisms are consistent with the observed data.And the ozone level predicted by RADM2（R=0.86）is closer to the observed value than that predicted by the other two mechanisms（The R of both SAPRC99 and CBMZ are 0.85）.In addition,simulations using different mechanisms all indicate that Shanghai is VOCs-controlled.（4）These three mechanisms of RADM2,SAPRC99 and CBMZ simulated the trend of ozone and NO₂ change over time in representative cities of the Yangtze River Delta well.From the average error,RADM2 and CBMZ mechanisms overestimate the ozone concentration,while SAPRC99 underestimates the ozone concentration.