Influence Of The Background Nitrogen Oxides On The Tropospheric Ozone Depletion In Arctic During Springtime

Ozone depletion events?ODEs?in the springtime of the Arctic have been frequently observed since the early 1980s,and the correlation between the ozone mixing ratio during the ODEs and the nitrogen oxides?NO_x?concentration is still unclear.In the present study,a zero-dimensional box model KINAL?KInetic a NALysis of reaction mechanics?was used to simulate ODEs under a typical Arctic atmosphere background.The chemical reaction mechanism included 141 reactions and 49 species.By changing the initial concentration of nitrogen oxides?NO_x?in the model,the effect of the initial NO_xconcentration on the ozone mixing ratio and halogen cycle was studied.Then the relative concentration sensitivity analysis was used to explore the role of NO_x in ODEs and to analyze the influence of various substances on the NO_x concentration.The main findings are as follows:?1?During ODEs,the concentrations of NO and NO₂ decreased sharply in the first two days,and the concentrations of HNO₃,HONO and PAN increased steadily during the simulated 10 days.The concentration of HNO₄ reached a peak at the beginning of the reaction,then dropped to a value close to zero within two days,and remained low until the end of the ozone depletion simulation.?2?In the ozone depletion process of the standard case?15 ppt initial NO_x concentration?,ozone is most affected by the initial concentration of CH₃CHO,and the increase of the initial concentration of CH₃CHO will retard ODEs.The increase of the initial HCHO and CO concentrations will accelerate the rate of ozone depletion.The second most important effect on ozone is Br₂,which is due to the key role of Br₂ in the bromine explosion mechanism,and the ozone concentration sensitivity corresponding to HBr is negligible.?3?The effect of the initial NO_x concentration on ODEs has two sides.There is a critical value of initial NO_x concentration,which makes the ozone depletion rate independent of the initial NO_x.In this study,the critical value is about 55 ppt.When the initial concentration of NO_x is below the critical value?<55 ppt?,the ozone concentration is negatively correlated with the initial NO_x value,and NO_x promotes ozone depletion.On the contrary,when the initial concentration of NO_x is above this value?>55 ppt?,the ozone concentration is positively correlated with the initial NO_x value and NO_x would retarded ODEs.