Simulation Study Of Ozone Formation And Cause Analysis In Typical Plateau And Mountainous Cities

Near-surface ozone showed a fluctuating-upward trend in China’s urban and regional areas in recent years.Ozone has become a key factor in improving air quality and a significant adverse health effect.Ozone formation in different regions varies substantially due to complicated emission sources,topographical and meteorological factors,and regional transport.Compared to cities in the Jing-Jin-Ji Region,the Yangtze River Delta,and the Pearl River Delta,the formation of near-surface ozone in the plateau and mountainous municipalities in Southwestern China are limitedly investigated.Plateau and mountainous cities are more influenced by intense solar radiation,complex terrain,and various emission sources.The related studies are important for better understanding the atmospheric chemistry processes and improving air quality,which is a national requirement.This study focuses on the formation of near-surface ozone in representative mountainous(Chongqing)and plateau(Lhasa)cities.We figured out the distribution characteristics and the transmission mechanism of near-surface ozone.We developed a localized parameterization method for ozone simulations.We discussed the formation mechanism of near-surface ozone and the influence of key anthropogenic sources.The results can give a better direction to these two cities in emission reduction policies and provide scientific support for similar studies.This study obtains the following main results:(1)We obtained the spatial-temporal distribution of near-surface O3 using ground-based and vertical observations and model simulation and discussed the pollution transmission mechanism and the effect of meteorological factors.The distribution of near-surface O3 concentration strongly correlates with the planet boundary layer height(BLH).The BLH in summer ranges from 1 to 1.5 km,and the high value of O3 concentration is concentrated within 0.8 km in Chongqing.In comparison,in Lhasa,the BLH ranges from 1 to 1.2 km in summer,and the high value of O3 concentration is concentrated within 0.4 km.The highest ozone concentration occurred in May when the temperature and solar radiation were highest in Lhasa.The spatial distribution of O3 during the high concentration period presents a local generation-accumulation-titration diurnal trend.It has emphasized the conclusion that local photochemical reactions mainly dominate the near-surface O3 pollution in high-altitude cities like Lhasa.We also discovered that the local NOx titration effect is less,which is why the higher concentration background value is at night,with the simulation of ozone budget transmission and trajectory analysis.In comparison,the high value of O3 in Chongqing appeared from July to August,and high temperature is the main driving factor.Precursors of O3,including NO2 and HCHO,are mainly distributed within 0.4 km,indicating that the "source" and reaction of O3 are concentrated on the near surface.Sensitivity analysis in the vertical dimension shows that O3 formation is in a VOC-limited regime within the height of 0.4 km and in a transition regime above 0.4 km.It is necessary to comprehensively consider the control of NOx emissions in the upwind overhead direction of mountainous areas.(2)We developed a new parameterization method for ozone simulations in plateau and mountainous cities.We improved the accuracy of the simulation by evaluating the BLH,lifting time and photolysis coefficient(both in measurement and simulation)based on the OBM(Observation Based Model).The alternation of BLH is one of the constraining factors for vertical mixing and dilution.The photolysis coefficient participates in the calculation of the chemical reactions and is used as the key physical parameter of the verification model.When the BLH was set to 1 to 1.2 km in summer and raised from 8:00 to 18:00,the simulation effect of O3 concentration was substantially improved.The simulated value of the photolysis coefficient overestimates the measured value by about 42%over Chongqing in summer.The optimal effect of O3 simulation is achieved using the measured photolysis coefficient constraint in summer when the BLH is 1 to 1.5 km and the lifting time is between 8:00 and 18:00.The improved model can reasonably simulate the formation mechanism and cause of O3 in these two plateau and mountainous cities.The technical requirements of atmospheric physical parameters as revision input module have been applied in OBM model development.(3)We quantified the reduction effect of key pollutants on O3 response by coupling source apportionment of the receptor model as well as the OBM model.We obtained the reduction strategy of VOCs from anthropogenic sources and the practical results of sensitive analysis of O3 formation both in representative cities like Chongqing and Lhasa.Like most suburban areas,Lhasa was in the communal transition region of VOCs and NOx.The RIR values suggest a sensitive order of anthropogenic VOCs,NOx,biogenic VOCs,and CO.Significant emissions from motor vehicle exhaust,gasoline volatilization,solvent paint,and incense burning among the VOCs precursors reflect strong anthropogenic influence.We found that the priority of potential ozone reduction was combustion>traffic>solvent coatings≈industrial emissions.Like most urban areas,O3 formation in urban Chongqing is in a VOC-limited region.In addition to anthropogenic alkanes and alkenes,VOCs from natural sources were also strong in summer.Consequently,enhanced reductions in motor vehicle emissions,industry and solvent use are effective controls.OFP reduction efficiency was ranked as vehicle exhaust>solvent use≈Industrial emission≈gasoline volatilization.We recommended that the optimal reduction ratio of VOCs and NOx emissions should be 3:1 in both cities,and the control of NOx would be in priority.