The Characteristics Of Ozone Pollution And Its Nonlinear Response To Precursor Emissions In Huhhot-Baotou-Erdos Region

Facing an increasingly serious issue of ground-level ozone pollution in China,a pollution control system for ozone is urgent to be developed.As the scientific basis of the system,three main topics,namely the emission inventory of ozone's precursors?NO_X and VOCs?,the mechanism of ozone formation,and the nonlinear response of ozone concentration to its precursor emission,need to be studied.Taking Hohhot-Baotou-Erdos city cluster as an example of western cities,the effects of precursors'emission on ozone formation in this area was analyzed,to support future policy-making for ground-level ozone pollution control in China.In this study,a high-resolution emission inventory?EI?of open biomass burning,together with a high-resolution emission inventory of major sources,such as power plant,industrial sector,and transportation,was developed.The open biomass burning EI was estimated by an updated method,which used multiple satellite data,and localized emission factors and combustion factors.This EI could significantly improve the ground-level simulation results,especially during the period of massive open burning.The pollution characteristics of ozone and its precursors were also analyzed.The results showed that the ozone concentration in urban and industrial area,as well as background continued longer at high level than eastern cities.Although the concentration of NO_X and VOCs was generally low,the ozone concentration in urban and industrial area was comparable with those cities in eastern China.High chemical reactivity speicies of VOCs were found to classify to alkenes and aromatics.Through simulation by CMAQ model,this paper analyzed the process of free radicals generation,chain reactions and terminate reactions in different regions.The results showed that OH radicals in urban and industrial area mainly generated from the photolysis of ozone and HONO,but the OH radicals in background area mostly generated from the photolysis of ozone,and removed by reaction with CH₄.Both RO₂ and HO₂ radicals generated from the reaction between OH radicals and VOCs,which were dominated by alkenes and aldehydes.The HO₂radical in urban was removed by transforming to OH,but the HO₂ radical in background area was removed by the termination reaction of HO₂.The HO₂ radical in industrial area can be removed in both way above.The isoconcentration curves of ozone in four functional areas,namely urban,industrial area,suburban and rural area,were established by simulating under multiple emission abatement scenarios.The scenario analysis results showed that the sensitivity characteristics of ozone may be affected by varied meteorological conditions.The same NO_X control zone was found in rural area,but varied control zone were found in both polluted days and clean days.In general,ozone sensitivity characteristics presented VOCs control zone in urban,NO_X control area in rural,transition region in industrial area and suburban.Based on the comparison of various reduction scenarios of emission,the most optimal stratege of VOCs and NO_X emission abatement were VOCs/NO_X=3:1 in urban.The sensitivity experiment showed that alkenes emission should be prior to reduce to control the ozone concentration in urban and suburban.