Investigation On Scenario Analysis Of Air Quality Improvement Based On WRF-CMAQ Model In Wuhan Urban Area

With rapid urbanization and industrialization,air pollution problem has become more and more serious.The government attaches great importance to the problem and proposes to formulate a series of laws and regulations to reduce the emission of air pollutants,so as to improve air quality.For example,the Wuhan Government published the 13^th five-year plan for environmental protection of Wuhan in 2017,which required a reduction of pollutant emissions to ensure that the annual average concentration of fine particles(PM_2.5)get decreased by 30%in 2020.In 2017,the average annual concentration of PM_2.5 in Wuhan was 53μg/m³,and it is dropped to 45μg/m³ in 2019 with decreased ratio by 15.1%.In October 2019,the 7^thWorld Military Games（WMG）was hold in Wuhan,during which some emission control schemes were carried out to improve air quality in Wuhan.Therefore,it is important to study the air quality improvement based on the emission control schemes from the public policy and major activities,which can provided some principles to design emission reduction schemes.First,the WRF-CMAQ（Weather Research Forecast-Community Multi-scale Air Quality）models are validated,with the observed data from Wuhan meteorological station and air pollution state control quality monitoring station.The results show that the WRF model could well represent the variation trend of temperature,relative humidity and wind velocity in Wuhan,with the correlation coefficients between the simulated and the observed values being0.80,0.78 and 0.54,respectively.The CMAQ model could also well represent the variation trend of PM_2.5,PM₁₀,O₃,NO₂,and CO concentrations in Wuhan,with the correlation coefficients between the simulated and the observed values being 0.68,0.48,0.45,0.23 and0.42,respectively.Second,with the emission reduction schemes from the 13^th five-year plan for environmental protection of Wuhan,this work takes 2017 as the reference year and carries out four scenario simulations to evaluate the changes of air quality in Wuhan.When the two schemes,i.e.,SO₂,NO_x,particles,VOCs being reduced by about 50%、25%、30%、35%and60%、60%、50%、60%,are implemented,the average annual concentrations of PM_2.5in Wuhan decreased by 11.61%,19.31%,while them of O₃in Wuhan increase by 6.15%,19.75%.The reason why O₃gets increased might be that most area in Wuhan are in the VOCs control area,but the ratio of VOCs to NOx is not decreased properly.By BFM（Brute Force Method）,the contributions ratios of the local emission and exogenous input to the concentration of PM_2.5 in Wuhan are 34.35%and 65.65%in 2017.Therefore,to realize the aim of the 13^th five year plan and reduce annual average concentration of PM_2.5 by about 30%,emission reduction in larger areas need to be taken into consideration.For instance,the Wuhan 1+8 city cluster and other cities on the pollutant transmission path are adopt the joint prevention and control policy of pollutant collaborative emission reduction.Third,this paper analyzes the sensitivity of the air quality to the five kinds of local pollutant emission sources in Wuhan.It is concluded that the industry source contributes by about 15.37%to PM_2.5 concentration,followed by residential source,traffic source,agricultural source and power source,with the contribution proportion being 8.13%,5.57%,4.23%,0.90%,respectively.In addition,when the traffic,power and industrial sources are totally reduced,the annual concentration of O₃ in Wuhan gets increased.When the residential source is totally reduced,O₃ concentration in Wuhan decreases by 3.35%.In contrast,the contribution of the agricultural sources is negligible to the change of O₃ concentration in Wuhan.Thus,to the decrease of PM_2.5 and O₃ concentrations,the reduction of residential source and agricultural source can lead to the air quality improvement.The reduction of residential source and agricultural source should be considered in the further formulation of pollutant control strategies.Finally,the air quality in Wuhan 1+8 city cluster with emission control strategies during WMG is simulated.This paper analyzes the historical air quality of the past six years in the same period,and finds the primary pollutants,i.e.,NO₂,O₃,PM_2.5 during this period.When the emission control schemes are carried out in the Wuhan 1+8 city cluster and only in Wuhan during WMG,the average concentration of PM_2.5 of in Wuhan decreases by 11.73%and 7.14%,respectively.Thus,it is concluded that the contribution of emission reduction in city cluster to pollutant concentration reduction in Wuhan is greater than that implemented only in Wuhan.