Analysis And Numerical Simulation Of Heavy Air Pollution Process In Southern Sichuan Urban Agglomeration

The paper,aimed at the air pollution prevention and control work in southern Sichuan,carries out a detailed analysis of the pollution change features and meteorological causes of an interannual severe air pollution process in the southern Sichuan urban agglomeration occurring from December 26,2016 to January 11,2017,through the application of the observation data and meteorological data of air pollutant concentration of southern Sichuan urban agglomerations(Yibin,Zigong,Luzhou,Neijiang,Leshan),with such methods as mathematical statistics and diagnostic analysis of polluted weather and the like.Moreover on this basis,with two physical parameterization projects,simulate the two pollution processes occurring in the southern Sichuan urban agglomeration from December 15,2016 to January 11,2017 by using the coupling modes of WRF-Chem and WRF-CUACE.Find out the deficiencies of the mode and propose suggestions for improvement through the comparison of observation and simulation results.The main conclusions reached are as follows:(1)Direct at this pollution process,the south trough plays a key role in the formation and maintenance of the static stability of atmosphere(isothermal or inversion layer).The south trough intensifies and leads the southwest dry and warm air in front of trough to move north,causing the local lower atmosphere to warm,forming a low-altitude isothermal or inversion layer,and imposing restrictions on the diffusion of local atmospheric pollutants,which is the main weather system that facilitates the formation of this heavy pollution process.Heavy pollution is formed under this condition coupled with high humidity and low-altitude wind direction convergence;and then the south trough weakens,so does static stability of atmosphere.The lower-seam wind direction convergence disappears;the atmospheric diffusibility is enhanced,and the pollution concentration is reduced;at last,the local pollutant concentration drops rapidly by the wet removal effect of the superimposed precipitation,and the pollution process ends.(2)It is considered that,by comparing the difference between the simulation results and the observed values,the 4 groups of experiments generally have good simulation results for 2 m temperature,overestimating the wind speed of 10 m and the peak concentration of PM_2.5.The simulation results of aerosol constituents show that the ratio of NO₃^-is higher,the ratio of NH₄⁺is obviously lower,the ratio of BC is higher,the ratio of OC is slightly lower,and SO₄^2-ratio is highly sensitive to changes in physical schemes,among which,physical scheme 2 is relatively high,and physical scheme 1 is low.Furthermore,the concentration of SO₄^2-increases remarkably in the early stage of pollution aggravation affected by heterogeneous reaction,and it is more obvious in the CUACE simulation results.It is concluded that the mode should be further improved in the aspects of meteorological model at static conditions,peak concentration of PM_2.5,and the mutual transformation mechanism between nitrate,sulfate and their precursors.(3)Taken the simulation results of meteorology,PM_2.5concentration and aerosol constituents together,it holds that the simulation result of CUACE2 is the best,which is also the best for sulfate among the 4 groups of experiments on the premise of ensuring a good simulation result of PM_2.5concentration.The similar result,although,is seen for Chem2 in the simulation of sulfate constituents,it is found that CUACE2showed the lower PM_2.5concentration and SO₂concentration than Chem2 after the comparison.In general,the simulation effect of CUACE2 is regarded as the best in the 4 groups of experiments.This paper has found the key role of the south trough in the pollution process through the analysis of the severe air pollution process in southern Sichuan.Then the pollution process of southern Sichuan is simulated by using numerical model,and the physical and chemical modes with better effects in southern Sichuan are analyzed,and the deficiencies of the related numerical models are found based on the difference between the simulation and observation,which is of important scientific significance to further analyze and deepen the understanding of the formation and maintenance mechanism of the heavy pollution process in the future,as well as to know the change mechanism of aerosol constituents in the process of pollution,and to improve the performance of the mode.