Research On Pollution Assessment Of Sudden Accidents Based On Mesoscale Meteorological Model Dat

In recent years,in addition to regular pollution events,the frequency of sudden major pollution incidents has increased globally.For simulating the dispersion of pollutants over a large area,the traditional small-scale models are no longer applicable.Moreover,compared with conventional pollutions,sudden pollution incidents provide an updraft for pollutants to start their diffusion and transport from high altitudes,prolonging their retention time in the atmosphere.Thus,the effect of large-size aerosol particles cannot be ignored.But the mesoscale numerical models commonly used in environmental studies at this stage have the problem of insufficient assessment for large particles.In this study,we develop a new module based on the WRF-CMAQ model to establish a sudden pollution assessment system.The global reanalysis data,global sounding and surface observations are used to evaluate the meteorological field of Shaanxi province in 2020simulated by the mesoscale model WRF.The simulation results reproduce the observed data well,and the parameterization scheme in WRF for main physical processes under the meteorological conditions in China is newly developed.Considering the effect of atmospheric advection transport and gravitational sedimentation on the high-throwing large-size particles generated by sudden accidents,the large-particle transport module is developed to simulate the transport path,transport distance and landing point distribution of high-throwing large-size particles,and to study the characteristics of large-particle transport.It is found that large particles are more influenced by gravitational sedimentation,and the main influence distance is about 10-300km.The max transmission distance of particles of 40-80μm is about 780km,which is 4 times of particles of 100-280μm.And for every 2-3km increase in the release height,the concentrated distribution of large-particle transport distance also increases by 20-50km.Dispersion simulation study of pollutants is carried out in the sudden accident pollution assessment system to simulate the diffusion of pollutants and pollution severity and to quantify the influence of multiple emission source characteristics and external environment on the diffusion of pollutants.The range of reasonable emission intensity is 1.2×10³d/s-1.2×10¹⁰d/s for ground emission sources and 1.2×10³d/s-1.2×10¹²d/s for high-altitude emission sources.The multiplicative relationship presented on the pollution degree is consistent with that of the emission concentration.We combine the degree of attenuation of pollutant smoke cloud and the peak concentration of smoke cloud to define a horizontal dispersion area of pollutants.When the concentration of pollutants is attenuated by 80%,the dispersion area of pollutants emitted at high altitude can reach 2000km²,which is about 20 times of pollutants emitted at the surface.Pollutants emitted at high altitude disperse at a max speed of 600km²/h and dissipate at a max speed of 780km²/h.Due to the influence of monsoon and mountainous terrain in southern Shaanxi province,the pollutant dispersion area is the smallest in spring and the widest in winter.The dispersion area in winter when the pollutant concentration decay by 80%is about 7 times of dispersion area in summer and about 20 times of dispersion area in spring and autumn.The dispersion area at 80%pollutant concentration decay in plain terrain varies from about 2 to 8times of that in mountains areas.This sudden accident pollution assessment system could be successfully applied to simulate the dispersion of pollutants generated by sudden accidents under the meteorological conditions in China.