Study On The Influence Of Boundary Layer Parameterization Schemes On The Simulation Of Meteorological Parameters In The Atmospheric Boundary Layer Under Polluted And Clean Conditions In Beijing

Beijing is the center of Beijing-Tianjin-Hebei region and is the most important political and cultural center in China.Meanwhile,it is one of the most heavily aerosol polluted regions.The topography in Beijing?with mountains to the north and west,and seas to the southeast?impacts the transmission,diffusion and accumulation of pollutants in the complex ways?local atmospheric circulation,boundary layer structure and meteorological parameters distriubution?.The WRF model is one of the most widely used mesoscale meteorological models.The simulation of boundary layer structure and meteorological parameters by different boundary layer parameterization schemes in the model are different.Although there have been many studies on the evaluation of boundary layer parameterization schemes,most of these studies are limited to a short-term process or sunny weather conditions.The simulation of the boundary layer structure and meteorological parameters under polluted and clean conditions is not yet understood.Thus,the WRF model and observed data in Beijing are used to systematically study the influence of the boundary layer structure on air pollution under polluted and clean conditions.And the simulation of boundary layer structure by different parameterization schemes are also investigated.The results suggest:?1?The influence of the near-surface meteorological parameters?relative humidity at 2 m level and wind speed and direction at 10 m level?on PM_2.5 concentrations is greater than the effect of temperature at 2 m level.Regardless of polluted or cleaned conditions,the high PM_2.5concentrations in Beijing are found to be associated with the high relative humidity,small wind speed and the southerly winds.The boundary layer height of the clean condition is greater than the polluted condition whether winter or summer.The low tropospheric stability?LTS?of the polluted condition is greater than that of the clean condition.Eight weather types were defined by the T-PCA method using the relationship between LTS and PM_2.5 concentrations.The 65%of the polluted days are characterized by a high-pressure system located to the southeast of Beijing,which brings southwest winds to Beijing.And the 75%of the clean days by a high-pressure system located to the west and northwest winds are prevailing.It shows that different weather conditions also have a certain impact on the transport and diffusion of pollution.?2?The ACM2 scheme do the best on temperature and relative humidity at 2 m level and wind direction at 10 m level.The MYJ scheme do the best on wind speed in winter,the ACM2scheme performs the best in summer polluted condition and the ACM2 or MYJ scheme behave the best in summer clean days.The PBL schemes have a greater impact on the meteorological parameters than surface layer schemes whether polluted or clean days.The four PBL schemes have the best simulation results on temperature in the vertical direction,which perform the better on relative humidity and wind.?3?The turbulent heat exchange coefficient has a significant daily variation.It is larger during the daytime than nighttime and also larger during clean days than polluted days.The turbulent vertical exchange coefficient of ACM2 scheme has been updated in WRFv3.9,and improve the simulated temperature at 2 m level under clen condition.While there is no significant improvement under the polluted condition.