Uncertainty Evaluation Of Boundary Layer Schemes And Study Of Surface Layer Parameterization In Haze Simulation

As an ambient air layer for human beings,the planetary boundary layer(PBL),especially the surface layer,plays an important role in the formation,accumulation,and removal of air pollutants in the atmospheric environment directly affecting air quality changes.It is found that the air flow in the PBL is always in a turbulent state.Thus,the PBL and its parameterization have always been difficult problems in evaluation and forecast of atmospheric environmental changes.Focusing on this atmospheric environmental science problem,this thesis is mainly based on the atmosphere chemical models to evaluate the uncertainties of the PBL schemes in haze simulation and then introduce a new surface layer scheme and discuss its performance of turbulent flux calculation in the PBL.The main study contents and conclusions are summarized as follows:1)Simulation analysis of meteorological-environmental elements in the PBL for haze pollutionThe atmosphere chemical model GRAPES_CUACE was used to simulate the PM2.5 concentrations and the conventional meteorological elements of the PBL in Beijing-Tianjin-Hebei region from December 13,2016 to January 14,2017 with the validation on the simulation results by commonly statistical tests.The results show that the model could reasonably simulate the changing patterms of meteorological-environmental elements,but there are the discrepancies between simulations and observations,especially in haze pollution with,the large simulation bias of PM2.5,which could be resulted from the uncertainties of the PBL simulation.2)Assessments of simulated PM2.5 in different boundary layer schemesThree boundary layer schemes MRF,MYJ,and YSU,commonly used in the model were selected to evaluate the performances on simulation of PM2.5 and meteorological elements of the PBL during haze a pollution event over December 16-21,2016.The results show that all the three schemes had underestimated the PM2.5 concentrations to varying degrees,and there is no clear distinction between the simulations in day and night during the pollution period.In general,the YSU scheme has the best simulation ability.The MYJ scheme presents the most underestimate.The meteorological elements of the PBL simulated by three schemes are different from each other.For near-surface wind speeds,the results of the MRF and YSU schemes are generally better than that of the MYJ scheme;for the near-surface air temperature and relative humidity,the results of the MYJ scheme are closer to the observed values.This shows that,in addition to the PBL schemes,the parameterization of the turbulent flux in the surface layer is an important factor affecting the PBL structure in the model.3)Introduction of a new surface layer scheme for the simulation of turbulent fluxesA new surface layer scheme(Li scheme)was introduced to simulate turbulent fluxes.Based on the observational data from the Gucheng station in Hebei province,the offline comparison test between the Li scheme and the classic MM5 scheme was conducted.The results show that,firstly,the aerodynamic roughness length z0m and the thermal roughness length z0h、have important effects on turbulent flux calculation with,the distinguished differences between two schemes.Secondly,the Li scheme in the algorithm could make the improvement of the simulation of momentum and sensible heat flux compared the MM5 scheme in.During the pollution period,the simulation results of momentum and sensible heat flux by the Li scheme are overall better than the MM5 scheme.Especially in stage of PM2.5 accumulation,corresponding the change from unstable to stable,the advantages of Li scheme is more prominent.The performance of the new scheme provides a theoretical basis for online coupling into atmosphere chemical models in the future improving the accuracy of air quality forecast.