The Numerical Simulation Of Winter Fog-haze Event In The Eastern China

The accurate representation of the meteorological condition is crucial to the numerical modelling and predicting of the regional fog-haze event,which require appropriate parameterization for planetary boundary layer(PBL)in the model.On the other hand,the aerosols impact on fog formation can be critical in understanding and predicting of fog-haze event.Aerosols not only participate in fog formation by acting as condensation nuclei of droplets but also influence the meteorological factor such as air temperature and moisture,planetary boundary layer height(PBLH)and regional circulation which can favor the fog occurrence.Therefore,the evaluation of PBL schemes and aerosol impacts on fog can not only improve our understanding to the fog-haze progress but also provide references for parameterization schemes in the numerical study of air pollution.The main purpose of this work is to evaluate PBL schemes in simulating the meteorological background and the air quality during the haze event,and to discuss the impacts of the aerosol-radiation interaction(ARI),aerosol-cloud interaction(ARI),BC and non-BC aerosols on the formation of fog.We implement the WRF-Chem model to simulate the haze pollution in the eastern China in December 2013.Four PBL schemes,which include a non-local scheme(YSU)and three local TKE schemes(MYJ,MYNN and BL),are evaluated and compared in representing the haze event.And then,we compare the results from another four parallel experiments that configured with different aerosol effects,to disscuss the roles of aerosol on affecting the fog formation in early December 2013.The main conclusions of this work are as follows:Evaluation over the eastern China shows that the MY-type scheme(MYJ and MYNN2)can provide more accurate meteorological condition in the near surface,while BL shows better performance in representing the aerosol concentration.In Nanjing,PM2.5 concentration in the heavy polluted days are underestimated with large biases,which consequently leads poor performance in simulating the humidity and temperature The relation between the surface pollutant and the ventilation coefficient indicated that the dispersion of the surface pollutant is more efficient when using the non-local PBL scheme YSU,while less efficient with MY-types.Comparation between the observation and simuation shows that the local PBL schemes is suitable for simulating the heavy haze pollution,while the non-local PBL schemes for light to medium pollution.Also,the dispersing of the surface pollutant is less efficient during the heavy pollutions,which indicated the importance of pollutant advection transport to Nanjing.While the investigation of aerosols impact on fog formation shows that the ARI favor the fog formation through cooling the ambient air,increasing the water vapor,and decreasing the PBLH,while the effects of ACI are negligible.Further analyses show that BC plays an important role in intensifying the fog event through a complex process.The dome effect of BC led to an increase of air moisture over sea by reducing PBLH and weakening vertical mixing,which thereby restricts more water vapor in the near surface layer.Then a strengthened daytime onshore flow by a cyclonic wind anomaly,induced by BC heating effect,led to the enhanced moisture advection between sea and land,together with the suppressed PBLH and weakened daytime vertical mixing maintain the high moisture level in the YRD region.Provided with favorable condition,the heavy fog form due to radiative cooling at night in this area,which by definition is an advection-radiation fog.This study highlights the understanding to the different performance of PBL schemes in the predicting of the regional air quality and the importance of anthropogenic emissions in the formation of advection-radiation fog in the polluted coastal areas.