Contrasting The Effect Of Aerosol Properties On The Planetary Boundary Layer Height In Beijing And Nanjing

The height of planetary boundary layer（PBLH）has an important effect on the development and evolution of cloud,convection and atmospheric pollution.However,few experiments have been conducted to continuously measure the atmospheric boundary layer height over a long period time,and the influence mechanism of urban particles with diameters less than 2.5μm(PM_2.5)physical and chemical properties on the PBLH under different regional backgrounds is still unclear.Beijing-Tianjin-Hebei and Yangtze River Delta are the two major urban agglomerations in China.Beijing and Nanjing are the representative cities of Beijing-Tianjin-Hebei and Yangtze River Delta respectively.In this study,a long-term Atmosphere–Aerosol–Boundary Layer–Cloud Interaction Joint Experiment was conducted in these two cities respectively.The variation of PBLH in different regions and the influence mechanism of physical and chemical properties of PM_2.5on PBLH were analyzed.The results show that the atmospheric boundary layer height in Beijing is significantly lower than that in Nanjing,and the monthly variation trend is the same.For the PBLH in summer,Beijing is about 200m lower than Nanjing on average,while the PM_2.5mass concentration in Beijing is higher than that in Nanjing.Meanwhile,the diurnal variation of PM_2.5mass concentration has a great influence on the diurnal variation of PBLH.There is a strong interaction between PBLH and PM_2.5concentration.The increase of PM_2.5mass concentration leads to the reduction of solar radiation,which inhibits the development of the planetary boundary layer（PBL）,which further inhibits the convergence of low-level aerosols,resulting in a higher PM_2.5mass concentration.The results show that there is a nonlinear inverse correlation between PBLH and PM_2.5mass concentration.PM_2.5has a significant effect on the evolution of PBL.The development of the daytime PBL under the condition of low PM_2.5mass concentration is more intense than that under the condition of high PM_2.5mass concentration.The comparison of the two seasons shows that the PM_2.5mass concentration in spring and winter is more sensitive to PBL development.Compared with Nanjing,the PBLH in Beijing varies less with PM_2.5mass concentration in different seasons,but the correlation is better.By comparing and analyzing the relationship between r BC and PBLH,the ratio of the scattering aerosol mass concentration and black carbon（BC）mass concentration in the two regions is concluded:Aerosol type（scattering or absorbing） had a weak effect on the evolution of the PBLH in Nanjing,but absorbing aerosols played a more dominant role in Beijing.