Contrasting the effect of aerosol properties on the planetary boundary layer height in Beijing and Nanjing

The evolution of the planetary boundary layer (PBL) and the effect of aerosols on the PBL in Beijing and Nanjing were compared based on measurements made during two long-term field campaigns. Monthly PBL height (PBLH) trends in Nanjing and Beijing were similar, opposite to those of the mass concentration of particles with diameters less than 2.5 & mu;m (PM2.5). This phenomenon was more obvious in Nanjing than in Beijing. The negative correlation between PBLH and PM2.5 mass con-centration was weaker in Nanjing than in Beijing. The PBLH varied during the day. Heavy aerosol pollution made this variation weak in autumn and winter in Beijing. Further results suggest that out of all the seasons, summertime PM2.5 had the greatest influence on the evolution of the PBL. The PBLH was more sensitive to the variation in PM2.5 mass concentration in Nanjing than in Beijing. Aerosol type (scattering or absorbing) had a weak effect on the evolution of the PBLH in Nanjing, but absorbing aerosols played a dominant role in Beijing. Our results highlight the cross-regional difference in aerosol-PBL interactions.