Aircraft study of aerosol vertical distributions over Beijing and their optical properties

A set of 152 vertical profiles of aerosol number concentration and size distribution with diameter ranging from 0.12 to 3.0 mu m observed by the airborne optical spectrometer probe in Beijing, China, between February 2005 and September 2006 is analysed and discussed. The statistic of aerosol number concentration (N-a) reveals a high aerosol number density in this region with average surface level number concentration (N-0) of about 6600 cm-3 (0.12-3.0 mu m). The average vertical profile of N-a approximately satisfies an exponential decline function with a scale height of 1419 m. The N-a profiles are influenced by the structures of planetary boundary layer (PBL) significantly and two typical types of N-a profile under different conditions of PBL are presented and parametrized in this study. The observations of aerosol size distribution show that, in most cases the aerosol size distributions are not very sensitive to altitude, with effective radii ranging from 0.16 to 0.28 mu m. Comparison between aircraft-derived aerosol optical depth (AOD) and Moderate Resolution Imaging Spectroradiometer-derived AOD shows good agreement. The Mie model calculations suggest that the surface level number concentration, the PBL height and the structure of PBL can influence the AOD significantly.