Vertical distribution of water-soluble, sea salt, and dust aerosols in the planetary boundary layer estimated from two-wavelength backscatter and one-wavelength polarization lidar measurements in Guangzhou and Beijing, China

Vertical and temporal distributions of water-soluble, sea salt, and dust aerosols in the planetary boundary layer (PBL) were analyzed from two-wavelength (532 and 1064 nm) backscatter and one-wavelength (532 nm) polarization lidar measurements taken at Guangzhou in July 2006 and Beijing in August 2006. We used an algorithm that estimates the extinction coefficients for each aerosol component from the three-channel lidar data. The results revealed water-soluble aerosols, most of which were anthropogenic aerosols, were dominant in both cities. Air pollution events occurred on 12 and 22–24 July in Guangzhou and on 3–11, 16–19, and 23–25 August in Beijing. Differences in temporal variation of extinction coefficient of water-soluble particles (σWS) in the lower layers during the air pollution periods were distinct: σWS was higher in the nighttime at Beijing, whereas σWS was higher in the daytime in Guangzhou. Meanwhile similar vertical structures of σWS in the planetary boundary layer were found for both cities: σWS increased as the altitude increased. We suggest that different mechanisms contributed to the temporal and vertical variations of σWS in each city: hygroscopic growth mainly enhanced σWS in the nighttime and at high altitude for Beijing, while the transport of aerosols in the local area mainly enhanced σWS in the daytime and at high altitude in Guangzhou. Distinct differences were also observed in the sea-salt components in Guangzhou and in the dust components in Beijing. The correlation of the dust concentration and aerosol depolarization ratio implies that internal mixing of water-soluble and dust particles occurred in Beijing during the air pollution periods.