Continuous Observations of Aerosol Profiles with a Two-Wavelength Mie-Scattering Lidar in Guangzhou in PRD2006

Abstract

Continuous lidar observation was performed in Guangzhou, China, in the Pearl River Delta (PRD) observation campaign in July 2006 (PRD2006), using a two-wavelength Mie-scattering lidar (532 and 1064 nm) with a depolarization measurement channel at 532 nm. The profiles of the extinction coefficients at 532 nm were derived using the two-wavelength method. The planetary boundary layer (PBL) height and the cloud-base height were derived from the signals at 1064 nm. Two air pollution episodes occurred during the campaign, one on 10?12 July and the other on 22?24 July. Two events with a typhoon-driven flow of northern air occurred on 15 and 25 July. Elevated aerosol layers were observed at 1 km above ground level on 12 July and on 22 and 23 July. This layer was also observed by the lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite (CALIPSO) at 0200 LT 23 July 2006 near Guangzhou. The distribution observed by CALIPSO and trajectory analysis revealed that the layer was probably generated within the PRD region. The time?height indication of the ground-based lidar suggested that aerosols in the elevated layer were transported to the ground by convection when the PBL height reached the elevated layer. The surface concentration of elemental carbon also exhibited a corresponding increase. The air pollution index at Guangzhou, Shaoguan, Changsha, and other cities indicated temporal variations, implying the regional transport of air pollution in the typhoon episodes. Trajectory analysis indicated that an air mass from the north arrived after 24 July in the air pollution episode of 22?25 July 2006.