Seasonal characteristics of lidar ratios measured with a Raman lidar at Gwangju, Korea in spring and autumn

Abstract

Vertical profiles of aerosol lidar ratios at wavelengths of 355 and 532nm were measured with the GIST/ADEMRC (Gwangju Institute of Science & Technology/ADvanced Environmental Monitoring Research Center) multi-wavelength Raman lidar system at Gwangju, Korea (35.10 degrees N, 126.53 degrees E) during several observation periods between February 2004 and May 2005. The total number of observed aerosol layers was 63, of which 38 and 25 were observed in spring and autumn, respectively. Average values of the lidar ratio, Sa, were 55 +/- 10 sr and 56 +/- 9 sr at 355 and 532 nm, respectively, in spring and 61.4 +/- 7.5 sr and 63.1 +/- 12.8 sr at 355 and 532 nm, respectively, in autumn. Cases of high lidar ratio values (> 65sr) were observed more frequently in autumn than in spring for 28% and 46% of the time at 355 and 532nm, respectively. Mean lidar ratio value of 51 +/- 6 sr at 532 nm was obtained for Asian dust particles in spring which was lower than those for non-dust (60 +/- 10 sr) and smoke (65 +/- 8 sr) particles. Very high lidar ratios of 75.3 +/- 15.8 sr at 532 nm were observed above the planetary boundary layer (PBL) in autumn. These high values are believed to have largely resulted from an increased amount of light-absorbing particles mostly in the fine mode of the particle size distribution, generated by coal combustion and agricultural biomass burning. Lidar ratios, Angstrom exponents and effective radii values retrieved from collocated sunphotometer data were similar to those obtained from Raman lidar measurements. (c) 2007 Elsevier Ltd. All rights reserved.