Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case sudy on 23 April 1996

Abstract

The vertical distributions of tropospheric aerosol properties were measured during the Asian dust event over central Japan (35°-36°N, 136°-137°E), using a ground-based Raman lidar and aircraft-based instruments on 23 April 1996. The lidar measured enhancements of aerosol backscattering below an altitude of 4 km and between 5 and 8 km where the total aerosol linear depolarization ratio showed peaks of 12-15% and the relative humidities were ∼30%. The aircraft measurements showed that the aerosol particles consisted primarily of irregularly shaped mineral dusts and sea salts with a mode radius (r m) of ∼1 μm and sulfates with r m ∼ 0.1 μm over the measured height range of 0.6-5.5 km. Electron microscopic analyses suggest that ∼77% of the mineral particles were coated with a solution at 1.8 km and that the fraction of coated particles decreased with height. The aerosol backscattering coefficients (β a), calculated from the airborne optical particle counter (OPC) data, were smaller than the lidar-derived values by ∼30% above 3.1 km and by ∼44% below that altitude. The difference was attributable to the horizontal and temporal inhomogeneities of the aerosol properties between the measurement sites and to the uncertainty in β a, particularly for the coarse particles calculated from the OPC data. The aerosol depolarization ratios (δ a) estimated from the OPC data showed the same increase as those obtained with the lidar above 4.1 km. This suggests that the proportion of backscattering by coarse particles to total particles primarily controlled the δ a measured with the lidar in that region.