Columnar optical properties of tropospheric aerosol by combined lidar and sunphotometer measurements at Taipei, Taiwan

Vertical extinction profiles and columnar optical properties (optical depth, Angstrom exponent, lidar ratio, and particle depolarization) of aerosols were obtained by simultaneous measurements with a depolarization lidar and a sunphotometer at Taipei, Taiwan from February 2004 to January 2006. Columnar optical depths are high in Feb–Apr (0.61–0.75) by sunphotometer measurements. Lidar measurements show the contribution of aerosols in the free atmosphere on columnar optical depths are about 44–50% in Feb–Apr and about 26–37% in other months. Back-trajectory analyses and depolarization measurements show almost all of non-spherical aerosols originated from Northwest China which indicate Asian dusts frequently transported to Taipei from dust source regions in the free atmosphere. Aerosols with depolarization lower than 5% are found mostly originated from South China or Southeast Asia. Good correlations between columnar lidar ratio, particle depolarization, and Angstrom exponent are found for cases that columnar water vapor less than 1.5 cm. The effect of water vapor on particle depolarization is briefly discussed.