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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. [Copyright &y& Elsevier]

Abstract: Metropolitan Taipei, which is located in the subtropical area, is characterized by high population and automobile densities. For convenience, most primary schools are located near major roads. This study explores the exposure of acid aerosols for schoolchildren in areas in Taipei with different traffic densities. Acid aerosols were collected by using a honeycomb denuder filter pack sampling system (HDS). Experimental results indicated that the air pollutants were significantly correlated with traffic densities. The ambient air NO2, SO2, HNO3, NO3 −, SO4 2−, and aerosol acidity concentrations were 31.3 ppb, 4.7 ppb, 1.3 ppb, 1.9 μg m−3, 18.5 μg m−3, and 49.5 nmol m−3 in high traffic density areas, and 6.1 ppb, 1.8 ppb, 0.9 ppb, 0.7 μg m−3, 8.8 μg m−3 and 14.7 nmol m−3 in low traffic density areas. The exposure levels of acid aerosols for schoolchildren would be higher than the measurements because the sampling height was 5 m above the ground. The SO2 levels were low (0.13–8.03 ppb) in the metropolitan Taipei. However, the SO4 2− concentrations were relatively high, and might be attributed to natural emissions of sulfur-rich geothermal sources. The seasonal variations of acid aerosol concentrations were also observed. The high levels of acidic particles in spring time may be attributed to the Asian dust storm and low height of the mixture layer. We conclude that automobile contributed not only the primary pollutants but also the secondary acid aerosols through the photochemical reaction. Schoolchildren were exposed to twice the acid aerosol concentrations in high traffic density areas compared to those in low traffic density areas. The incidence of allergic rhinitis of schoolchildren in the high traffic density areas was the highest in spring time. Accompanied by high temperature variation and high levels of air pollution in spring, the health risk of schoolchildren had been observed. [Copyright &y& Elsevier]

The optical properties (extinction-to-backscatter ratio, backscattering, depolarization, and backscatter-related Angstrom exponent) and height distribution of Asian dusts were measured using a two-wavelength Raman/depolarization lidar at Taipei, Taiwan, during the Asian dust seasons in 2004 and 2005. Dust layers were frequently observed in the free atmosphere (1–6km). Dust optical thickness ranged from 0.01 to 0.55; backscatter-related Angstrom exponents ranged from 0.42 to 1.47; and lidar ratios (extinction-to-backscatter ratio) for 355nm ranged from 32 to 72sr (steradian). The mean values of dust particle depolarization and extinction coefficient are and , respectively, which are close to the moderate dust depolarizations and extinctions observed in free atmosphere in China and Japan. Backscatter-related Angstrom exponents were found correlated positively with lidar ratio and negatively with particle depolarization, indicating that the dust optical characteristics are predominated by size distribution. Dusts were found to tend to exhibit unusual low depolarization properties under moist conditions (relative humidity ), and the possible explanations are discussed. [Copyright &y& Elsevier]