Observations of Asian dust and air-pollution aerosols using a network of ground-based Mie-scattering lidars (Invited Paper)

We conduct network observations using ground-based Mie-scattering lidars in Asian region in cooperation with various research organizations and Universities. Primary purpose of the network is for studying generation and transport of Asian dust, observing air pollution and biomass burning aerosols for atmospheric environment studies, observing aerosol vertical distribution and temporal variation for atmospheric radiation studies and climatology, and for validation of chemical transport models and satellite remote sensors. At present, lidars are operated continuously at twelve locations in Japan, China, Korea, and Thailand. The lidars used in the network are two-wavelength (532 nm and 1064 nm) Mie-scattering lidars having depolarization measurement function at 532nm. Flashlamp-pumped compact Nd:YAG lasers are used as the light source. We developed a method for estimating the extinction coefficient of non-spherical air-pollution aerosols separately using the depolarization ratio. This method is based on a simple assumption that observed aerosols are external mixture of two types of aerosols, but it is practically very useful especially for inter-comparison with chemical transport models. We also studied a method for characterizing aerosols using the depolarization ratio and the wavelength dependence of the backscatter coefficient. Asian dust phenomena were observed with the network since spring of 2001. The frequency of the occurrence of dust events and the vertical distribution characteristics were analyzed. Also, seasonal and year-to-year variations were analyzed. At the same time, transport of dust and air-pollution aerosols were studied by comparing the temporal variation of lidar profiles with chemical transport model results.