Aerosol Observation with Raman LIDAR in Beijing, China

Aerosol observation with Raman LIDAR in NIES (National Institute for Environmental Studies, Japan) LIDAR network was conducted from 17 April to 12 June 2008 over Beijing, China. The aerosol optical properties derived from Raman LIDAR were compared with the retrieved data from sun photometer and sky radiometer observations in the Aerosol Robotic Network (AERONET). The comparison provided the complete knowledge of aerosol optical and physical properties in Beijing, especially in pollution and Asian dust events. The averaged aerosol optical depth (AOD) at 675 nm was 0.81 and the Angstrom exponent between 440 nm and 675 nm was 0.99 during experiment. The LIDAR derived AOD at 532 nm in the planetary boundary layer (PBL) was 0.48, which implied that half of the total AOD was contributed by the aerosol in PBL. The corresponding averaged LIDAR ratio and total depolarization ratio (TDR) were 48.5sr and 8.1%. The negative correlation between LIDAR ratio and TDR indicated the LIDAR ratio decreased with aerosol size because of the high TDR associated with nonspherical and large aerosols. The typical volume size distribution of the aerosol clearly demonstrated that the coarse mode radius located near 3 ${\mu}m$ in dust case, a bi-mode with fine particle centered at 0.2 ${\mu}m$ and coarse particle at 2 ${\mu}m$ was the characteristic size distribution in the pollution and clean cases. The different size distributions of aerosol resulted in its different optical properties. The retrieved LIDAR ratio and TDR were 41.1sr and 19.5% for a dust event, 53.8sr and 6.6% for a pollution event as well as 57.3sr and 7.2% for a clean event. In conjunction with the observed surface wind field near the LIDAR site, most of the pollution aerosols were produced locally or transported from the southeast of Beijing, whereas the dust aerosols associated with the clean air mass were transported by the northwesterly or southwesterly winds.