A study on the aerosol extinction-to-backscatter ratio withcombination of micro-pulse LIDAR and MODIS over Hong Kong

[摘要] The aerosol extinction-to-backscatter ratio is an important parameter forinverting LIDAR signals in the LIDAR equation. It is a complicated functionof the aerosol microphysical characteristics. In this paper, a method toretrieve the column-averaged aerosol extinction-to-backscatter ratio byconstraining the aerosol optical depths (AOD) from a Micro-pulse LIDAR (MPL)by the AOD measurements from the Moderate Resolution ImagingSpectroradiometer (MODIS) is presented. Both measurements were taken oncloud free days between 1 May 2003 and 30 June 2004 over Hong Kong, acoastal city in south China. Simultaneous measurements of aerosol scatteringcoefficients with a forward scattering visibility sensor are compared withthe LIDAR retrieval of aerosol extinction coefficients. The data are thenanalyzed to determine seasonal trends of the aetrosolextinction-to-backscatter ratio. In addition, the relationships between theextinction-to-backscatter ratio and wind conditions as well as other aerosolmicrophysical parameters are presented. The mean aerosolextinction-to-backscatter ratio for the whole period was found to be29.1±5.8 sr, with a minimum of 18 sr in July 2003 and a maximum of 44 srin March 2004. The ratio is lower in summer because of the dominance ofoceanic aerosols in association with the prevailing southwesterly monsoon.In contrast, relatively larger ratios are noted in spring and winter becauseof the increased impact of local and regional industrial pollutantsassociated with the northerly monsoon. The extended LIDAR measurements overHong Kong provide not only a more accurate retrieval of aerosol extinctioncoefficient profiles, but also significant substantial information for airpollution and climate studies in the region.

[学科分类] 大气科学