ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-6-3099-2006 A study on aerosol extinction-to-backscatter ratio with combination of micro-pulse lidar and MODIS over Hong Kong He Q. S. 1 Li C. C. 1 Mao J. T. 1 Lau A. K. H. 2 Department of Atmospheric Science, School of Physics, Peking University, Beijing, China The Institute for the Environment, the Hong Kong University of Science and Technology, Hong Kong, China 18 04 2006 6 2 3099 3133 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/6/3099/2006/acpd-6-3099-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/6/3099/2006/acpd-6-3099-2006.pdf

The aerosol extinction-to-backscatter ratio is an important parameter for inverting LIDAR signals in the LIDAR equation. It is also a complicated function of aerosol microphysical characteristics depending on geographical and meteorological conditions. In this paper, a method to retrieve the column-averaged aerosol extinction-to-backscatter ratio by constraining the aerosol optical depths (AOD) recorded by the Moderate Resolution Imaging Spectroradiometer (MODIS) to the ones measured by a Micro-pulse LIDAR (MPL) is presented. Both measurements were taken between 1 May 2003 and 30 June 2004 over Hong Kong, a coastal city in south China. Simultaneous scattering coefficients measured by a forward scattering visibility sensor are compared with the LIDAR retrieval. The data are then analyzed in terms of monthly and seasonal trends. In addition, the relationships between the extinction-to-backscatter ratio and wind conditions as well as other aerosol microphysical parameters are also presented. The mean aerosol extinction-to-backscatter ratio for the whole period is found to be 28.9±6.1 sr, with the minimum of 12 sr in August 2003 and the maximum of 44 sr in March 2004. The ratio is lower in the summer because of the dominance of oceanic aerosols in association with the prevailing southwesterly monsoon. In contrast, relatively larger ratios are noted in spring and winter because of the increased impact of local and regional industrial pollutants associated with the northerly monsoon. The extended LIDAR measurements over Hong Kong provide not only a more accurate retrieval of aerosol extinction coefficient profiles, but also significant information for air pollution and climate studies in the region.