8-year climatology of dust aerosol in the infrared with HIRS Clémence Pierangelo, Alain Chédin, Raymond Armante, Claudia Stubenrauch, and Soumia Serrar Laboratoire de Météorologie Dynamique / IPSL Ecole Polytechnique The last report from the Intergovernmental Panel on Climate Change (IPCC, 2001) pointed out that aerosols are one of the major sources of uncertainty in the climate system. Since then, many studies have been conducted, most of them focusing on the solar spectrum. Yet, the closure of the Earth radiative balance also needs knowledge of the aerosol effect on terrestrial and atmospheric infrared radiation. This is why we focus here on remote sensing of aerosol at infrared wavelengths. We show that it is possible to build an aerosol index over sea using HIRS observations. The algorithm is based on a regression using the brightness temperatures of HIRS channel 8 (11.1 µm) and 10 (8.3 µm) and the sea surface temperature retrieved from TOVS. Great care has been put into discrimination between aerosols and possibly remaining low altitude clouds. Here, we present daily and monthly results over the ocean in the tropics, for the period 1987-1995, both for day-time and night-time observations. Validation with in-situ and satellite retrievals are presently being conducted; moreover, emphasis will be put on the comparison between visible and infrared products. The global coverage of HIRS, the availability of 25 years of observations and the ability to monitor aerosols both during day and night open the way to a very promising archive of mineral aerosol products in the infrared.