EOS Validation Program

Institution: University of Colorado
Phone: (303) 492-3179
E-mail: margaret.tolbert@colorado.edu

Brian Toon, University of Colorado

September 2001

Atmospheric aerosols can have an important influence on the Earth's radiation budget and can impact the chemical composition of the atmosphere through heterogeneous chemical reactions. To accurately include aerosol effects into atmospheric models, it is necessary to obtain information on aerosol composition, abundance and size distribution. Several EOS instruments are planned which could provide this important aerosol data through infrared measurements. Specifically, HIRDLS and TES on the CHEM platform and AIRS and MODIS on the AM/PM platforms all have infrared regions that can be used to determine aerosol properties. HIRDLS has 21 channels in the infrared ranging from 6.12 to 17.763 mm, while TES provides continuous infrared coverage from 2.3 to 15.4 mm. AIRS has 2300 channels ranging from visible wavelengths at 0.4 mm to infrared wavelengths at 15.4 mm. MODIS has 15 bands in the infrared range of 3 to 14.5 mm. To extract aerosol properties from these instruments, it is vital to have accurate infrared optical constants of relevant aerosol materials. Our EOS investigation includes three tasks related to the optical constants of atmospheric aerosols. First, we will measure the infrared optical constants of ice, sulfuric acid, ammonium sulfate solutions, and various nitric acid/sulfuric acid/water solutions. Our measurements will span the range of temperatures found in the atmosphere, the range of solution concentrations likely to occur in the atmosphere, and a broad range of infrared wavelengths. Second, we shall explore the reasons that various measurement techniques might produce different results for the optical constants. Finally, we will develop an interpolation technique so that the optical properties of the aerosols at a given temperature and solution concentration can be obtained from data which is measured on a sparse grid of temperatures and concentrations.