Investigation of high spectral resolution signatures and radiative forcing of tropospheric aerosol in the thermal infrared

Tropospheric aerosol is well known to affect the transport of radiant energy through the atmosphere, thereby impacting the radiative balance and climate of the Earth along with remote sensing of geophysical properties. Significant research and optical modeling has been conducted for aerosol in the solar regime, but little work has been done to date in the thermal infrared, especially at high spectral resolution.;In this dissertation we begin to address these issues in a number of ways. First, we have developed a high spectral resolution library of atmospheric aerosol optical constants to support advanced modeling of optical properties. As part of this effort we have developed new optical constants from attenuated total reflectance measurements of sulfate-nitrate-ammonium aqueous solutions. We also collected a broad range of existing optical constants for aerosol components including numerous mineral optical constants.;The mineral optical constants were used to model and study infrared dust optical signatures as a function of the composition, size, shape and mixing state. This analysis indicated that the non-sphericity of naturally-occurring dust particles must be taken into account when modeling dust optical properties at high spectral resolution in the thermal infrared (IR). Our modeling indicated that the T-matrix method was a good candidate for more accurate modeling. Our new results provide insight into how optical signatures could be used to retrieve dust microphysical properties. We also examined the performance of some of the most common effective medium approximations for internal mixtures by using them to model the optical constants of our newly determined sulfate-nitrate-ammonium mixtures.;The knowledge gained from the optical signature analysis was applied to airborne and satellite high spectral resolution thermal infrared radiance data impacted by Saharan dust events. The spectral signature of these actual dust events confirmed that the non-spherical nature of dust particles must be taken into account and that the use of Mie theory for dust optical modeling is not valid at in the thermal IR. Using T-matrix calculated optical properties we developed a new technique to retrieve dust microphysical properties from the dust spectral signature. We also retrieved dust microphysical properties using a standard dust optical constants dataset based on bulk sample measurements, and noted significant differences in the retrieved dust microphysical properties.;Lastly, we used the microphysics retrieved from our new technique and from the standard approach to investigate the effects of dust on radiative forcing and cooling rates in the thermal IR. We demonstrate substantial differences in the retrieved properties. More critically though, we observed significant differences in radiative forcing and cooling rates when the microphysics from the standard dust model were used in a model based on a mixture of the individual mineral components.;This work demonstrates that the determination of, or correction for, dust radiative effects and the retrieval of dust microphysical properties in the thermal IR must begin with accurate modeling of dust optical properties at high spectral resolution that properly takes into account the composition, shape and size distribution of the dust particles. Doing so will allow for more accurate and consistent quantification of dust climate impacts between measurements and models.