The NASA ER-2, an atmospheric sensing version of the US Air Force U-2, has been used in many measurement campaigns since the mid-1980s to probe the chemistry and dynamics of the lower stratosphere using suites of miniaturized instruments. The Composition and Photodissociative Flux Measurement (CPFM) spectroradiometer was added in 1992 primarily for the direct calculation of photolysis rate coefficients. The CPFM, installed on the right wing, measures the downwelling spectral irradiance, two linear polarizations of limb radiance at ten locations about the limb, and two linear polarizations of the nadir radiance from 300-770 nm at 1 nm resolution. The focus of this dissertation has been the inversion of CPFM spectroscopic measurements towards the retrieval of aerosols and trace gases (ozone, NO₂, and BrO). To this end, a radiative transfer model with polarization has been developed. Several flights from the recent (April-September 1997) Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) campaign have been analyzed.

         In an effort to ascertain what aerosol properties might be retrieved from CPFM measurements, a study was undertaken to quantify the sensitivity of limb radiance and polarization at different wavelengths to changes in aerosol number density, size, and refractive index. It revealed that the limb radiances are best suited to the recovery of the aerosol extinction coefficient profile information. However, due to the geometry, only limited vertical information is available and so a parameterized extinction coefficient profile was suggested for use in the retrieval. Polarization was found to be useful for the retrieval of aerosol effective radius and to a lesser extent effective variance, but appears insensitive to refractive index. A simple retrieval technique was devised based on these results.

         Vertical column abundances and profile information about ozone, NO₂, and BrO have been retrieved using the method of Differential Optical Absorption Spectroscopy (DOAS) combined with results from the radiative transfer model. The DOAS spectral fitting was successful for all three species and particularly ozone. The agreement of the retrieved column abundances with the limited number of sources available for comparison varied considerably. The most important result of this work was the observation of large BrO column abundances in the Arctic troposphere during a flight from 26 April 1997. Three flights made in May 1997 also revealed enhanced tropospheric BrO. These results have implications on the current understanding of the horizontal and vertical extent of tropospheric BrO that may also effect the polar tropospheric ozone budget.

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