Stratospheric NO and NO_2 abundances from ATMOS Solar-Occultation Measurements

Abstract

Using results from a time-dependent photochemical model to calculate the diurnal variation of NO and NO_2, we have corrected Atmospheric Trace MOlecule Spectroscopy (ATMOS) solar-occultation retrievals of the NO and NO_2 abundances at 90° solar zenith angle. Neglecting to adjust for the rapid variation of these gases across the terminator results in potential errors in retrieved profiles of ∼20% for NO_2 and greater than 100% for NO at altitudes below 25 km. Sensitivity analysis indicates that knowledge of the local O_3 and temperature profiles, rather than zonal mean or climatological conditions of these quantities, is required to obtain reliable retrievals of NO and NO_2 in the lower stratosphere. Extremely inaccurate O_3 or temperature values at 20 km can result in 50% errors in retrieved NO or NO_2. Mixing ratios of NO in the mid-latitude, lower stratosphere measured by ATMOS during the November 1994 ATLAS-3 mission compare favorably with in situ ER-2 observations, providing strong corroboration of the reliability of the adjusted space-borne measurements.