Atmospheric ozone and sulfur dioxide from satellite measurements of backscattered ultraviolet light.

Abstract

An iterative method of estimating total atmospheric O₃ and SO₂ is developed for currently available satellite measurements of backscattered ultraviolet (uv) radiation. This method utilizes a direct inversion of the equation of radiative transfer by using a first order Taylor expansion of this equation with respect to a guessed combination of total O₃ and total SO₂. A new guess is made so as to minimize the difference between the measurements and theoretically calculated values. This method is able to model an atmosphere with molecular scattering or one with scattering by both molecules and particulates. A sensitivity analysis is presented and, in the case of a molecular atmosphere, the errors in retrieved total O₃ are on the order of 20% and for total SO₂ are 25%. Estimates can be performed for an atmosphere containing both molecular scatters and particulate scatters for scattering angles of 110°-150°. In the case of volcanic ash and SO₂ mixed within the stratospheric eruption cloud, retrieval errors for these angles are within the same range as those of the molecular only atmosphere if: the index of refraction of the ash is known to within a factor of 1.5 and the mean radius is also known to within a factor of 2. Application of this method to total ozone measuring spectrometer (TOMS) Nimbus 7 data for scans of a volcanic cloud show the total O₃ amount within the cloud to be noticeably lower than those of positions out of the cloud. This is consistent with the results of others.