Temperature Dependent Absorption Cross-Sectionsof O3 and NO2 in the 240 - 790 nm range determined by using the GOME-2 Satellite Spectrometers for use in Remote Sensing Applications

Abstract

Absorption spectra of O3 and NO2 have been measured in three independent campaigns using the three highly stabilized and accurately characterized GOME-2 satellite spectrometers,flight models FM2, FM2-1, and FM3.GOME-2 (Global Ozone MonitoringExperiment) is an enhanced follow-up project of GOME, which was launched on ESA's second European Remote Sensing Satellite (ERS-2) in 1995.A new generation of satellites for earth observation will be available with the MetOp series, starting most likely in the second half of 2006. MetOp comprises three polar-orbitingsatellites to be launched sequentially over 14 years. One of the operational instruments onboard these satellites will be GOME-2, a nadir-viewing spectrometer that observes solarradiation transmitted or scattered from the Earth atmosphere or from its surface.Spectra were recorded at five temperatures (203 K, 223 K, 243 K, 273 K, and 293 K) for O3 and four temperatures (223 K, 243 K, 273 K and 293 K) for NO2 with a spectralcoverage of 240 to 790 nm at a resolution of 0.24 to 0.53 nm full width at half maximum.The relative temperature dependences were determined.The achieved set of laboratory measurements of O3 absorption spectra is in very good agreement (about 1-3 % at 293 K) with the recommended O3 absorption cross sectionsat 10 different wavelengths. For the temperature dependence in the range of 400 to 450 nm an upper limit estimate of no more than 10 % decrease with falling temperature wasfound at 425 to 430 nm in disagreement with one previous publication. There is some evidence that continuous absorption as measured in the blue wing of the Chappuis bandat 429.5 nm drops by a few percent when temperature is reduced from 293 K to 203 K.At the same time the peak of the band at 426.5 nm increases slightly by approx. 1 %. This is supported by a clear increase of amplitude of differential absorption cross section at 426nm of 13 % with falling temperature. At 604.61nm at the top of the Chappuis band a slight increase of cross section with falling temperature of approx. 1 % is found in agreementwith three previous publications and in disagreement with one most recent one.The measurements of NO2 absorption spectra are in very good agreement with literature data and recommended NO2 absorption cross sections at ambient temperature (about 1-2% in the main DOAS window between 400 and 500 nm). The determined temperature dependence is in agreement with previous observations, i.e. a linear increase of the peak-to-valley absorbance difference with decreasing temperature from 293 K to 223 K.The purpose of this study is mainly focused on the clarification of the above mentionedopen issues regarding the O3 absorption cross sections.Nevertheless both sets of newly achieved absorption spectra of O3 and NO2 are of high importance as reference data for remote sensing, and will be used to derive (withGOME-2) a detailed picture of the atmospheric content and profile of O3, NO2 and othertrace gases. It will furthermore help to validate and improve the spectroscopic database.