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Distributions of nitric acid in the troposphere and the stratosphere

Catherine Wespes(1), Daniel Hurtmans(2), Solene Turquety(3), Juliette Hadji-Lazaro(3), Pierre-Francois Coheur(4), Ariane Razavi(2), Cathy Clerbaux(3), Chris Boone(5) and Peter Bernath(6)

(1) Universite Libre de Bruxelles, 50 , Avenue F.D. Roosevelt, 1050 Brussels, Belgium
(2) Universite Libre de Bruxelles, 50, Avenue F.D. Roosevelt, 1050, Brussels, Belgium
(3) Service d'Aeronomie, IPSL, 4 Place Jussieu, 75252 Paris Cedex 05, France
(4) Universite Libre de Bruxelles, 50, Avenue F.D. Roosevelt, 1050 Brussels, Belgium
(5) University of Waterloo, 200 University Avenue W., Waterloo, ON, N2L 3G1, Canada
(6) University of Waterloo, 200 UNiversity Avenue W, Waterloo, ON, N2L 3G1, Canada

Abstract

Reactive nitrogen compounds play an essential role in regulating the chemical composition of the low atmosphere. If the abundances of NO2 in the troposphere are now well monitored from satellite measurements in the UV, there remains significant lack of data regarding both the distributions of other nitrogen oxides (NO, HNO3, PAN) in the troposphere and basically of all NOy compounds at higher altitudes (upper troposphere and stratosphere). Additional HNO3 data, which would improve our understanding of chemical processes in the troposphere and the stratosphere, can be accessed using satellite measurements in the infrared spectral region. In this work we analyze the distributions of HNO3, retrieved from the infrared satellite measurements collected during mission of the Atmospheric Chemistry Experiment (ACE) on the Canadian Scisat satellite, for a two-year period extending from January 2004 to January 2006. The ACE Fourier transform infrared spectrometer operates in solar occultation and delivers highly-resolved vertical profiles for a series of trace gases, from the middle troposphere to the thermosphere. The HNO3 distributions in the upper troposphere and the stratosphere are presented and the seasonal variations are highlighted. The results are discussed by comparison with the distributions of other nitrogen oxides, obtained by the same instrument. A particular emphasis is put on the study of upper tropospheric data, which can be used as indicator of transported pollution and burning plumes. Unfortunately Solar occultation measurements do not allow probing the atmosphere below about 8 km due to the opacity of the lowermost atmospheric layers. Here we show that for HNO3, such measurements can be complemented by nadir soundings in the thermal infrared, which provide HNO3 abundances with some vertical information. For the purpose of illustration, we report on the first global distributions of HNO3 in the troposphere and the stratosphere, obtained from the analysis of measurements by the Interferometric Monitor of Greenhouse Gases (IMG), which operated onboard the ADEOS platform between 1996 and 1997. The results for 10 successive days of IMG operation in April 1997 are discussed.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry