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Upper Tropospheric Composition Measurements with ACE-FTS: HNO3 and C2H4

C Wespes(1), P.F. Coheur(1), H Herbin(1), D Hurtmans(1), L Clarisse(1), M George(2), C Clerbaux(2), C.D. Boone(3) and P.F. Bernath(4)

(1) SCQP/ULB, Spectroscopie de l'Atmosphere, 1050 Brussels, Belgium
(2) UPMC Univ. Paris 06, CNRS UMR8190, LATMOS/IPSL, 75005 Paris, France
(3) University of waterloo, Department of Chemistry, N2L 3G1 Ontario, Canada
(4) University of York, Department of chemistry, YO10 5DD York, United Kingdom

Abstract

The ACE-FTS instrument onboard Scisat-1 is designed primarily to monitor the composition of the stratosphere at high northern latitudes, with the objective to improve upon our understanding of the physical and chemical processes driving ozone chemistry in these regions. Here we exploit the high sensitivity of the solar occultation observing mode along with the exceptional performances of the infrared FTS to probe minor tropospheric species in the upper troposphere.

The results include quasi-global distributions of tropospheric nitric acid acquired during a two years period (February 2004 to Augustus 2006) of the ACE-Scisat mission. Latitudinal and seasonal trends exhibiting a strong North-South gradient are provided and analyzed in regard to the strength of the relationship with ozone. Information on different NOx oxidation pathways in the troposphere and the stratosphere are put in perspective through a detailed comparative study of the HNO3-O3 correlations between both layers. We also show measurements of PAN and other NOy for two selected occultations representative of biomass burning plume and lightning sources.

Other results are presented for ethene (C2H4), which is a shorter lived species, with sources from biomass burning or anthropogenic activities. Zonal distributions and vertically resolved latitudinal distributions are derived for a two year period analyzed (2005-2006), highlighting spatial – including a North-South gradient - as well as seasonal variations. We show the latter to be more pronounced at the highest latitudes, presumably as a result of less active photochemistry during winter. The observation of C2H4 enhancements in remote Arctic regions at high latitudes is consistent with the occurrence of fast transport processes of gaseous pollution from the continents leading to Arctic haze, opening perspectives for a better quantification of the contribution of short-lived organic species in the pollution of these remote regions.