Analysis of Stratospheric Bromine Monoxide from SCIAMACHY using Comparison with Model Results

Abstract

This thesis presents an analysis of the stratospheric bromine monoxide (BrO) profiles retrieved globally from two years of limb measurements from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography(SCIAMACHY) instrument on board ENVISAT.In order to have a confidence in the quality of the retrieved SCIAMACHY BrO profiles, they need to be validated with BrO measurements, performed using different methods. Hence, as a first step towards a validation of SCIAMACHYBrO retrievals, BrO profiles are compared with the set of balloon-borne BrO measurements. The comparison with a set of four balloon-borne BrO profiles shows mean relative differences in the altitude range from 18 to 30~km between 17% and -42%. In order to validate our current understanding of bromine chemistry, the SCIAMACHY BrO retrievals are compared with modeled BrO profiles, based on estimated inorganic bromine (Bry) from CFC-11 retrievals by the Michelson Interferometer for Passive AtmosphericSounding (MIPAS), also on ENVISAT, and the calculated BrO/Bry ratio from a photochemical model constrained by SCIAMACHY nitrogen di-oxide (NO2) retrievals. The BrO observations are found to be broadly consistentwith our current understanding of stratospheric bromine chemistry and a total stratospheric bromine loading of approximately 18 pptv.Further a global climatology of stratospheric BrO is constructed using the two years' retrievals of BrO. The analysis of SCIAMACHY BrO observations provide for the first time a picture of the seasonal variation of stratospheric BrO on a global scale. At the midlatitudes of both hemispheres BrO shows a strong seasonal cycle with a maximum in winter and a minimum in summer. The seasonal variation of BrO is closely correlated with changes in NO2 in accordance with our present understanding of bromine chemistry.The two years' BrO climatology constructed using the nadir measurements of SCIAMACHY and the climatology constructed in this work is used to calculate the amount of BrO below 15 km in the atmosphere. This calculation shows that aglobal background BrO of 1.4 pptv, averaged over all latitudes and months, exists throughout the year below 15 km in the atmosphere.The knowledge of the total amount of bromine present in the atmosphere is an important issue as it has direct implications on our prediction of the ozone trends. Using the SCIAMACHY BrO observations together with the calculatedbromine partitioning from a photochemical model constrained by the SCIAMACHY NO2 observations, the total stratospheric bromine loading is estimated to be 18.5 /- 4 pptv. This indicates a contribution of about 3.5 /- 4 pptv fromshort lived bromine species in addition to methyl bromide and the halons.