Latitudinal and vertical distribution of bromine monoxide in the lower stratosphere from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography limb scattering measurements
Van Roozendael, M.
von Savigny, C.
Earth and related Environmental sciences
atomic absorption spectroscopy
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Vertical profiles of stratospheric bromine monoxide (BrO) in the 15-30 km range are retrieved from SCIAMACHY limb scatter data over the globe. First validation comparisons with the balloon-borne SAOZ-BrO and LPMA/DOAS instruments indicate retrieval biases of ∼20% or less. Propagated spectral fitting uncertainties lead to a precision approaching ∼25% on a 2 km grid at 25 km. This worsens at higher altitudes because of reduced signal and at lower altitudes because of the reduced penetrability of the atmosphere. In terms of volume mixing ratio (VMR), the single profile precision increases from ∼4 pptv at 17 km to ∼8 pptv at 27 km. Repeatability, an alternative indicator of precision, is 2-3 pptv for SCIAMACHY retrievals and independent of altitude. The BrO stratospheric number density peak generally lies 5 ± 2 km above the tropopause. In the tropics, the stratospheric BrO VMR generally increases with increasing altitude. The observed stratospheric BrO global distribution is generally consistent with previous balloon measurements but does not agree well with results of a model that uses Br
y inferred only from the observed breakdown of long-lived bromoalkanes (i.e., methyl bromide and halons). We find best agreement with the observed vertical and latitudinal distribution of BrO for model results that include an 8.4 ± 2 pptv contribution to stratospheric Br y, most of which is expected from the breakdown of VSL (very short lived) bromocarbons, in addition to the ∼16 pptv contribution from longer-lived sources. This suggests that stratospheric Br y exceeds 20 pptv. Profiles of Br y profiles derived from the balloon measurements of BrO also suggest Br y is in excess of 20 pptv, but the uncertainty and variability of these results do not allow us to definitively rule out this concentration. We find typical BrO VMRs of ∼4 pptv at 15 km in the tropical tropopause layer, suggesting that a significant portion of the bromine from VSL bromoalkane sources may be carried across the tropopause in the form of inorganic decomposition products. We discuss a variety of VSL bromocarbons species that may be contributing to the elevated concentrations of stratospheric BrO.
CitationSioris, C.E.; Kovalenko, L.J.; McLinden, C.A.; Salawitch, R.J.; Van Roozendael, M.; Goutail, F.; Dorf, M.; Pfeilsticker, K.; Chance, K.; von Savigny, C.; Liu, X.; Kurosu, T.P.; Pommereau, J.-P.; Bösch, H.; Frerick, J. (2006). Latitudinal and vertical distribution of bromine monoxide in the lower stratosphere from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography limb scattering measurements. , Journal of Geophysical Research Atmospheres, Vol. 111, Issue 14, D14301, DOI: 10.1029/2005JD006479.