Intercomparison of measured and modelled BrO slant column amounts for the arctic winter and spring 1994/95

Abstract

Diurnal variations of the slant column amount of BrO (BrO-SCD) measured at Kiruna/Esrange (67.9°N, 21.1°E) in winter/spring 1994/95 are compared with photochemical calculations using the SLIMCAT model. SLIMCAT assumes a total stratospheric bromine of 20 ppt, JPL-97 kinetics but no tropospheric inorganic bromine. Observed local noon BrO-SCDs are underestimated by the model by 20% to 40%. Sensitivity test of existing uncertainties in the stratospheric chemistry of bromine can not resolve the discrepancy. A tropospheric contribution to the total atmospheric BrO, corresponding to a vertical BrO column of 1 to 2×1013/cm2, (or mixing ratios of 0.75 ppt to 2 ppt assuming an uniform tropospheric height profile) is suggested. Copyright 1999 by the American Geophysical Union.