OBSERVATIONS OF THE STRATOSPHERIC BRO COLUMN OVER COLORADO, 40-DEGREES-N

The column abundance of BrO has been measured at 40-degrees-N througho ut the period from January 22 to May 24,1993, providing the first remo te sensing observations of this key molecule at midlatitudes. The near -ultraviolet BrO absorption bands at 349 and 355 nm have been clearly identified in the measured scattered sky spectra, with additional conf irmation provided by the 339-nm band and by analysis tests showing tha t spectral overlap with NO2 does not pose a problem for BrO measuremen t. The observed slant column abundances showed substantial variability and may be affected in part by heterogeneous chemistry associated wit h Pinatubo aerosols. The zenith angle dependence and magnitude of the slant column measurements indicate that the bulk of the BrO is located near 15-20 km and that the mixing ratio there is of the order of 5-8 parts per trillion by volume.