Observations of the stratospheric BrO column over Colorado, 40°N

The column abundance of BrO has been measured at 40°N throughout the period from January 22 to May 24, 1993, providing the first remote 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 confirmation provided by the 339‐nm band and by analysis tests showing that spectral overlap with NO 2 does not pose a problem for BrO measurement. The observed slant column abundances showed substantial variability and may be affected in part by heterogeneous chemistry associated with 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.