Upper limit for stratospheric HBR using far‐infrared thermal emission spectroscopy

We measure an upper limit for stratospheric HBr from three balloon flights. The observations were made with the FIRS‐2 far‐infrared Fourier transform spectrometer. The 1σ upper limits from the 1988, 1989 and 1990 balloon flights are 13 pptv at 35 km, 7 pptv at 32 km, and 3 pptv at 31 km, respectively. Combining all 3 flights, the weighted average 1σ upper limit for HBr is 4 pptv at 32 km. This value is significantly smaller than the only other previously published spectroscopic value of 20 ± 7 pptv (2σ), but is consistent with (albeit well in excess of) a theoretical estimate which predicts roughly 0.4 pptv at this altitude.