A measurement of stratospheric HO2 by ground‐based millimeter‐wave spectroscopy

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Abstract
We have measured stratospheric perhydroxyl (HO2) by using a sensitive mm‐wave receiver to obtain spectroscopic line profiles of three rotational emission lines in the vicinity of 265.8 GHz. The observations were carried out over four days in September–October 1982 at Mauna Kea, Hawaii (19.5 N latitude) and yield good agreement with the column density and vertical distribution predicted above ∼35 km by three representative two‐dimensional photochemical models employing JPL 82‐57 reaction rates and chemistry; predictions from the same models using WMO/NASA chemistry yield poor agreement with our observations. Contrasts between current theoretical predictions and previous observations by Anderson et al. are pointed out for HO2 in the 28 to 37‐km range, along with the difficulty of joining the latter with our own measurements through a monotonically varying vertical profile for HO2. A possible explanation involving strong temporal and spatial variation in stratospheric water vapor content is suggested.