Global distributions of HO₂NO₂ as observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

Stratospheric and upper tropospheric distributions of peroxynitric acid (HO₂NO₂) were retrieved from limb infrared spectral measurements of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Environmental Satellite (ENVISAT). Single-profile precisions are estimated at 6-14 parts per trillion by volume (pptv) in the altitude range 7-17 km and 19-34 pptv from 17 to 42 km. The vertical resolution is 5 km in the upper tropospheric and stratospheric maxima. Highest stratospheric volume mixing ratios (VMRs) reaching 310 pptv at 27 km are observed at solstice conditions in subtropical latitudes and midlatitudes at the nighttime summer hemisphere, while lowest stratospheric peak VMRs as low as 38 pptv are found during polar winter near the pole. A second maximum in the upper troposphere and lower stratosphere appears from spring to the end of summer with maximum values of 80 pptv between 7 and 14 km. Retrievals based on spectroscopic line list data instead of absorption cross sections produce HO₂NO₂ distributions smaller by a factor of 1.5, on average. Earlier HO₂NO₂ measurements from balloon instruments are in good general agreement with the presented data set if the same spectroscopic data are used. Comparisons of MIPAS HO₂NO₂ distributions to results of the fifth-generation European Centre Hamburg general circulation model/ Modular Earth Submodel System 1 (ECHAM5/MESSy1) provide agreement within 20% if near-infrared photolysis is considered. With the newly available tabulated absorption cross sections and the improved photolysis modeling, former discrepancies between HO₂NO₂ observations and model calculations can be considered to be largely resolved.