Satellite observations of upper stratospheric and mesospheric OH: The HO_xdilemma

Steady-State Distributions of O2 and OH in the High Atmosphere and Implications in the Ozone Chemistry

“…The new HO x mechanisms can therefore provide an explanation for the "ozone deficit" problem (while complementing the reformulated O x cycle 4,5 at the lower altitudes) and simultaneously help to explain the "OH surplus" in the lower mesosphere, an issue that we hope to revisit elsewhere 49 in relation to the so-called "HO x dilemma". 42 Needless to say, the consideration of such mechanisms by no means discards that some downscaling 41 of the rate of O + HO 2 reaction within its error limits may still be useful. 5 …”

On the role of vibrationally excited H2 as a source of OH in the mesosphere

“…Using published rate coefficients for the O( 3 P) + H 2 (v = 1) reaction and altitude profiles of O( 3 P) and H 2 (v = 1), they argued that, at altitudes above 75 km the proposed reaction is as important as the reaction of O( 1 D) atoms with H 2 O in producing OH. They estimated the total OH production from the proposed mechanism to be about 16% at altitudes about 100 km and concluded that the inclusion of this new source of mesospheric OH in current photochemical models may aid in resolving the ''HO x dilemma'' [Conway et al, 2000].…”

Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

“…Therefore, detailed knowledge of OH distribution and variability is needed in order to investigate the terrestrial atmosphere. Nevertheless, until a few years ago there still existed some discrepancies between modelled and measured OH concentration, the so-called HO x dilemma (see Conway et al, 2000), and some uncertainty about its impact on O 3 . The HO x dilemma arises from previous observations of either OH or HO 2 alone which have shown poor agreement with standard chemistry (JPL recommended rates).…”