Technical Note: Evaluation of simultaneous measurements of mesospheric OH, HO2, and O3 under photochemical equilibrium assumption: Statistical approach.

The Technical Note presents a statistically correct approach to evaluating simultaneous measurements of several atmospheric components under the assumption of photochemical equilibrium. We consider simultaneous measurements of OH, HO₂, and O₃ at the altitudes of the mesosphere as a specific example and their daytime photochemical equilibrium as an evaluating relationship. A simplified algebraic equation relating local concentrations of these components in the 50-100 km altitude range has been derived. The parameters of the equation are air temperature, air concentration, local zenith angle, and the rates of 9 reactions. We have performed one-year simulation of the mesosphere and lower thermosphere using a 3D chemical-transport model. The simulation shows that the discrepancy between the calculated evolution of the components and the equilibrium value given by the equation does not exceed 3-4 % in the full range of altitudes independent of season or latitude. We have developed the technique of statistic Bayesian evaluation of simultaneous measurements of OH, HO₂ and O₃ based on the equilibrium equation taking into account the measurement error. The first results of application of the technique to MLS/Aura data are presented in this Technical Note. It has been found that the satellite data of HO₂ distribution regularly demonstrates essentially lower altitudes of mesospheric maximum of this component. This has also been confirmed by offline retrieval of HO₂ from the MLS primary data. [ABSTRACT FROM AUTHOR]