Measuring and modeling the tropospheric hydroxyl radical (OH)

Efforts to measure the tropospheric hydroxyl radical concentration OH, began 20 yr ago. New measurements put constraints on photochemical models that compute OH and other species. Reproducing observed OH with a model is more successful in some regimes than in others with calculated OH usually within 20% of measurements. This paper reviews OH photochemistry, comparisons of model-derived and measured OH in the continental boundary layer, and model calculation of OH in the marine boundary layer and free troposphere when high-frequency aircraft measurements of O₃ and related trace gases are assimilated into a photochemical model. Factors affecting model calculations of OH - nonlinearities, imprecisions in kinetics, differences among model formulation - are also discussed. -from Author