Ambient Air Hydroxyl Radical Concentrations: Measurements and Model Predictions

This review critically examines the limited number of recent near surface measurements of hydroxyl radicals in urban and rural areas. Predictions of average tropospheric, hemispheric and/or zonal concentrations of hydroxyl radicals derived from methylchloroform and carbon monoxide concentrations and models are discussed. The limitations of one- and two-dimensional model predictions of zonal and seasonal hydroxyl concentrations receive detailed consideration. Of especial concern on a regional scale are cloud cover effects on the penetration of ultraviolet radiation below 320 μm which is critical to the subsequent reactions forming hydroxyl radicals.