ON THE HO2- ITS MISAPPLICATION IN ATMOSPHERIC CHEMISTRY MODELS(HO2 REACTION )

The self-reaction of the HO2 radical is an important termination react ion for HOx and it is the major gas phase source of hydrogen peroxide in the atmosphere. It is well established that the rate of this reacti on is sensitive to both pressure and water vapor concentrations. The N ASA recommended rate parameter (DeMore et al., 1992) has been utilized in several detailed gas phase chemical mechanisms for modeling the tr oposphere, but several other recent studies have omitted one or both o f the terms for the rate constant. If both the pressure and the water dependent terms are omitted the relative error can be as high as 75% a t the surface to near 30% at 10 km for water vapor saturated condition s. Models which omit these terms will predict incorrect HOx budgets, u nderestimate gas phase hydrogen peroxide formation rates, and overesti mate ozone and organic peroxide formation rates especially in clouds o r under marine conditions.