Comparing atmospheric [HO2]/[OH] to modeled [HO2]/[OH]: Identifying discrepancies with reaction rates

Reactions that inter-convert OH and HO2 are directly involved in the cataly tic removal of O-3 in the lower stratosphere and in the catalytic productio n of O-3 in the upper troposphere. The agreement between the measured and m odeled [HO2]/[OH] tests our current understanding of this important chemist ry. Recent changes to the recommended rate constants for OH+O-3 and HO2+O-3 call into question how accurately the chemistry of the stratosphere is und erstood. [HO2]/[OH] calculated with the new recommendations is 48% higher t han the observations throughout the lower stratosphere, exceeding the uncer tainty limits of the observations (20%). The extensive atmospheric data set allows tests of the rates of the individual processes that couple these fr ee radicals. This work shows that the discrepancy is largest when the ratio is controlled by the reactions of OH and HO2 with ozone.