Abstract
Abstract. The impact and significance of uncertainties in model calculations of stratospheric ozone loss resulting from known uncertainty in chemical kinetics parameters is evaluated in trajectory chemistry simulations for the Antarctic and Arctic polar vortices. The uncertainty in modeled ozone loss is derived from Monte Carlo scenario simulations varying the kinetic (reaction and photolysis rate) parameters within their estimated uncertainty bounds. Simulations of a typical winter/spring Antarctic vortex scenario and Match scenarios in the Arctic produce large uncertainty in ozone loss rates and integrated seasonal loss. The simulations clearly indicate that the dominant source of model uncertainty in polar ozone loss is uncertainty in the Cl2O2 photolysis reaction, which arises from uncertainty in laboratory-measured molecular cross sections at atmospherically important wavelengths. This estimated uncertainty in JCl2O2 from laboratory measurements seriously hinders our ability to model polar ozone loss within useful quantitative error limits. Atmospheric observations, however, suggest that the Cl2O2 photolysis uncertainty may be less than that derived from the lab data. Comparisons to Match, South Pole ozonesonde, and Aura Microwave Limb Sounder (MLS) data all show that the nominal recommended rate simulations agree with data within uncertainties when the Cl2O2 photolysis error is reduced by a factor of two, in line with previous in situ ClOx measurements. Comparisons to simulations using recent cross sections from Pope et al. (2007) are outside the constrained error bounds in each case. Other reactions producing significant sensitivity in polar ozone loss include BrO + ClO and its branching ratios. These uncertainties challenge our confidence in modeling polar ozone depletion and projecting future changes in response to changing halogen emissions and climate. Further laboratory, theoretical, and possibly atmospheric studies are needed.
Highlights
The annual loss of ozone (O3) in the springtime polar lower stratosphere of both hemispheres is a key diagnostic for ozone assessment, recovery prediction, and chemistry interaction with climate change
Quantitative evaluation of chemical uncertainty underlying stratospheric assessment models shows that known uncertainties in kinetic reaction rate parameters from laboratory measurements produce large uncertainty in polar O3 loss calculated in simple, representative models
For both Antarctic and Arctic O3 loss, the Monte Carlo uncertainty distribution is dominated by the recommended JPL06 uncertainty in photolysis cross sections for Cl2O2 at atmospherically relevant wavelengths
Summary
The annual loss of ozone (O3) in the springtime polar lower stratosphere of both hemispheres is a key diagnostic for ozone assessment, recovery prediction, and chemistry interaction with climate change. We compare the results with observations to evaluate which combinations are consistent with atmospheric data This allows us to identify the key reactions and rates contributing the largest potential errors as a guide for future work. We 1) revisit the impact of kinetic uncertainties in models using JPL06 evaluations as well as new lab results (i.e., Pope et al, 2007), 2) assess the impact of constraints on photolysis uncertainty limits provided by atmospheric observations, and 3) identify the major uncertainty sources in simulating polar O3 loss that result from uncertainties in kinetics as a potential guide to further lab measurements. The penultimate section summarizes key rate uncertainties in the polar O3 loss reaction system with potential for future measurement work, and the final section provides summary remarks
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