Abstract:
Stratospheric solar geoengineering (SG) would impact ozone by heterogeneous chemistry. Evaluating these risks and methods to reduce them will require both laboratory and modeling work. Prior model-only work showed that CaCO
3 particles would reduce, or even reverse ozone depletion. We reduce uncertainties in ozone response to CaCO
3 via experimental determination of uptake coefficients and model evaluation. Specifically, we measure uptake coefficients of HCl and HNO
3 on CaCO
3 as well as HNO
3 and ClONO
2 on CaCl
2 at stratospheric temperatures using a flow tube setup and a flask experiment that determines cumulative long-term uptake of HCl on CaCO
3. We find that particle ageing causes significant decreases in uptake coefficients on CaCO
3. We model ozone response incorporating the experimental uptake coefficients in the AER-2D model. With our new empirical reaction model, the global mean ozone column is reduced by up to 3%, whereas the previous work predicted up to 27% increase for the same SG scenario. This result is robust under our experimental uncertainty and many other assumptions. We outline systematic uncertainties that remain and provide three examples of experiments that might further reduce uncertainties of CaCO
3 SG. Finally, we highlight the importance of the link between experiments and models in studies of SG.
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