Volcanic Perturbations of Stratospheric Ozone in Contemporary and Future Atmospheres
Klobas, J. Eric
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AbstractVolcanic eruption columns possess the potential to transport great quantities of reactive gases to the stratosphere where they might subsequently interact with ozone. While explosive volcanic eruptions currently increase rates of ozone-loss catalysis due to an enhancement in the availability of reactive chlorine following the stratospheric injection of sulfur, future eruptions are expected to enhance total column ozone as halogen loading approaches pre-industrial levels.
In this thesis, the sensitivity of the ozone layer to future Pinatubo-like volcanic eruptions is explored in the context of the Representative Concentration Pathway (RCP) greenhouse gas emission trajectories. Heterogeneous chemical effects following large eruptions are evaluated in a variety of future atmospheres spanning contemporary times to the year 2100. Differences between the models become evident following an analysis of vertical profile response and total column response. Sensitivity studies are performed to evaluate the effect of stratospheric temperature, methane burden, and hemispheric mass loading.
A predictive random forest regression model is developed and employed to account for the difference between prescribed RCP and World Meteorological Organization (WMO) halocarbon decay rates. While the ozone layer is found to be more sensitive to volcanic perturbation under WMO halocarbon trajectories, the difference between WMO and RCP scenarios is not extreme and does not represent a modal shift in behavior for any of the RCP storylines.
Heterogeneous chemical processing is found to produce net ozone depletions until the 2070's for all RCP scenarios, and significant depletions of greater than 1% ozone loss until the 2060's. These dates occur later than prior estimates due to the inclusion of 4 pptv bromine from short-lived bromocarbons in the chemical model. Using the WMO EESC correction, slight ozone losses are observed following eruptions until the end of the century, though in some cases these losses are smaller than expected ozone contributions from radiative-dynamical causes.
Additionally, tremendous quantities of volcanic halogens are occasionally transported to the stratosphere in the eruption column of a large, explosive volcanic eruption. Volcanic co-injections of sulfur dioxide and hydrogen chloride are evaluated for simulated Pinatubo-scale eruptions with HCl:SO2 molar ratios corresponding to recent MLS results and the ice core record. Halogen-rich eruptions produce global ozone depletion regardless of the halogen background from long-lived anthropogenic halocarbons. In cases of more severe halogen partitioning, 9-year global average losses exceed 8% with more extreme zonal losses predicted over a shorter time horizon. Additionally, it is demonstrated that perturbations of stratospheric ozone by halogen-rich eruptions have significantly longer lifetimes than perturbations of ozone by Pinatubo-like eruptions due to differential decay trajectories of volcanic SO2 and HCl. The stratospheric ozone response to co-injections of HCl with SO2 is shown to scale non-linearly in comparison to individual injections of each component.
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