Modeled and Observed Volcanic Aerosol Control on Stratospheric NO_y and Cl_y

Decreases in stratospheric NO_x associated with enhanced aerosol have been observed after large volcanic eruptions, for example, after the eruption of Mount Pinatubo in 1991. While the 1991 Mount Pinatubo eruption was the last large explosive eruption, recent studies have shed light on the impacts of moderate-sized eruptions since the year 2000 on the global stratospheric aerosol budget. We use an ensemble of simulations from a coupled climate-chemistry model to quantify and analyze changes in NO and NO₂ (NO_x), N₂O₅, HNO₃, ClO, and ClONO₂ during periods of increased stratospheric volcanic aerosol concentrations since 2000. By using an ensemble approach, we are able to distinguish forced responses from internal variability. We also compare the model ensemble results to satellite measurements of these changes in atmospheric composition, including measurements from the Optical Spectrograph and Infrared Imaging Spectrometer on the Odin satellite and the Aura Microwave Limb Sounder. We find decreases in stratospheric NO_x concentrations up to 20 hPa, consistent with increases in stratospheric HNO₃ concentrations. The HNO₃ perturbations also extend higher, up to 5 hPa, associated with periods of increased volcanic aerosol concentrations in both model simulations and observations, though correlations with volcanic aerosol are considerably higher in the model simulations. The model simulates increases in ClO at altitudes and magnitudes similar to the NO_x reductions, but this response is below the detectable limit in the available observations (100 pptv). We also demonstrate the value of accounting for transport-related anomalies of atmospheric trace gases by regression onto N₂O anomalies.