The sensitivity of stratospheric ozone through the 21st century to N2O and CH4
Through the 21st century, anthropogenic emissions of the greenhouse gases N 2 O and CH 4 are projected to increase, thus increasing their atmospheric concentrations. Consequently, reactive nitrogen species produced from N 2 O and reactive hydrogen species produced from CH 4 are expected to play an increasingly important role in determining stratospheric ozone concentrations. Eight chemistry-climate model simulations were performed to assess the sensitivity of stratospheric ozone to different emissions scenarios for N 2 O and CH 4 . Global-mean total column ozone increases through the 21st century in all eight simulations as a result of CO 2 -induced stratospheric cooling and decreasing stratospheric halogen concentrations. Larger N 2 O concentrations were associated with smaller ozone increases, due to reactive nitrogen-mediated ozone destruction. In the simulation with the largest N 2 O increase, global-mean total column ozone increased by 4.3 DU through the 21st century, compared with 10.0 DU in the simulation with the smallest N 2 O increase. In contrast, larger CH 4 concentrations were associated with larger ozone increases; global-mean total column ozone increased by 16.7 DU through the 21st century in the simulation with the largest CH 4 concentrations and by 4.4 DU in the simulation with the lowest CH 4 concentrations. CH 4 leads to ozone loss in the upper and lower stratosphere by increasing the rate of reactive hydrogen-mediated ozone loss cycles, however in the lower stratosphere and troposphere, CH 4 leads to ozone increases due to photochemical smog-type chemistry. In addition to this mechanism, total column ozone increases due to H 2 O-induced cooling of the stratosphere, and slowing of the chlorine-catalyzed ozone loss cycles due to an increased rate of the CH 4 + Cl reaction. Stratospheric column ozone through the 21st century exhibits a near-linear response to changes in N 2 O and CH 4 surface concentrations, which provides a simple parameterization for the ozone response to changes in these gases. © 2012 Author(s).