Doubled CO₂ effects on NOy in a coupled 2D model

Stratospheric NO y fields calculated using a zonally averaged interactive chemistry‐radiation‐dynamics model show significant sensitivity to the model CO 2 . Modeled upper stratospheric NO y decreases by about 15% in response to CO 2 doubling, mainly due to the temperature decrease calculated to result from increased CO 2 cooling. The abundance of atomic nitrogen, N, increases because the rate of the strongly temperature dependent reaction N + O 2 → NO + O decreases at lower temperatures. Increased N leads to an increase in the loss of NO y which is controlled by the reaction N + NO → N 2 + O. The decrease in NO y due to the lowered temperatures is partially compensated by changes in the residual circulation. In addition, the NO y reduction is shown to be sensitive to the NO photolysis rate.