The changing ozone depletion potential of N2O in a future climate Laura Revell1,2, Fiona Tummon2, Ross Salawitch3, Andrea Stenke2, and Thomas Peter2 1Bodeker Scientific, New Zealand, laura@bodekerscientific.com 2Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland 3Department of Atmospheric and Oceanic Sciences, University of Maryland, US Revell et al., GRL, 2015, doi:10.1002/2015GL065702

Increasing CO2 and CH4 lead to less N2O-induced ozone destruction x x x Rate of NOx-induced ozone loss (10-14 molecules s-1) CH4 (ppb) x x x Results from the SOCOL chemistry- climate model: 9 year 2100 time-slice simulations based on RCP 6.0 x x x CO2 (ppm)

Increasing CO2 and CH4 lead to less N2O-induced ozone destruction x x x Rate of NOx-induced ozone loss (10-14 molecules s-1) CH4 (ppb) x x x x x x More CH4: OH + NO2 + M → HNO3 + M CO2 (ppm)

The ODP of N2O is sensitive to CO2 and CH4 concentrations 8.5 CH4 (ppb) Year 2100 ODPN2O 6.0 4.5 2.6 CO2 (ppm)

The ODP of N2O is sensitive to CO2 and CH4 concentrations 8.5 Year 2000 ODPN2O 0.015 SOCOL 0.017 Ravishankara et al., 2009 0.019 Daniel et al., 2010; Fleming et al., 2011 CH4 (ppb) Year 2100 ODPN2O 6.0 4.5 2.6 CO2 (ppm)

The ODP of N2O is sensitive to CO2 and CH4 concentrations 8.5 Year 2000 ODPN2O 0.015 SOCOL 0.017 Ravishankara et al., 2009 0.019 Daniel et al., 2010; Fleming et al., 2011 CH4 (ppb) Year 2100 ODPN2O Year 2100 ODPN2O RCP 2.6 0.024 RCP 4.5 0.022 RCP 6.0 0.019 RCP 8.5 0.016 6.0 4.5 2.6 CO2 (ppm)

The ODP of N2O is sensitive to CO2 and CH4 concentrations 8.5 Year 2000 ODPN2O 0.015 SOCOL 0.017 Ravishankara et al., 2009 0.019 Daniel et al., 2010; Fleming et al., 2011 ??? CH4 (ppb) Year 2100 ODPN2O Year 2100 ODPN2O RCP 2.6 0.024 RCP 4.5 0.022 RCP 6.0 0.019 RCP 8.5 0.016 6.0 4.5 2.6 CO2 (ppm)

The resulting change in global-mean total ODPs for N2O quantify ozone loss due to N2O, relative to ozone loss due to CFC-11 ODP N2O = m CFC11 × τ N2O × ∆ μ CFC11 ×[∆ O 3 ] N2O m N2O × τ CFC11 × ∆ μ N2O ×[∆ O 3 ] CFC11 Molecular mass Atmospheric lifetime Prescribed change in the surface mixing ratio The resulting change in global-mean total column ozone

The resulting change in global-mean total ODPs for N2O quantify ozone loss due to N2O, relative to ozone loss due to CFC-11 ODP N2O = m CFC11 × τ N2O × ∆ μ CFC11 ×[∆ O 3 ] N2O m N2O × τ CFC11 × ∆ μ N2O ×[∆ O 3 ] CFC11 Molecular mass Atmospheric lifetime Prescribed change in the surface mixing ratio The resulting change in global-mean total column ozone

Rate of chlorine-induced ozone loss Chlorine-induced ozone destruction slows with increasing CH4 and decreasing CO2 CH4 (ppb) Rate of chlorine-induced ozone loss (10-14 molecules s-1) More CH4: CH4 + Cl → CH3 + HCl CO2 (ppm)

Difference in rate of chlorine-induced ozone loss due to CO2 (%) The effect of CO2 on chlorine-induced ozone destruction varies with location Pressure (hPa) Difference in rate of chlorine-induced ozone loss due to CO2 (%) Latitude (°)

Uncertainties in atmospheric composition lead to ODPs for N2O differing by up to a factor of two CH4 (ppb) Year 2100 ODPN2O CO2 (ppm)

To conclude: N2O-induced ozone loss N2O-induced ozone destruction slows with larger CO2 and CH4 concentrations. CH4 CO2

To conclude: N2O-induced ozone loss N2O-induced ozone destruction slows with larger CO2 and CH4 concentrations. CH4 CFC-11-induced ozone loss CO2 CFC-11-induced ozone loss slows with larger CH4 and smaller CO2 concentrations. CH4 CO2

To conclude: N2O-induced ozone loss N2O-induced ozone destruction slows with larger CO2 and CH4 concentrations. CH4 CFC-11-induced ozone loss CO2 CFC-11-induced ozone loss slows with larger CH4 and smaller CO2 concentrations. CH4 ODPN2O CO2 CH4 Uncertainties in atmospheric composition lead to a wide spread of values for the ODP of N2O. CO2