Paul Griffiths, James Keeble, Alex Archibald, Youngdub Matthew Shin, John Pyle, Nathan Luke Abraham

We study the evolution of tropospheric ozone over the period 1979-2010 using a chemistry-climate model employing a stratosphere-troposphere chemistry scheme. By running with specified dynamics, the key feedback of composition on meteorology is constrained, isolating the chemical response. By using historical forcings and emissions representative, interactions between processes are realistically represented. We use the model to ask how the ozone responds over time and to investigate model responses, sensitivities, feedbacks and trends. We find that the CFC-driven decrease in stratospheric ozone plays a significant role in the tropospheric ozone burden. Over the period 1979-1994, the decline in transport of ozone from the stratosphere partially offsets an emissions-driven increase in tropospheric ozone production. From 1994-2010, stratospheric ozone recovery, and a levelling off in emissions, effect a small increase in the tropospheric ozone burden. These results have implications for the impact of future stratospheric ozone recovery on air quality and radiative forcing.