On the Changing Role of the Stratosphere on the Tropospheric Ozone Budget: 1979-2010

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 suppressed, isolating the chemical response. By using historical forcings and emissions, interactions between processes are realistically represented. We use the model to assess how the ozone responds over time and to investigate model responses and trends. We find that the chlorofluorocarbon (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, despite a leveling off in emissions, increased stratosphere-to-troposphere transport of ozone drives 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.