Impact of stratospheric changes on past and future tropospheric ozone

A new version of the Goddard Earth Observing System chemistry-climate model (GEOS CCM) with a combined troposphere-stratospheric chemical mechanism is used to examine the impact of stratospheric changes on the evolution of tropospheric ozone. Time-slice integrations were performed for 1960, 2005 and 2100. These simulations differ in values of prescribed ozone depleting substances (ODSs), greenhouse gases (GHGs) and sea-surface temperatures (SSTs). The past decline and projected future recovery in stratospheric ozone lead that the influx of stratospheric ozone into the troposphere decreased between 1960 and 2005 and increases between 2005 and 2100. An increase in mass transport into the troposphere, due primarily to increases in GHGs and SSTs, further enhances the stratospheric contribution in the future. The net stratospheric impact in the past is the largest in the southern extratropics (10-15% decrease in tropospheric burden and surface ozone, compared to 1-3% decrease in northern hemisphere). However, for the scenario considered, the impact in the future is similar in both hemispheres (~10-15% increase in tropospheric burden).