The impact of greenhouse gases on past changes in tropospheric ozone

Abstract

The impact of changes in the abundance of greenhouse gases (GHGs) on the evolution of tropospheric ozone (O 3) between 1960 and 2005 is examined using a version of the Goddard Earth Observing System chemistry-climate model (GEOS CCM) with a combined troposphere-stratosphere chemical mechanism. Simulations are performed to isolate the relative role of increases in methane (CH 4) and stratospheric ozone depleting substances (ODSs) on tropospheric O 3. The 1960 to 2005 increases in GHGs (CO 2, N 2 O, CH 4, and ODSs) cause increases of around 1-8% in zonal-mean tropospheric O 3 in the tropics and northern extratropics, but decreases of 2-4% in most of the southern extratropics. These O 3 changes are due primarily to increases in CH 4 and ODSs, which cause changes of comparable magnitude but opposite sign. The CH 4 -related increases in O 3 are similar in each hemisphere (∼6%), but the ODS-related decreases in the southern extratropics are much larger than in northern extratropics (10% compared to 2%). This results in an interhemispheric difference in the sign of past O 3 change. Increases in the other GHGs (CO 2 and N 2 O) and SSTs have only a small impact on the total burden over this period, but do cause zonal variations in the sign of changes in tropical O 3 that are coupled to changes in vertical velocities and water vapor. © 2012. American Geophysical Union. All Rights Reserved.