Modern Aspects of Understanding Stratospheric and Tropospheric Ozone
Dr Andrea Stenke
ETH Zurich, Institute for Atmospheric and Climate Science, Switzerland
Time & Place
Fri, 25 Jan 2019 11:00:00 NZDT in West 701, Level 7
All are welcome
Ozone forms in the atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the so-called Brewer-Dobson circulation (BDC), forming a protective layer around the globe, which shields the Earth’s surface from harmful UV radiation. Human emissions of halogen-containing ozone-depleting substances led to a decline in stratospheric ozone until they were banned by the Montreal Protocol. The success of the Montreal Protocol is clearly visible in the upper stratosphere, where since 1998 ozone is rising again. In contrast, there is evidence from multiple satellite measurements that ozone in the lower stratosphere between 60°S and 60°N has indeed continued to decline since 1998. So far, the reasons for this continued ozone reduction are not clear. While climate models are capable of reproducing the upper stratospheric recovery, they do not reproduce the trends in the lower stratosphere, and thus the causes now urgently need to be established.
Since tropospheric ozone is both a greenhouse gas and harmful air pollutant, clean air laws and regulations intended to decrease tropospheric ozone levels. However, satellite measurements indicate a continuous increase in tropospheric ozone, and climate models even project elevated ozone levels until the middle of the 21st century, at least for northern mid-latitudes. Overall, the positive ozone trends in the upper stratosphere and in the troposphere balance the downward trend in the lower stratosphere, which causes the total ozone column to be approximately constant.