Feb 6, 2018

Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery

by
Ball, William T., Alsing, Justin, Mortlock, Daniel J., Staehelin, Johannes, Haigh, Joanna D., Peter, Thomas, Tummon, Fiona, Stübi, Rene, Stenke, Andrea, Anderson, John, Bourassa, Adam, Davis, Sean M., Degenstein, Doug, et al
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Atmospheric Chemistry and Physics
  • Provides background on ozone formation: states that ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere; states that ozone is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective ozone layer around the globe
  • States that human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses
  • States that total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°)
  • Reports evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has continued to decline since 1998
  • Finds that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N
  • Finds that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases
  • Concludes that the reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established