2020 Arctic Ozone Hole is Largest Ever Observed

The largest recorded ozone layer hole over the Arctic has been detected by the OSIRIS instrument. Normally, holes of this magnitude form only over the South Pole, as the conditions required to form an ozone hole over the North Pole are rare. The last hole to form over the North Pole was in 2011.

A stable polar vortex formed this year over the North Pole, which allowed the ozone-depleting CFCs to reduce the region's ozone layer without being dissipated by the surrounding atmosphere.

Figure 1 shows ten days of OSIRIS measurements over mid-March at various altitudes. The hole is apparent, especially when compared to all of the March 2018 measurements shown in Figure 2, which represent typical values.

Figure 3 shows OSIRIS ozone profiles from different areas around the Pole, some profiles inside the ozone hole region and others outside for comparison.

Figure 1: The 2020 Northern Ozone Hole. Scatterplot of OSIRIS ozone number density measurements from March 10 to March 20. Compared to 2008 (a typical year) the measurements are very low (cf. Figure 2).
Figure 2: A scatterplot of typical March ozone number density over the North Pole. There are more data points as this plots all the data from March 1 to 31.
Figure 3: A selection of ozone profiles measured by OSIRIS inside and outside of the 2020 North Pole ozone hole. The ozone values are very low around 20km where they should be at their peak value.

Unprecedented Forest Fire Aerosol in the Stratosphere

In this study we use satellite measurements, including OSIRIS, that observe the vertical structure of the atmosphere with high sensitivity to thin aerosol layers to report on the long‐lasting stratospheric effect of western North American wildfires from the summer of 2017. Aerosol from these fires was known to reach the stratosphere and circulate throughout the Northern Hemisphere. However, these satellite measurements, which have a record that stretches almost 40 years, show that this fire generated a stratospheric aerosol cloud almost 10 times thicker than background levels and lasted for more than 5 months. This is the largest impact from wildfires ever observed in the 40‐year satellite record.

Figure 9: The difference in aerosol extinction measured during and after the February 2009 Australian bush fire event measured by OSIRIS (relative to January 2009) (left). The same during and after the August 2017 Canadian forest fire event measured by OMPS (relative to July 2017) (right). The black triangles mark the approximate latitude of the fires. Region below the thermal tropopause is shown in gray.

OSIRIS Ozone Contributes to 2018 Scientific Assessment of Ozone Depletion

OSIRIS stratospheric ozone profile measurements from 2002-2018 were used to assess the trends in ozone recovery reported in the 2018 Ozone Assessment. These data helped to conclude that the start of the recovery of stratospheric ozone has begun, and that the continued success of the Montreal Protocol in protecting stratospheric ozone depends on continued compliance.

Figure ES-7: Ozone trends in the stratosphere. The largest relative depletion of ozone outside the polar regions occurred prior to 1997 in the northern mid-latitude, upper stratosphere (left panel). The largest recovery has occurred in the same region, with an upward trend of about 3% per decade since 2000 above 40-km altitude (right panel). Ozone trends derived from satellite observations are shown in brown, with uncertainty ranges given by horizontal lines. Ozone trends derived from a set of chemistry-climate models are shown in orange, with the model variance given by the yellow envelope. Ozone trends from chemistry-climate models agree very well with the measured trends.