Antarctic ozone hole ranks seventh largest in 48 years
The Antarctic ozone hole placed seventh in the area rankings across a 48-year monitoring history, NASA and NOAA reported. An unusually strong polar vortex widened the cold region where ozone destruction occurs. The seasonal assessment also found less severe depletion than in some earlier large holes, alongside continuing long-term recovery under controls on ozone-damaging chemicals.
Science··Morning
A large seasonal hole
NASA and NOAA (the US National Oceanic and Atmospheric Administration) reported on 4 November that the Antarctic ozone hole placed seventh in the area rankings across a 48-year monitoring history. Between 7 September and 13 October, the period of peak depletion, the hole covered an average of about 25 million square kilometres. The daily maximum occurred on 18 September, when its area was 27.1 million square kilometres. Scientists define the hole as the region where the total ozone amount falls below 220 Dobson units, a standard measure of atmospheric ozone.[1]
A strong vortex widened the cold region
The Antarctic polar vortex maintains cold conditions in which chlorine and bromine from human-made compounds destroy stratospheric ozone. NOAA researcher Amy Butler said atmospheric waves that normally disrupt the vortex were unusually weak in August and September. Strong vortex winds consequently remained farther from the pole, widening the cold area favorable to ozone loss. Balloon instruments above the South Pole measured the year’s lowest ozone amount there at 105 Dobson units on 17 October. The historical minimum at that location was 92 units in October 2006.[1]
Chemical controls support long-term recovery
The agencies said the protective ozone layer remains on a path toward long-term recovery under controls established by the 1987 Montreal Protocol. Chemicals once widely used in refrigerators, air conditioners and insulation can persist for decades in the atmosphere and old products. This year’s assessment combines balloon and ground observations with measurements from Aura, a NASA satellite; the NOAA-20 and NOAA-21 satellites; and Suomi National Polar-orbiting Partnership, operated jointly by the two agencies. Despite the large area, depletion was less deep than in some earlier large holes. Stratospheric ozone shields life from harmful solar radiation. The atmospheric layer’s protective role differs from that of ozone near the ground, where the gas is an air pollutant.[1]
