NIWA's Richard Querel talks about the ozone hole, including this year's large one, and Ben Liley explains why NZ has such high UV levels.

The 2020 Antarctic ozone hole is one of the largest and deepest of recent years, due to stratospheric weather conditions trapping cold air high above the frozen continent.

This year also saw the first significant ozone hole appear over the Arctic.

But overall, scientists say the ozone layer remains on a path to recovery.

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The thinning of the ozone layer over Antarctica each southern spring was first detected from the ground in the early 1980s.

The first measurements that showed ozone depletion were made using a Dobson ozone photospectrometer, a machine developed in 1924.

About 120 were built and about 50 are still in use around the world today. There is a Dobsonmeter at Arrival Heights near New Zealand's Scott Base and another at NIWA's Lauder Research Station in Central Otago.

In 1983, the first satellite image of the ozone hole as seen from space was made, and the discovery of the ozone hole was published in 1985.

Scientists think of ozone as a column extending from the earth's surface to the top of the atmosphere. It is measured in Dobson Units.

Average global levels of ozone are about 300 Dobson Units, and an ozone hole is defined as an extended period where ozone is less than 220 Dobson Units.

Ozone levels over Antarctica shrunk to a record low of 89 Dobson Units in 2006.

The annual ozone hole varies in size considerably from year-to-year, depending on regional weather conditions in the stratosphere. Extreme cold creates the right chemical conditions for increased ozone destruction.

The 2020 ozone hole is one of the largest and deepest of recent years.

On 6 October this year, ozone levels got down to 94 Dobson Units,

NOAA and NASA report that at its peak on the 20 September the hole covered an area of 24.8 million square kilometres, the size of North America. There was virtually no ozone in a 6.4-kilometre-high column of the stratosphere over the South Pole.

However, in terms of ozone holes over the past four decades, this year's persistent ozone hole - which started forming in mid-August and is still going strong in late November - is only the 12th largest on record.

https://youtu.be/2tpvU46-CFs

This year's large hole is in contrast to last year's, which was the smallest on record, covering a mere 16.4 million square kilometres…

Go to this episode on rnz.co.nz for more details