Calculations made by combining satellite data with ground-based measurements, including the Antarctica New Zealand Arrival Heights observatory near Scott Base, show that the 2010 Antarctic ozone hole reached a maximum area of approximately 22 million km2 and a maximum ozone mass deficit of approximately 27 million tonnes. In 2009 these figures were 24 million km2 and 35 million tonnes. The largest ozone hole ever recorded was in 2000, when it reached approximately 29 million km2 and 43 million tonnes deficit.
While a one-year reduction in the ozone hole can't, in itself, indicate a recovery stage, NIWA's atmospheric experts, based at Lauder, say the new information adds to a pattern of less severe ozone holes in recent years.
NIWA atmospheric scientist Dr Stephen Wood says the results are encouraging and indicate that international initiatives, such as the Montreal Protocol, may now be showing a positive effect on the Antarctic ozone hole.
The 1987 Montreal Protocol is an international convention phasing out the use of ozone-depleting substances such as chlorofluorocarbons (CFCs) and other manmade halogen compounds.
"We see a lot of year-to-year variation in ozone holes, caused by differences in atmospheric temperature and circulation. So we can't definitively say the ozone hole is improving from one new year of observations. However, we have now had a few years in succession with less severe holes. That is an indication we may be beginning to see a recovery."
"With continued monitoring, and by using the tools we have developed to calculate overall ozone hole severity and statistical analysis of their significance, we will soon be able to assess whether we are really seeing the start of a sustained, long-term recovery," Dr Wood says.
In addition to the Antarctic measurements, NIWA scientists are using sophisticated models on NIWA's new supercomputer to estimate when ozone will recover to the levels they were prior to widespread use of CFCs.
NIWA scientists have been measuring surface ozone at the Arrival Heights laboratory near Scott Base since 1988. Measurements are taken using a Dobson spectrophotometer, an instrument designed in the early 20th century.
Measurements are recorded in Dobson Units (DU). Measurements taken at Arrival Heights this year show the ozone values are still falling below 200 Dobson Units in springtime. Levels this low were not observed in Antarctica before the ozone hole first formed nearly 30 years ago.
The Antarctic ozone hole forms in August and September each year, and remains until it is breaks up in November or December. The summer period is when its effects on Southern mid-latitudes, including New Zealand, are likely to be largest.
Last week NIWA CEO John Morgan visited the Antarctica New Zealand facilities, including the Arrival Heights observatory, as part of the Antarctica New Zealand Invited Visitor programme.
The NIWA measurements of ozone in Antarctica are part of a FRST-funded research programme targeted at understanding what drives global change in the atmosphere. The ground-based measurements are important for validating the measurements made by satellite-based instruments.