Ozone Hole Getting Smaller
The ozone hole over Antarctica has shrunk 30 percent as compared to last year's record size. According to measurements made by ESA’s Envisat satellite, this year’s ozone loss peaked at 27.7 million tonnes, compared to the 2006 record ozone loss of 40 million tonnes.
Ozone loss is derived by measuring the area and the depth of the ozone hole. The area of this year’s ozone hole - where the ozone measures less than 220 Dobson Units - is 24.7 million sq km, roughly the size of North America, and the minimum value of the ozone layer is around 120 Dobson Units.
A Dobson Unit is a unit of measurement that describes the thickness of the ozone layer in a column directly above the location being measured. For instance, if an ozone column of 300 Dobson Units is compressed to 0º C and 1 atmosphere (the pressure at the Earth’s surface) and spread out evenly over the area, it would form a slab of ozone approximately 3mm thick.
Scientists say this year’s smaller hole - a thinning in the ozone layer over the South Pole - is due to natural variations in temperature and atmospheric dynamics (illustrated in the time series to the right) and is not indicative of a long-term trend.
"Although the hole is somewhat smaller than usual, we cannot conclude from this that the ozone layer is recovering already,” Ronald van der A, a senior project scientist at Royal Dutch Meteorological Institute (KNMI), said.
"This year's ozone hole was less centred on the South Pole as in other years, which allowed it to mix with warmer air, reducing the growth of the hole because ozone is depleted at temperatures less than -78 degrees Celsius."
Source: ESA Portal