European Space Agency Says 2007 Ozone Hole 'Smaller Than Usual'
The ozone hole over Antarctica has shrunk 30 percent as compared to last year's record size, the European Space Agency (ESA) announced on Oct. 3.
According to measurements made by ESA's Envisat satellite, this year?s ozone loss peaked at 27.7 million tons, compared to the 2006 record ozone loss of 40 million tons. 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 0 degrees Celsius 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 and is not indicative of a long-term trend.
For more information, contact ESA at http://www.esa.int/esaCP/index.html
This article originally appeared in the 10/01/2007 issue of Environmental Protection.