The ozone hole above the Antarctic was the second smallest seasonal hole in the last 20 years and reached its maximum size for the year on Sept 22.

According to satellite measurements by NASA and National Oceanic and Atmospheric Administration (NOAA) satellites, the size of the Sept. 22 hole was 8.2 million square miles or roughly the size of United States, Canada and Mexico combined.

The average size of the seasonal ozone hole for the year was 6.9 million square miles. Till date, the largest ozone hole recorded was in 2000, covering an area of 11.5 million square miles.

"It happened to be a bit warmer this year high in the atmosphere above Antarctica, and that meant we didn't see quite as much ozone depletion as we saw last year," Jim Butler, the director of global monitoring at NOAA's Earth System Research Laboratory in Boulder, Colorado, said in the statement.

Ozone layer forms a protective layer in the Earth's atmosphere and prevents the harmful effects of ultraviolet rays on humans. Radiation from UV rays can cause skin cancer, and damage plants and aquatic ecosystems.

Ozone molecules can be found in the troposphere (lowest layer of the atmosphere which is closest to the Earth's surface) and in the stratosphere (uppermost layer of the atmosphere).

While ozone on the Earth's surface acts as a pollutant, the stratospheric ozone reflects the UV rays back into space and protects us from its radiation.

The Antarctic ozone hole started making its appearance in the early 1980s. According to scientists, the hole is caused by chlorine released by man-made chemicals called chlorofluorocarbons or CFCs. Chlorine is believed to loiter in the stratosphere for decades. Temperature in the lower stratosphere can affect the rate at which chlorine breaks apart the ozone molecules.

"The ozone hole mainly is caused by chlorine from human-produced chemicals, and these chlorine levels are still sizable in the Antarctic stratosphere," NASA atmospheric scientist Paul Newman, said in a statement.

"Natural fluctuations in weather patterns resulted in warmer stratospheric temperatures this year. These temperatures led to a smaller ozone hole," he said.

Despite an international agreement that was signed 25 years ago to control production of ozone-depleting chemicals, the ozone hole continues to form every year. Newman has predicted that the ozone layer will not recover and return to its early 1980s state until about 2065.