Chemicals, cold led to 2011 Arctic ozone hole: new NASA study

The left image shows March 19, 2010 ozone concentrations in the Arctic and the right shows the same date in 2011. March 2010 had relatively high ozone, while March 2011 has low levels. (IMAGE COURTESY OF NASA)

A combination of extreme cold temperatures, man-made chemicals and a stagnant atmosphere were behind what became known as the Arctic ozone hole of 2011, a new NASA study finds.

Generally, the ozone layer, which wraps around the planet like a blanket about 20 kilometres above the surface, filters out damaging ultraviolet rays from the sun.

But, in 2011, a hole in that ozone layer covered two million square kilometres and allowed high levels of harmful ultraviolet radiation to hit large swaths of northern Canada, Europe and Russia.

Even when both poles of the planet undergo ozone losses during the winter, generally the Arctic’s ozone depletion tends to be milder and shorter-lived than the Antarctic’s, NASA reported March 11.

That’s because the three key ingredients needed for ozone-destroying chemical reactions — chlorine from man-made coolants called, chlorofluorocarbons, frigid temperatures, and sunlight — are not usually present in the Arctic at the same time.

And the northernmost latitudes of the Arctic are generally not cold enough when the sun reappears in the sky in early spring.

But in 2011, ozone concentrations in the Arctic atmosphere were about 20 percent lower than its late winter average.

The new study shows that, while chlorine in the Arctic atmosphere caused severe ozone loss of winter of 2011, unusually cold and persistent temperatures also spurred on the ozone destruction.

“You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn’t seen any time where it was this cold for this long,” said Susan E. Strahan, an atmospheric scientist with NASA, and main author of the new paper, which was recently published in the Journal of Geophysical Research-Atmospheres.

“Arctic ozone levels were possibly the lowest ever recorded, but they were still significantly higher than the Antarctic’s,” she said.