Ozone layer will thin even as holes heal

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Ozone layer will thin even as holes heal


16:00 06 March 02

NewScientist.com news service

A new study suggests that even as the ozone holes over the poles heal, ozone levels in mid-latitudes, where the majority of the world's population lives, are set to worsen later this century.

And, unlike today, the ozone layer will be at its thinnest in late summer - at the height of the holiday season. The result could be soaring death rates from skin cancers.

Until now, the main cause of the thinning ozone layer and seasonal ozone holes has been a build-up of chlorine and bromine compounds in the stratosphere. Thanks to the 1987 Montreal Protocol, emissions of these compounds are falling fast and the holes should be repaired by mid-century.

Scientists assumed that the ozone layer away from the poles would recover at the same time. But a modelling analysis by the Australian research agency CSIRO casts doubt on this.

Ian Plumb and colleagues calculate that rising emissions of another ozone-destroying chemical, nitrous oxide, will soon put the improvement into reverse in mid-latitudes. "Ozone will recover only partially towards pre-1980 levels, and will then decline," says Plumb.


Hot summer


Nitrogen fertilisers in soils release nitrous oxide when broken down by bacteria. Nitrous oxide is also produced by industrial processes and the burning of fossil fuels. The UN's Intergovernmental Panel on Climate Change predict the gas's concentration in the air will rise 45 per cent by 2100.

Ozone levels in mid-latitudes are currently an average of six per cent less than in 1980. Plumb says they will recover a little, but start falling again after 2040. They could be nine per cent lower by the end of the century, and still falling fast.

Ozone destruction involving chlorine and bromine compounds occurs fastest in spring. This, combined with freezing polar air, caused the ozone holes. But nitrous oxide destroys ozone fastest in summer.

This means it is unlikely to recreate the ozone holes. But it will make the ozone layer over Europe and North America thinnest just when the most ultraviolet radiation is hitting the atmosphere.


Double edged


"The findings sound very interesting," said Stuart Penkett, an atmospheric chemist at the University of East Anglia. "Some of us have warned this was possible. But nobody has sat down and thought things through till now."

Plumb also warns that efforts to control global warming by reducing emissions of the greenhouse gas methane could make matters worse.

This is because the breakdown of methane in the stratosphere creates ozone. So reducing emissions of this gas would be good for the climate, but bad for the ozone layer.

Journal reference: Geophysical Research Letters (DOI: 10.1029/2001GL014295)

http://www.newscientist.com/news/news.jsp?id=ns99992010

azezil

The creation and destruction of ozone molecules in the stratosphere are natural cycles. The average life of an ozone molecule is relatively short in nature, but until recently, ozone was being created at least as quickly as it was destroyed since the oxygen molecule continually rejoins to rejuvenate the ozone layer.

The increase of chlorines and bromines into the atmosphere has interfered with the natural cycle.

Ozone is now being destroyed more quickly than it can be created. When the emissions of these chemicals cease, the ozone layer will eventually repair itself. The repair will not be instantaneous. Even if all CFC emissions were immediately stopped, depletion of the ozone would continue to worsen for 15-20 years before any repair would begin. The natural rejuvenation of the ozone will be a very slow process. Estimates are that the Antarctic ozone hole will not be fully repaired until the late 21st century.

So nature can't do it itself why can't we create our own ozone?

The other difficulty with simply manufacturing ozone is that the sun provides huge amounts of energy for the ozone production process. In fact, to produce the amount of ozone normally in the ozone layer, you'd have to use about double the total annual U.S. electricity production. There's simply no way we could create ozone fast enough, in large enough quantities, to replace the natural ozone production process.

Maybe not now, but if some other source of energy was discovered which does not produce chlorines or bromines maybe would could rebuild our ozone. (azezil forever optimestic )