Ozone layer turns the corner

Ken Sharpe Considers HCFCs and 25 years of the Ozone hole.

When the realisation that a major ‘hole’ in the ozone layer over Antarctica was occurring in the spring of each year and that ozone levels in the stratosphere were also thinning, I was at the early stages of my involvement with a magazine in the building-services industry. I was therefore able to follow at first hand the concerted international action that led to the signing of the Montreal Protocol in 1987, leading to the banning of HCFC chemicals, many of which were used in air-conditioning and refrigeration systems. One HCFC remains in use — just — and that is R22, but its use for maintenance will no longer be permitted after the end of this year. For information, R22 has an ozone-depletion just a twentieth that of other HCFCs used as refrigerants at the time.

   The problem is that first letter C in HCFC. It represents the chlorine content of that substance. And it is the chlorine that is so destructive of ozone in the stratosphere. The chemistry is complex, but one molecule of chlorine can destroy around a hundred molecules of ozone before it is itself destroyed.

   Now comes the news from the United Nations Environment Programme and the World Meteorological Association that the Earth’s protective ozone layer is well on track to recovery. The news has been a long time coming, over 25 years, but it is testament to the effectiveness of long-term international co-operation. The significance of the news is made more signification that the largest ‘hole’ observed was as recent as 2006. Complete recovery is now expected by around the middle of the century.

   As a slight aside from action to tackle the problem, let us acknowledge the Nobel Prize in chemistry that was awarded to the two scientists who forecast the ozone-depletion problem, F. Sherwood Rowland and Mario Molina.

   In the interim, a whole new generation of refrigerants has been developed, but now we have concerns about their GWP (global-warming potential), which is considerably lower than the ozone-depleting refrigerants they have replaced.

   The impression at this stage is that from the end of this decade there will be restrictions on the GWP of the total content of a system, not the GWP relative to carbon dioxide. So a system can contain a small amount of a substance with a high GWP but more of a substance with a low GWP. Clearly there will be lots more to watch out for in the future.

Ken Sharpe is editor of Modern Building Services

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