SCIENCE How we got clean air

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POI RACTST ICKS THE LONDON smogs I remember from my childhood don't seem to happen these days. Those smogs, mixtures of smoke and fog, were quite exciting to me, but to many they were lethal.

In the great London mog of 1952, some 4000 people, young and old, died.

This was because the tiny droplets of water in the fog trapped the dust and gases of air pollution near ground level, forcing people to breathe more pollution than normal.

Taller factory chimneys helped get rid of some of this air pollution, delivering it to the faster moving layers of air, higher up. So the pollution was carried away to Scotland and Scandinavia to fall as 'acid rain' But the major factor in abolishing smogs was the 1956 Clean Air Act, which allowed local authorities to declare 'smokeless zones'. Thus the open coal fire; cheery but only 2% efficient, was ushered out and people turned to smokeless fuels such as coke and more efficient grates and stoves.

So it was very interesting to look at the history of government policy on clean air as revealed in Cabinet papers released under the 30 year rule.

In December 1952, smog descended on London and in the worst week, the death rate was nearly triple that of the same week in the previots year. The new Tory government set up a committee under Sir Hugh Beaver to investigate the disaster and make recommendations. Nearly a year later the Cabinet met to discuss the Beaver report and a memorandum from Harold Macmillan, minister of housing and local government.

'Supermac' observed that: •Today everybody expects the government to solve every problem. It is a symptom of the Welfare State...

"For some reason, 'smog' has captured the imagination of the press and the people... We canand ventilation in the bedroom.

Now, some amateur research by a New Zealand horticulturalist, Jim Tyler, suggests that a further factor could help determine whether a child at risk of cot death actually dies.

Tyler observed that urea in a sleeping baby's nappy is broken down by bacteria in the baby's faeces, if present in the same nappy, to form the pungent and poisonous gas ammonia. And during an average sleep quite a lot of ammonia can be produced.

Ammonia has a wide range of dangerous effects including the following:

• Small doses irritate the tissues, causing an awake child to cry;

• Larger doses cause swelling of the lung tissues (making breathing more difficult).

Mice given ammonia exper¡ence muscle contraction, rapid breathing and gasping. Continued exposure leads to coma, convulsions and death.

So far, Tyler's theory seems plausible, but is there any evidence to support it?

The strongest evidence is that the amount of ammonia produced in a nappy can be linked with the baby's diet. When babies are switched from breast to bottle milk, they excrete large amounts of urea.

The change in diet also ' stomachs. This means more bacteria in the faeces and more urea to be decomposed to ammonia.

As further support to the theory, most cot deaths occur between three weeks and one year, when the changeover in diet is likely to occur.

According to an expert in cot deaths, Tyler's theory is an interesting one which would be easy to prove or disprove. Strangely, though, his findings have been rejected by medical journals, and he has been forced to publish them himself.

[Information for both articles from 'New Scientist'].

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