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THE mystery of why some thunderstorms trigger massive asthma outbreaks has
been cracked by researchers in Australia. They say intense downdraughts of cold
air that sweep up pollen and dust are to blame.

Their work also suggests the problem is greater than anyone realised. But if
forecasters could predict storms of the type likely to trigger attacks, it would
be possible to give sufferers advance warning.

After storms, local hospital emergency departments are sometimes flooded with
people suffering from asthma attacks. Until now it hasn鈥檛 been clear why. It is
at least partly due to moisture making pollen grains rupture and release
allergenic particles. But this doesn鈥檛 explain why only some storms trigger
epidemics, rather than any rainy day.

In Wagga Wagga, New South Wales, on 30 October 1997, over 200 people with
asthma attended the local hospital after a thunderstorm. When Guy Marks of the
University of Sydney and his colleagues investigated, they realised that the
鈥渙utflow鈥� from the thunderstorm could be to blame. This low layer of cold air
spreads outwards from the intense downdraughts beneath some storms. Weather
records showed that a dramatic rise in the pollen count was associated with the
outflow.

To test the theory, the researchers looked at asthma epidemics and the
corresponding weather records in six towns in south-eastern Australia, including
Wagga Wagga. They found that 33 per cent of outbreaks happened after
thunderstorms with outflows, whereas only 15 per cent occurred after
thunderstorms with no outflows.

During late spring and summer, when pollen counts are higher, the connection
was even stronger, with epidemics following half of all thunderstorms with
outflows. 鈥淲e believe these findings offer an explanation for the mechanism of
thunderstorm-related epidemics of asthma,鈥� says Marks. 鈥淔urthermore, our study
shows that these events may be more common than previously appreciated.鈥�