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When a latter-day smog enveloped London in 1991 the number of deaths
shot up by 10 per cent, according to an unpublished report for the Department
of Health. The figures suggest that the smog killed about 160 people. The
episode presents the first direct evidence of deaths from air pollution
in Britain for more than 30 years and has forced the government to order
a review of its air quality guidelines.

The smog, which built up from traffic fumes during four windless days
in December 1991, was the worst in Britain in recent years. Many of those
who died had probably been suffering from heart disease and respiratory
problems.

Evidence of the deaths has been compiled by Ross Anderson, an epidemiologist
at St George’s Hospital in south London. He will present a summary of his
results to a meeting of the British Thoracic Society next week.

But Anderson’s results have already convinced the Department of Health
to act. Under air quality guidelines which it set last year, no public warning
would be given if the 1991 smog was repeated today, because the level of
pollutants would not be high enough.

The smog blanketed London from the morning of Thursday 12 December
until winds cleared the air the following Sunday evening. Two pollutants
reached exceptionally high concentrations: nitrogen dioxide levels peaked
at 423 parts per billion, the highest level ever recorded in Britain, and
particulates, measured as the amount of black smoke in the air, reached
228 micrograms per cubic metre.

By looking at the number of people in London who died the week before
the smog, and the number who died in the same week in previous years, Anderson
calculated the expected number of deaths for the seven days starting on
12 December. He then compared this figure with the number of people who
actually died.

Anderson found that 10 per cent more people than expected died during
the smog. He declines to say how many deaths make up the 10 per cent or
to comment on his findings until next week’s meeting.

But government figures show that about 1700 people were registered dead
during the fateful week, suggesting that about 160 extra people died during
the smog.

Anderson found the number of people who died from respiratory diseases,
including asthma and severe lung disease, was 22 per cent higher than expected
during the week of the smog. The number of people who died from cardiovascular
disease was 14 per cent higher.

An epidemiological study such as Anderson’s cannot prove that air pollution
caused the extra deaths. But the abstract of Anderson’s paper concludes:
‘The results suggest an increase in mortality occurred during the episode
week. This is consistent with an effect of air pollution.’

Stephen Holgate, professor of immunopharmacology at the University of
Southampton, says it is difficult to be sure that the effect Anderson found
was not caused by weather or another unexpected factor. But the findings
do point to pollution. ‘It is an important result. It reflects the findings
coming out of other countries,’ he says.

It is not clear whether nitrogen dioxide or particulates were to blame.
The nitrogen dioxide levels were more extreme. But a report on the pollutant
last year by the government’s Advisory Group on the Medical Aspects of
Air Pollution Episodes found evidence of only weak effects on breathing
at concentrations up to 600 ppb.

There is growing concern about particulates: Joel Schwartz, an epidemiologist
from Harvard University, calculated that they kill 10 000 people a year
in England and Wales (‘Dying from too much dust’, New Å®ÉúСÊÓƵ, 12 March).
Douglas Dockery, another epidemiologist at Harvard, says Anderson’s results
fit the pattern he has seen in other cities. ‘It is just what we would have
expected from the particulate concentrations,’ says Dockery.

According to John Bower of the National Environmental Technology Centre
near Culham, Oxfordshire, episodes as bad as the 1991 smog are rare. But
they remain possible, despite new regulations intended to reduce vehicle
emissions. ‘If the same weather happens again, it would happen again,’ he
says.

Last year, the Department of Health’s advisory group set a limit of
600 ppb for nitrogen dioxide before the government issued a public health
warning. At the department’s request, the advisory group is meeting this
week to review the limit.