Millions of Londoners breathed air contaminated with record-breaking levels of a harmful pollutant for which there is no known safe exposure this month, the Standard has learned.
Every air quality monitoring site in the capital hit “high” or “very high” during the smog episode from Thursday March 10 to Sunday March 13.
The minute particles, known as PM2.5, are particularly dangerous because they can penetrate deep into lung tissue and are too small to be filtered out by the body’s normal defences.
The “spike” in smog was caused by dirty air from industrial areas of Germany, Holland and Poland — as well as from fertilisers being sprayed on farmland — drifting towards south-east England on an easterly air flow.
Once it reached London it was trapped by still anti-cyclonic conditions, and made even filthier by the usual daily emissions from London’s vehicles, particularly from diesel engines.
The peak day was the Saturday when 11 out of the 18 measuring sites in London hit “very high” with the rest on “high”.
These were the worst readings since PM2.5 started to be measured in 2012 because of growing concern about its impact on health.
The move followed a report from the Government’s Air Quality Expert Group that found spikes in PM2.5 levels were linked to “increases in hospital admissions and premature death of the old and sick due to diseases of the respiratory and cardiovascular systems”.
Longer-term exposure is associated with lung cancer, and the report concluded “no wholly safe level has been identified”.
Professor Sir Malcolm Green, founder of the British Lung Foundation, has described breathing in high levels of PM2.5 as “like inhaling little particles of tar. They go right down into the lungs and can pass through the membrane into the bloodstream.”
Simon Birkett, founder of the Clean Air in London campaign, said: “It’s a national disgrace that it’s taken an investigation by the Evening Standard to unearth the worst air pollution episode in recent years.
“Worse, Sadiq Khan and Zac Goldsmith both refused to share our tweeted smog warnings at the time.”
Their Green rival mayoral candidate Sian Berry and Lib-Dem Caroline Pidgeon have both committed to introducing smog warnings for London if they are elected in May.