In What others are saying

Dirtier air was associated with lower scores in a study of 2,400 students at a central London university as they sat more than 10,000 papers. Separate research on school exams suggested that air quality on the day could have as big an impact on results as class size.

Researchers warned that pollution exposure before “high stakes” tests such as A levels risked serious consequences, as one poor day could cost pupils a university place. Sefi Roth, of the London School of Economics, who carried out both pieces of work, said that parents and pupils should think about air quality on exam days, adding: “They can limit their outdoor activity on polluted days or take less polluted routes when they go to school.”

Although the studies were observational and could not prove that the pollution caused lower marks, they add to a growing body of research suggesting that it blunts cognitive performance and makes people less productive.

The Times for a new Clean Air Act includes a call to cut the legal limits for particulate matter — the most dangerous form of air pollution — by more than half.

The university study analysed how levels of a particulate known as PM10 inside exam halls affected performance. When levels breached World Health Organisation limits, students scored more than two percentage points lower than those in halls below the limit. The WHO limit for PM10 is 50 micrograms per cubic metre. Some exam halls had 75 micrograms, enough to reduce a student’s score by 3.4 percentage points.

High pollution levels were linked to a reduced probability of a student achieving a first-class university degree.

The other study looked at 400,000 exams taken by pupils sitting the Israeli equivalent of A levels.

Taking an exam on a relatively polluted day, when a type of fine particulate matter called PM2.5 was 23.5 micrograms per cubic metre or above, was associated with a 3 per cent decline in a student’s test scores.

The effect was seen even when pollution was within the WHO safety limit of 25 micrograms.

Students who sat exams on high pollution days had a lower chance of obtaining a place at university. Sitting important exams on days with dirty air was also associated with earning less as an adult.

A link between pollution and cognitive performance “would imply that a narrow focus on traditional health outcomes, such as hospitalisation and increased mortality, may understate the true cost of pollution as mental acuity is essential to worker productivity in many professions,” Dr Roth said.

PM10 is particulate matter 10 micrometres or less in diameter, PM2.5 is 2.5 micrometres or less. A human hair is about 100 micrometres across. Sources include car exhausts, pollen and dust.

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