School attendance increased by 1.3 days per pupil per year when five elementary schools in Milan, Italy, introduced air filters into classrooms, in the first randomised controlled trial of its kind.
鈥淚t鈥檚 the first experimental evidence,鈥� says at the Polytechnic University of Milan. Her team installed high-quality portable air purifiers in 43 randomly chosen classrooms in the schools. Renna describes these as being better than filters.
The researchers recorded an increase in attendance of 1.3 days per pupil per year in the classrooms with air filters, which corresponded with a 12.5 per cent fall in absenteeism. 鈥淚t鈥檚 a pretty large effect,鈥� says Renna, who presented at a meeting of the European Geosciences Union in Vienna, Austria, this week.
Advertisement
They also found that there was a 32 per cent reduction in PM2.5 particulate matter in these classrooms, but Renna can鈥檛 say for sure whether the fall in absenteeism is due to the reduction in air pollution, lower levels of pollen or pathogens such as viruses, or perhaps some combination of these factors.
A trial in 10 schools in the UK in 2021 and 2022 found that HEPA filters reduced sick days due to covid-19 by 20 per cent, for instance. But Renna鈥檚 team did find the effect was weaker when air pollution was especially high, which she thinks is because the air filters can鈥檛 keep up in such conditions.
Because the trial wasn鈥檛 blinded by, say, the control group consisting of classrooms that were also given air purifiers but with the filters removed, the researchers can鈥檛 rule out a psychological contribution to the findings, either. Larger randomised trials of air purifiers in schools are under way elsewhere, says Renna.
Milan has a particular problem because air pollution can be trapped by mountains around the city, she says. 鈥淰ery few other places in Europe are as bad.鈥� However, many other European cities do breach World Health Organization guidelines for air pollution, says Renna.
