MONTREAL -- It's been about four months since Montreal schoolchildren began, unintentionally, to take part in what may end up being a huge naturally occurring science experiment: how well air purifiers work.

Since January, most English public schools in the Montreal area have had air purifiers, air exchangers or some other form of extra air-quality device if they don't have built-in mechanical ventilation.

French public schools in the same types of buildings have not had air purifiers.

The provincial government continues to say that air purifiers aren't necessary or proven to work, but the citizen paying the closest attention to the numbers says that based on his data so far, it seems they do.

"I can measure that," Olivier Drouin, who runs the website Covid Ecoles Quebec, told CJAD radio on Friday.

"I can measure that with not just two or three sample data... with 1,000 schools, and with 60 schools plus that have air purifiers," he said.

More specifically, he's found that the schools without air purifying devices have more than three times as many COVID-19 cases as the others, he said.

"The number of cases that [schools with air purifiers] reported, on average, per school versus where there's no... air quality measures... is three to four times fewer cases," he said.

"Air quality measures," for his purposes, include not just air purifiers but air exchangers and a couple of similar devices that serve a similar function, Drouin said.

Drouin also spoke in March to La Presse about these patterns. He told the paper that in a sample of 677 schools with confirmed COVID-19 cases since the beginning of January, he'd found 4,223 cases in total, an average of 6.8 cases per school. But in the 62 schools with purifiers, he only found 110 cases or an average of 1.8 cases per school, about a quarter of the broader rate.

The schools that have air-purifying devices aren't just English public schools. Many private French schools have them as well, he said.

All schools boards that have them bought them at their own expense. The EMSB has spent nearly $2 million to buy and install 800 air purifiers in about 30 schools, after doing its own air-quality survey. The Lester B. Pearson school board spent just over half a million on 420 units. 

Since last August, when Quebec schools opened again in person, Drouin has been keeping a running tally of case counts at various schools on his website, which is popular among Quebec parents.

At first, there was no official count available from the province and Drouin's citizen-run site was the only source of statistics available.

He asks parents to submit official letters about cases at their kids' schools and has his own verification process. He has also been able to check his numbers against the province's statistics since the fall, when a government-provided count became available not long after his website.

Drouin, who is a father of two daughters, said that he's upset by his own findings.

"I am outraged, and I also don't understand that, because many of those measures did not cost hundreds of millions of dollars to implement -- they're actually low-cost measures," he said.

For schools suffering from poor air quality, he called air purifiers "low-hanging fruit" as a solution.


The province hasn't yet been reached for comment on Drouin's findings. But last week, facing increasing criticism over the issue, Education Minister Jean-François Roberge said there's no proof that any outbreak in any Quebec school can be linked to poor air quality.

He and the CAQ government have been questioned especially closely this month on how exactly they're measuring air quality in schools.

A Radio-Canada investigation last week showed problems with the testing system the province is using.

The tests measure carbon dioxide levels as a proxy for determining how fresh the air is. But in three out of five tests, the investigation found, the protocol that was used also changed the results -- it tended to improve the data by reducing the amount of carbon dioxide in the classroom being tested.

Still, even using that method, the tests found that about half of Quebec schools showed high levels of CO2 -- over 1,000 parts per million of carbon dioxide -- and required corrective action according to a provincial threshold, the Journal Métro newspaper reported.

There are about 7,000 classrooms in this group, it said.

Roberge said that while this wasn't ideal, the situation is only truly worrying at over 1,500 parts per million, which applies to only about one in 10 schools.

He also said that the province has now bought 400 air exchangers. The other classrooms in the group of 7,000 are also expected to adjust mechanical ventilation systems or open windows and doors, the Journal Métro reported.

The province has refused to compensate the EMSB and other school boards that supplied their own air purifiers, saying there was no need for them.

Liberal leader Dominique Anglade called for Roberge's resignation over the issue in early April, but Premier François Legault shot back last week by saying the Liberals are "obsessed" with air purifiers and that they don't "respect" health experts.

Listen to Olivier Drouin's interview here: