quebec using co2 monitors to gauge air quality in classrooms
a gazette investigation shows readings in everyday settings that rarely surpassed levels recorded in schools, where the quebec government sets an upper threshold of 1,500 ppm.
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with back-to-school around the corner, the quebec government is again facing questions over whether it’s done enough to improve air quality in classrooms.
in recent weeks, quebec education minister jean-françois roberge has insisted schools are now safer than they’ve ever been during the pandemic.
one of the improvements roberge has pointed to is the province adding 90,000 carbon dioxide (co2) monitors to classrooms across the network.
the devices do not improve air quality but can be used to gauge whether a room is well or poorly ventilated. since covid-19 can spread through the air, they’ve also been used as covid risk assessment tools.
“if co2 is increasing in a room, it means you’re not evacuating one of the contaminants accumulating, so that’s probably the case with the others,” explained stéphane bilodeau, an indoor ventilation expert and lecturer in the bioengineering department at mcgill university.
“and if it’s a virus that spreads through aerosols, it will accumulate like co2.”
generally, it is recommended to aim for an indoor rating of under 1,000 parts per million when monitoring c02 levels. the u.s. centers for disease control and prevention has said 800 ppm is a better benchmark during the pandemic.
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the quebec education department, for its part, says that its “target” is for all classrooms to have a daily average concentration of less than 1,000 ppm, but it considers a weekly average of under 1,500 ppm a sign of “satisfactory air quality” – a benchmark experts have argued is much too high.
with that in mind — and as more people will head indoors once the fall approaches — the montreal gazette visited several everyday places over the last week to see how co2 levels compared to those measured in quebec classrooms.
the measurements compiled are revealing. some settings are riskier than others for covid transmission, the readings show, and overall, it was difficult to find places that matched the co2 levels reported in schools.
on a 30-minute bus ride through the city’s plateau-mont-royal borough, for example, levels hovered between 500 and 600 ppm — not far from the typical outdoor reading of roughly 400 ppm.
during a morning métro ride, where most seats were occupied, readings ranged from 495 ppm to 719 ppm. an evening rush hour ride gave the same results, and there was no noticeable difference between older métro cars and the newer azur cars introduced in 2016.
readings also remained relatively low at a public library (486 ppm), at two downtown food courts (596 ppm and 768 ppm) and in a hospital emergency waiting room (687 ppm to 867 ppm).
a reading of 516 ppm at a métro station.
allen mcinnis
/
montreal gazette
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as expected, the highest levels were seen in smaller areas or crowded places.
two separate cafés yielded results of around 1,000 ppm. during a 30-minute haircut at a barber shop, where six people were present, levels climbed from 680 ppm to 1533 ppm.
at a crowded big-box retail store, readings peaked at 1,174 ppm, and levels were similar during two separate trips to a busy grocery store (928 ppm and 972 ppm).
a 20-minute car ride with two people — with the windows closed and air conditioning running — saw levels reach as high as 3,371 ppm. during a similar ride with the windows open, readings never reached above 600 ppm.
co2 readings over 2-hour period green recorded outdoors, orange in big box store, red in a car with windows closed.
since most elementary and high schools had yet to reopen, the gazette was not able to take a reading inside a classroom with students in attendance.
during two classes at a montreal-area cegep this week, however, levels reached 1,443 ppm and 1,823 ppm. during other classes, including one held in a gym, the readings hovered between roughly 550 ppm and 650 ppm.
according to the education department, last may more than 99 per cent of classrooms recorded an average weekly concentration below 1,500 ppm.
still, during the week of june 6, for instance, there were 172 classrooms with an average reading above 2,000 ppm, and 622 with an average of between 1,500 ppm and 2,000 ppm.
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the co2 readings also appeared to improve during warmer months, presumably as it became easier for teachers to keep the windows open.
the average weekly co2 concentration for all active monitors across the school network dropped from 917 ppm in late january to 696 ppm in late may.
since july 2020, quebec says it has invested $293 million to ensure schools are safer. another $225 million is planned to be spent this year.
the work has included calibrating ventilation systems, installing air exchangers and replacing or adding windows to ensure more can be opened. unlike other jurisdictions, quebec has opted not to add air purifiers to classrooms.
the education department uses the co2 readings to determine which schools need to take steps to improve air quality.
depending on whether a school has a mechanical ventilation system or not, it calls for any classroom with a daily average above 1,000 ppm to take steps to address the situation, such as opening the windows if possible.
if the daily average is above 1,500 ppm, the education department says an “intervention” is necessary to determine whether corrective work is required.
in an email response, the department said the 1,500 ppm threshold was agreed upon “by ventilation and public health experts.”
a reading of 468 taken outdoors at a downtown street corner.
allen mcinnis
/
montreal gazette
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but the department has also been criticized for how it calculates the readings.
on its website, it warns the data should be considered preliminary, as it includes results from periods or days where students aren’t in the classroom, which drives down the averages.
olivier drouin, a montreal-area father who has compiled covid-19 data in schools, began asking teachers to submit co2 readings from their classrooms last january.
drouin received a little over 200 readings during the next six weeks, at which point he says teachers were told by employers to no longer share data with him. during that time period, nearly 85 per cent of all the readings he received were above 1,000 ppm.
teachers submitted readings higher than 4,000 ppm on six occasions, all from different schools. the highest reading, 4,941 ppm, was recorded in a private high school classroom in the laurentians. the lowest, 406 ppm, was taken in a high school on the south shore.
drouin has urged the government to release the raw data behind the c02 measures it tracks, arguing that basing decisions on averages doesn’t make sense.
“if one afternoon, a classroom is at 4,000 ppm, it’s in that moment that you could be at risk of catching covid,” drouin said. “of course, there will be peaks and valleys, but it’s the peaks that are most important. because that’s when you’re breathing other people’s air.”
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bilodeau stressed the monitors should serve only as indicators and not as a solution.
though he welcomed the government opting to install them, he said the devices shouldn’t be considered a tool similar to air purifiers equipped with hepa filters.
“it’s a good first step, but it’s just highlighting the risks and the problems,” he said. “those still need to be addressed.”
he also agreed with drouin that averages don’t give an accurate picture of the situation and questioned quebec using 1,500 ppm as a benchmark.
“fifteen hundred is really high,” bilodeau said. “when you’re between 1,000 and 1,500 ppm, you’re in the range where the risk is steep. you don’t want to be there for nothing.”
asked about some of the readings the gazette took for this story, bilodeau said he wasn’t surprised levels were often relatively low.
the issue with classrooms, he said, is that they present the “perfect recipe” — a lot of people gathered in small spaces, often with poor ventilation.
to bilodeau, this ties into the larger issue with schools during the pandemic.
while people may be in places that are poorly ventilated at different points throughout the day — say, at a crowded restaurant for dinner — they’re usually there once, for a limited time.
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“but imagine you’re in a classroom with those levels for five or six hours. you’re there monday, tuesday, and up to friday. every day,” he said.
“the risk is accumulating.”
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