Some Winnipeggers take to Twitter to opine on the Jets, the weather or politics.

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Some Winnipeggers take to Twitter to opine on the Jets, the weather or politics.

But a grassroots group is using the platform to post some unconventional reviews of movie theatres and sporting arenas.

In July, Matt Froese tweeted that the racing film F9: The Fast Saga was "brilliant, full stop," but he added that the McGillivray Boulevard cinema had 1,000 parts-per-million of carbon dioxide when the credits rolled.

That same month, he found the apocalyptic horror film A Quiet Place Part II to be "very good," with the St. Vital theatre having even-better ventilation, "still under 500 ppm CO2 by the end of the show."

Froese is among a handful of local residents who carry carbon-dioxide monitors around town to see how well indoor spaces are ventilated. They use the readings to try limiting their risk of being exposed to airborne coronavirus particles, and share their findings on social media.

Matt Froese holds the CO2 detection devices. (Mike Sudoma / Winnipeg Free Press)</p>

Matt Froese holds the CO2 detection devices. (Mike Sudoma / Winnipeg Free Press)

"It's an area of control, where people can kind of establish a sense of where they're at. And that's an attractive thing in a time when there's a lot of unknowns," says Froese, who works as a mechanical engineer.

"Monitoring CO2 inside can tell us how effectively we're diluting that exhaled breath, and how much of somebody's exhaled breath you might be inhaling."

The stuffy on city

In recent weeks, Winnipeggers have tracked concentrations of carbon dioxide in indoor spaces that suggest some are poorly ventilated, while others are quite airy.

Outdoors, CO2 concentrations are, generally, about 425 ppm, while indoors, 1,000 ppm is considered acceptable air quality.

In recent weeks, Winnipeggers have tracked concentrations of carbon dioxide in indoor spaces that suggest some are poorly ventilated, while others are quite airy.

Outdoors, CO2 concentrations are, generally, about 425 ppm, while indoors, 1,000 ppm is considered acceptable air quality.

Readings can vary based on many factors, and experts suggest focusing on long-term trends instead of single moments in time. Here’s a look at how sites around the city compare:

● 420 — opening windows to create a cross-breeze at home, after reaching 950 with visitors

● 500 ­­­­­­­­­­­­­­― A St. Vital movie theatre

● 525 ­­­­­­­­­­­­­­― An October show at the Centennial Concert Hall

● 550 ­­­­­­­­­­­­­­― Winnipeg's Richardson International Airport terminal

● 615 ­­­­­­­­­­­­­­― The Forks Market hall

● 775 ­­­­­­­­­­­­­­― Boston Pizza on McPhillips Street during a busy lunch

● 1,500 ­­­­­­­­­­­­­­― An hour into a Winnipeg Jets game from a seat inside Canada Life Centre

● 2,600 ­­­­­­­­­­­­­­― A men’s washroom at Canada Life Centre

● 2,100 ­­­­­­­­­­­­­­― A community centre in St. Vital, after 15 minutes of youth sports

Experts list a handful of caveats to accurately tracking carbon dioxide, and add that it’s not a direct proxy for assessing COVID-19 risk. Yet a growing body of evidence suggests CO2 readings can be a tool for limiting the risk of spread, along with masking and distancing.

It all has to do with ventilation, which is when stale air is filtered or replaced with fresh air, which dilutes particulate matter instead of circulating it throughout a room. While the coronavirus spreads in droplets, it also can be suspended in the air in tiny particles known as aerosols — especially from people who aren’t wearing masks.

That’s led some people to buy hand-held CO2 sensors, each costing $300 to $600, to measure the parts per million (ppm) inside various venues.

A CO2 detection device. (Mike Sudoma / Winnipeg Free Press)</p>

A CO2 detection device. (Mike Sudoma / Winnipeg Free Press)

Froese has taken a CO2 detector everywhere from The Forks to aboard a flight. It was particularly useful at his church, where he learned there was good ventilation inside the main prayer area, but the lobby had higher CO2 levels.

At work, his colleagues tweaked their ventilation system to run longer, after noticing a spike in CO2 at the end of the day.

And he learned that many restaurants are better ventilated than the average home, which he chalks up to often being located in newer buildings.

"We're all in this sort of in-between phase, where a lot of us would like to get back to normal as much as possible, but a lot of people are still very cautious in how to go about that," he says.

Canada’s National Collaborating Centre for Environmental Health notes that research is still underway on how well CO2 readings correlate to COVID-19 risk.

Before the pandemic, carbon-dioxide readings were largely used to avoid stuffiness, such as distracting smells. Building codes require ventilation in new builds, but don’t often mandate followup inspections.

The research, summarized by environmental health scientist Angela Eykelbosh, says that there isn’t a widely accepted measurement of CO2 ppm to know when a building is COVID-safe. Instead, the devices can clarify how many people it takes for a room to get stuffy and actions that improve ventilation.

She says anyone using a CO2 sensor should keep it at an adequate distance from windows and other people, and use a monitor that records trends over time, instead of taking a single reading.

CO2 readings can fluctuate drastically in the presence of pets or combustion, such as a candle or burning food, neither of which impact the presence of coronavirus, she says.

Meanwhile, COVID-19 risk can also fluctuate in ways a CO2 detector might not detect, such as by releasing more aerosols from a singer, or when a "super-emitter" ­­­­­­­­­­­­­­― someone who sheds much more of the virus than the average infected person ­­­­­­­­­­­­­­― is present.

Proper masking doesn’t drastically change CO2 readings, but it has a huge impact on COVID-19 spread.

Froese has his own caveats, based on his engineering work.

For one, buildings maintain room temperature by sucking in cool outdoor air until early autumn, but that ceases when the outside air gets too cold. That means there’s less ventilation now than what was recorded a month ago.

He says ventilation is among the many tools that help reduce COVID-19 ­­­­­­­­­­­­­­― alongside masks, vaccines and distancing ­­­­­­­­­­­­­­― and it's not a magic bullet.

"It tells us about one piece of our layered protection," he says.

"People are looking for a sense of reassurance about where they can spend their time safely." ‐ Matt Froese

Still, the state of Washington decided early this year to use CO2 sensors to determine whether dining areas qualified for higher-capacity limits. The policy, which held until July when officials scrapped indoor restrictions, allowed gatherings inside when readings were below 450 ppm.

In Australia, a Twitter account called CO2 Guerrillas leans on crowdsourced readings to "help make crappy air quality visible."

These detectors have been rolled out in studies of Ontario and Quebec classrooms to monitor things such as the impact of opening windows.

As a fourth wave of COVID-19 takes hold in Manitoba, teachers have started using the devices in their classrooms after doctors criticized the province for not monitoring indoor air quality in schools.

Winnipeg teacher Lauren Hope is shelling out $500 for a CO2 sensor. Once it arrives next month, she hopes it will yield answers officials won't provide on ventilation inside her own classroom, as well as at both her kids' schools.

"For my own piece of mind, it’s like an early warning sign if we were out somewhere, that maybe this is not as safe of a space that it’s meant to be," says Hope, who is also going to use the sensor to plan outings with a high-risk family member.

She's mystified that Canadian officials have been reluctant to explain the growing evidence of airborne coronavirus.

"It's frustrating to know that (there are) regular folks out there who think they are doing everything they can to stop the spread of COVID," she says.

"We really need to pivot away from the hygiene theatre of sanitizing and Plexiglas, and... address air exchange,"

“For my own piece of mind, it’s like an early warning sign if we were out somewhere, that maybe this is not as safe of a space that it’s meant to be." ‐ Lauren Hope, teacher

Kim Prather, an aerosol scientist at the University of California, San Diego, argues schools should use CO2 sensors alongside particle monitors to reduce the amount of coronavirus and influenza circulating in classrooms.

"This is the silver lining of this pandemic. If we can improve indoor air quality, we can increase attendance, attention (and) test scores," she told a University of Toronto panel last week.

"That's what good schools should be doing."

Some American schools and businesses have fashioned air purifiers out of box fans and furnace filters in what's become known as a Corsi-Rosenthal cube.

"People just took control, and said we are not helpless," Prather says.

Froese says as the number of cases has increased again during the current wave people have become more anxious.

"People are looking for a sense of reassurance about where they can spend their time safely," he says.

dylan.robertson@freepress.mb.ca