Health Advice



I used a $150 device to track my COVID risk. I got COVID anyway

Emma Court, Bloomberg News on

Published in Health & Fitness

The monitor frequently showed a number that was higher than the Centers for Disease Control and Prevention’s recommended benchmark for indoor air quality of 800 ppm – in fact, about 60% of my readings over the course of a month exceeded that number.

At restaurants, in taxicabs and on airplanes I watched the digits climb to worrisome levels, but also at people’s houses, in a hotel room and at a store. Sometimes, the readings were several times higher than 800 ppm.

Those numbers were a signal not only that I was in poorly-ventilated spaces, but also that I was breathing in the potentially COVID-laden air that other people were exhaling. At one point, while in a car with the windows closed and AC on, nearly 10% of what I was breathing in had been exhaled. My carbon dioxide monitor actually tells me exactly how much that is happening.

If you’re in a space with high carbon dioxide levels, says Marr, you may want to put on a high-quality mask or try and minimize time in that place.

Some of the highest readings on my travels were taken as the flights I was on were boarding. While you hear a lot about airplane filtration, those systems often aren’t running until the airplane starts moving.

“We’ve been warning about this,” said Joe Allen, an associate professor at the Harvard T.H. Chan School of Public Health and another carbon dioxide monitor-carrying public health expert.


The carbon dioxide monitor’s readings were also high in flight, but that turned out to reflect one of the device’s limitations: It measures ventilation, but not filtration. On airplanes, air is recirculated, so you are breathing in a lot of air that other people have breathed out, but that air is also going through a high-quality filter, so it is unlikely to contain virus particles, said Marr.

Limitations aside, my device’s readings were consistently high in many kinds of places. Allen said this is because good ventilation just isn’t generally a high priority — though he sees that changing now, two years into a global pandemic that has killed more than 1 million Americans. Improving indoor ventilation doesn't have to be difficult or expensive, either. It can be as simple as opening windows or installing high-quality filters in an existing HVAC system.

And fresh air doesn’t just reduce COVID risk. It can also help reduce the contaminants that build up from such things as pet allergens, mold and chemical cleaning products — all stuff you don’t exactly want to breathe in either. There’s even a name for illness caused by poor ventilation: sick building syndrome.

Places that I didn’t manage to get to during my travels, like Boston’s public schools (where Allen has served as a ventilation advisor) and entertainment venues in Japan, are making information about air quality more widely available. Belgium has gone even further, requiring visible carbon dioxide monitors in public settings.


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