The COVID-19 pandemic has devastated the in-person meeting industry. Though it took too long to recognize that COVID-19 spreads via air transmission, we finally have effective procedures (vaccine mandates, masking, air quality standards, and social distancing) to reduce infection risk at in-person meetings. Now, meeting planners can add an affordable air quality tool to their site visits.

How can you determine air quality at a prospective venue?

Look around the room at an in-person event and you’ll see if masking and social distancing are taking place. We can implement vaccination mandates using third party vendors such as sharemy.health, CLEAR Health Pass, Safe Expo, and others. But how can we determine the air quality at a prospective venue?

Currently, we don’t know how to detect airborne COVID-19 viruses. (This is likely to be true for a long time. We still have no test for airborne tuberculosis bacterium (TB) transmission two centuries after identifying TB as a distinct disease.)

Luckily, under conditions I’ll outline below, we can obtain useful information about a venue’s air quality by using a device that measures a proxy for air pollution: carbon dioxide (CO₂).

People breathe in air, typically containing about 0.04% CO₂. They breathe out a mixture of gases containing about 4 – 5 % CO₂. People with COVID-19 co-exhale respiratory aerosols containing the SARS-CoV-2 virus.

If an occupied building space has effective ventilation, the occupants’ excess exhaled CO₂ is quickly diluted with fresh air, and the CO₂ level in the air remains close to normal values. Measuring the level of CO₂ in the air can, therefore, tell us whether effective ventilation is present or not.

Here are the generally accepted standards for CO₂ levels:

Until recently, meters that measure CO₂ levels in the air cost hundreds of dollars. (Some models with especially accurate sensors or the capability to measure other air pollutants still do.) But today we can buy an affordable air quality tool — a hand-held CO₂ meter for under $100. The one I just purchased (illustrated above) cost $80, and there’s a wide variety to choose from (for example, from here or here).

My 3.27″ (diameter) x 1.26″ (depth) meter measures CO₂ levels from 0 – 5,000 ppm. It can run on standby for 18 hours, supports USB charging, and includes a battery level indicator and temperature and humidity readings. While its specifications omit accuracy, inexpensive CO₂ meters are typically reliable within ±100 ppm. This is good enough to provide a decent estimate of the air quality in an enclosed space.

My unit shows a concentration of ~350 ppm CO₂ outside my rural Vermont home, which was built tightly. In my home office, the level increases to about 450 ppm, and rises to about 525 ppm if I’m sitting next to the unit for a while. Slightly cracking open a window quickly brings down the reading.

I haven’t had time to explore other buildings yet, but am looking forward to seeing what I find out when I do.

Is a CO₂ a proxy for indoor air quality in occupied spaces?

Can measuring CO₂ levels give us a useful indication of indoor air quality?

The answer is a qualified yes. It depends!

First of all, we need to measure CO₂ levels in occupied spaces. A meeting planner doing a site visit should take CO₂ readings in occupied meeting rooms, restaurants, hotel lobbies, etc. Taking measurements in empty spaces will only show high readings if the building ventilation system is grossly inadequate (with CO₂ infiltrating from other areas.) Also bear in mind that increasing the number of occupants in a space increases the likelihood that an infectious person will be present and the number of people possibly infected. Doubling occupancy can thus cause a four-fold increase in risk of transmitting COVID-19.

Second, there are sources of CO₂ that are not related to human exhalation but will increase meter readings. A common source is combustion emissions such as gas stoves, which can significantly increase CO₂ levels. Pets can also increase CO₂ levels, though animals are unlikely to be sources of the COVID-19 virus. Such sources will cause increased levels of CO₂ without increasing the incidence of COVID-19 transmission.

Finally, air treatment options, such as MERV 13 or better filtering, or possibly ultraviolet-C radiation, may reduce the prevalence of active COVID-19 aerosols. When venues employ these mitigation strategies, CO₂ levels will not be decreased. Of course, if a venue has deployed these preventative measures, they will surely inform you about them when asked!

Due to these factors, you shouldn’t rely solely on measurements of CO₂ levels to determine whether a space is ventilated enough to mitigate transmission risk.

However, a simple CO₂ meter like the one I now own can be an effective air quality tool, providing valuable information to anyone who wants to investigate the air quality of occupied spaces at venues, hotels and properties, restaurants, and other meeting locales. I’ll be bringing mine when I travel, and I encourage you to do this as well!

More information on the relationship between CO₂ levels and COVID-19 exposure

If you’d like to learn more about the relationship between CO₂ levels and COVID-19 exposure risk, here are some useful references:

• Can CO₂ sensors be used to assess COVID-19 transmission risk? by Canada’s National Collaborating Centre for Environmental Health.
• Role of Ventilation in Controlling SARS-CoV-2 Transmission by the Environmental Modelling Group of the United Kingdom’s Scientific Advisory Group for Emergencies (SAGE-EMG).
• Exhaled CO2 as COVID-19 infection risk proxy for different indoor environments and activities by Z. Peng & J. L. Jimenez.

And here are some less technical media articles on CO₂ meters:

• The coronavirus is airborne. Here’s how to know if you’re breathing other people’s breath from the Washington Post.
• The Hot New Back-to-School Accessory? An Air Quality Monitor from the New York Times.