Canadian wildfires are once again polluting the air in multiple U.S. states, as they did last June when New York City briefly had the world’s worst air quality, which caused, among other major problems, a spike in asthma-related medical emergencies across the city over several days.
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But we should not worry only about outdoor air because dirty air creeps indoors thanks to cracks, inadequate sealings, and poor ventilation. That’s on top of indoor air quality (IAQ) that is already bad in old buildings—like a great many schools—because of antiquated and poorly maintained ventilation systems and filters. One-third (36,000!) of public schools in the U.S. needed to update or replace their outdated heating, ventilation, and air-conditioning systems according to a 2020 government study.
To deal with the risk of acute wildfire exposure, a ventilation system, a.k.a. HVAC, can be temporarily shut off as local governments often urge. But a much better strategy is to install good indoor filtration (including MERV13 filters as recommended by EPA) since the biggest air pollution threat to our children—and our teachers—isn’t actually the acute exposure during wildfires, but the chronic exposure to bad air they get over the entire school year. Children are particularly threatened by this chronic exposure because their lungs are still developing.
Research finds that poor ventilation in schools increases student absenteeism and worsens acute asthma attack symptoms. Furthermore, EPA reported in 2023, “Children in classrooms with higher outdoor air ventilation rates tend to achieve higher scores on standardized tests in math and reading than children in poorly ventilated classrooms.”
One way to determine air quality at your child’s school and to improve health—and school performance—is to place a low-cost CO2 monitor in every classroom. This would also help protect our teachers and school workers from the dangerous impacts of pollutants, including small particulates increasingly linked to dementia.
Carbon dioxide is the most easily monitored indicator of indoor air quality and is a good proxy for the overall rate of outside air ventilation, according to many studies. In fact, most modern HVAC systems today use “CO2-based demand control ventilation,” which means they have built-in CO2 monitors that trigger higher ventilation rates when CO2 levels hit a specific set point.
Monitoring classroom CO2, it’s clear when it hits levels linked to impacts on human health or cognition. According to the 2,200-page Handbook of Indoor Air Quality from 2022, “Present studies show that to ensure classroom IAQ conducive to learning, CO2 levels … should be kept below 900 ppm [parts per million] at all times.”
A 2017 review of two dozen global studies found that most classrooms averaged over 1,000 ppm, “with maximum values ranging from 1,400 ppm to 5,200 ppm.” Harvard researchers have found that even 1,000 ppm can harm human cognition with impacts rising sharply at 1,400 ppm and beyond.
When monitored CO2 exceeds recommended levels, teachers can take short-term measures, like opening a window, if possible. They should also keep the doors open between classes to help flush out the air.
But if the air is persistently above recommended levels, the school needs to increase the ventilation rate—and very possibly replace an antiquated or poorly maintained HVAC system.
While children are most at risk from bad indoor air, everyone should be concerned. EPA reports, “Indoor levels of pollutants may be two to five times—and occasionally more than 100 times—higher than outdoor levels.” I often keep a portable CO2 monitor with me and have found a medical exam room at 1,800 ppm, an Amtrak train at 1,900, and an apartment at 1,600.
If you suspect your office’s indoor air quality is subpar you should also get a CO2 monitor. “Humans are pretty good sensors of high CO2 levels,” Carnegie Mellon University’s Vivian Loftness told me. Her research shows occupant perception of indoor air quality drops sharply as CO2 levels rise from 600 to 750 ppm.
Beyond CO2, other pollutants pose serious problems. A 2022 study in Neurology, “Air Pollution and Incidence of Dementia,” reviewed 20 studies looking at pollutants like fine particulate matter smaller than 2.5 microns (PM2.5, a.k.a. soot). As PM2.5 concentrations rose, so did the risk of dementia. A 2023 study found higher PM2.5 levels in people’s homes were linked to higher rates of dementia. Recent studies also find higher PM2.5 levels are associated with lower standardized test scores.
Unsurprisingly, PM2.5 reduction is emerging as an important strategy for minimizing dementia risk—especially in areas prone to wildfires. Unfortunately, climate change is worsening the wildfires and increasing the length of the wildfire season.
With schools newly out or nearly out for summer across the country, now is the time to present these questions to principals and teachers. Investing in CO2 monitors as a starting point will reveal potential next steps. Energy-efficient and nonpolluting electric heat pumps with advanced filters and demand-control ventilation are the best choice for a new HVAC system to improve air quality. They can provide three to four units of heat for each unit of electricity consumed and can also provide cooling. They are so cost-effective they have outsold natural gas boilers for the last two years. Groups like the Climate United Fund have billions of dollars to support such projects, especially in low-income and disadvantaged communities.
As an extra benefit, heat pumps don’t burn natural gas, which contributes directly to bad indoor (and outdoor) air and climate change—and hence to worsening wildfires.
Learn more about Moms’ work on schools.
Joseph Romm is Senior Research Fellow at the University of Pennsylvania Center for Science, Sustainability, and the Media. He is a former acting assistant secretary of Energy Efficiency and Renewable Energy.
Tell the House: Support the Indoor Air Quality and Healthy Schools Act