Opinion | Why more virus-free air could be coming to schools and offices

Although it wasn’t widely understood when the pandemic began, virus particles spread person-to-person when exhaled in both larger droplets that fall to the ground and smaller aerosols that hover for hours. Clouds of virus particles do not disperse easily in stagnant indoor air. Just recall the dark days of the pandemic, when the virus stalked cruise ships, church choirs, prisons, meatpacking plants and other tight, enclosed spaces. Outdoors, the air moves faster and virus particles dissipate more quickly.

Most buildings in the United States were constructed to meet minimal air quality standards unsuited to mitigating respiratory disease. According to Joseph G. Allen, an associate professor and director of the Healthy Buildings program at Harvard’s T.H. Chan School of Public Health, this “sick building” problem long predates the pandemic but the pandemic experience is helping to accelerate change. It showed that simple improvements such as bringing in more outside air, upgrading filtration and enhancing ventilation slow disease spread. “Healthy” buildings can also reduce the transmission of other respiratory ailments, including influenza and RSV; can help reduce asthma exacerbations and allergy symptoms; and can improve cognitive functioning for people working and studying in them.

The CDC previously recognized the importance of improving air quality, but on Friday the public health agency published revised guidance that for the first time prescribed a specific target of five air exchanges per hour. This means supplying, or exhausting, the amount of air in a space five times over the course of an hour. The target can be met in different ways — with a combination of outside air and improved filtration and ventilation. While the new target “will not guarantee totally safe air in any space,” the CDC says “it reduces the risk of exposure to germs and other harmful air contaminants.”

Likewise, most buildings in the past were equipped with filters known as MERV-8 that are designed to protect equipment and capture about 20 percent of airborne particles. The CDC has now called for buildings to install MERV-13 filters that can capture 80 to 90 percent of particles. Also significant, the standard-setting American Society of Heating, Refrigerating and Air-Conditioning Engineers has completed and published a draft of its first-ever standard for maintaining healthy indoor air quality, with a final draft due this summer.

Although substantial pandemic-era funding remains available, a CDC survey of U.S. schools conducted from August to December last year found only a patchwork of ventilation improvements. Many schools were built to accommodate only three air exchanges per hour. Mr. Allen suggests that buildings first be given a “tune up” to check performance, then maximize outdoor air and upgrade filters, which are inexpensive.

Ultimately, the issue is not only about particles and filters. It will be up to businesses, workers, students, parents, scientists and everyone else to demand change in the buildings in which they spend so much of their lives. Do you know the air exchanges per hour at your workplace or classroom? The CDC is now giving us a yardstick to measure by. Americans should use it.