This scientist says cleaning indoor air could make us healthier—and smarter

By Douglas Starr 

Joseph Allen runs a major public health research project at Harvard University, probing how indoor air quality affects human health and cognition. He consults with companies on ventilation and air filtration, and during the pandemic he became a prominent voice on public health, writing dozens of op-eds criticizing early guidance from health authorities and debunking misconceptions about how the virus spreads.  

Air intakes on Boston’s Prudential Center loom over Joseph Allen, who stresses the need to draw more outside air into buildings.


“Joe has always had a unique understanding of this range of domains—from how buildings work, to environmental exposure assessment, to making connections with health outcomes,” says Brent Stephens, chair of the Department of Civil, Architectural, and Environmental Engineering at the Illinois Institute of Technology. “There’s not a tremendous number of people in this world that have worked on that whole spectrum.”

When the COVID-19 pandemic arrived, the previously esoteric field of indoor air quality suddenly became the focus of widespread concern. Like many of his colleagues, Allen jumped into the fray, advising school systems, police departments, entertainment companies, the Boston Symphony, and a host of other entities on how to make their indoor air healthier, during the pandemic and afterward.

“COVID really changed the conversation,” says Matt Murray, vice president of leasing at Boston Properties, the largest publicly traded developer in the United States and one of Allen’s consulting clients. Before the pandemic, the company would have to explain to bored executives why they should pay attention to indoor air. “Now, the CEOs are all saying, ‘What filters do you use? How you process the air you bring into the workspace?’” Murray says. “And we’re ready for those conversations because we’ve been working with Joe.”

The idea of a healthy building has been made too complicated.

Joseph Allen and John Macomber, Harvard University

In 2014, Allen accepted a position at Harvard, where he soon turned his attention to how the indoor environment can affect people’s cognitive abilities. Many of us have struggled to pay attention during a long staff meeting in a stuffy conference room. Research by Allen and others suggests that lassitude may not be due solely to boredom, but also to the carbon dioxide (CO2)-rich conference room air.

Ever since the energy shocks of the 1970s, buildings in the United States have been made as airtight and energy-efficient as possible. The result was a buildup of toxic volatile organic compounds (VOCs) and exhaled CO2. “Green building standards” introduced in the late ’90s focused on reducing toxic materials and making buildings healthier as well as more sustainable, but they didn’t prioritize indoor air quality and ultimately did little to improve it.

In a multiyear series of experiments, Allen and his team have investigated the consequences. In the first study, published in 2015, they had 24 white-collar volunteers spend six working days in environmentally controlled office spaces at Syracuse University’s Total Indoor Environmental Quality Laboratory. On various days the experimenters would alter ventilation rates and levels of CO2 and VOCs. Each afternoon the volunteers were tested on their ability to think analytically and react to a crisis. (One test, for example put the volunteer in the role of a small-town mayor trying to react to an emergency.) All tests were double-blind: Neither the volunteers nor the study personnel knew that day’s environmental conditions.

The results were dramatic. When volunteers worked in well-ventilated conditions (which lowered the levels of CO2 and VOCs), they scored 61% higher than when they worked in typical office building conditions. When they worked in the cleanest conditions, with even lower CO2 levels and higher ventilation rates, their scores climbed 101%.

To find out whether the results held up in the real world, Allen and his team recruited 109 volunteers from 10 office buildings across the United States. Six had been renovated to create better heat and humidity control, improve ventilation, and lower the use of toxic materials. Four had not. Allen’s team gave each office worker a Fitbit-like bracelet to record heart rate, skin temperature, sleep patterns, and other physiological signs of well-being. Workers also completed a survey each day about how comfortable they felt and whether they experienced symptoms such as drowsiness or headaches. At the end of the week, they took the cognitive tests. Workers in the buildings with good ventilation and lower levels of indoor pollution scored 26.4% higher than those in the unimproved buildings. They also reported sleeping better and experiencing fewer “sick building” symptoms.

Something in the air

Many sources of indoor air pollution can affect human health and cognition. These include particles and gases emitted by furniture and building materials, as well as carbon dioxide (CO2) exhaled by a building’s occupants. Choosing better materials and improving ventilation, filtration, and air processing can help make buildings healthier.

  1. Outside air is often the best way to ensure indoor air quality. The recommended exchange rate of four to six room changes per hour can be achieved by opening windows or tuning the ventilation system.
  2. Outdoor pollutants in areas with high levels of air pollution, experts recommend a high-quality filtration and air treatment system.
  3. Recirculation. Conventional forced-air heating and cooling systems recirculate the same air. Better filters and bringing outside air into the ventilation system or opening windows helps improve air quality.
  4. Off-gassing. Rugs, upholstery, paints, and cleaning materials can give off volatile organic compounds (VOCs), which can cause irritation and health problems. Choosing better materials is the best approac
  5. Exhaled C02. A buildup of CO2 because of poor ventilation can cause drowsiness and impair cognition. Outside air and a well-tuned ventilation system can address that concern.
  6. Resuspension. Routine activities such as walking on rugs and plopping down on chairs can raise levels of dust, which can carry pollutants. Better air filtration and cleaning surfaces with vacuums with built in filters.

Size matters. Of the many particles found in indoor air, exhaled particles smaller than 5 micrometers (μm) have become a focus during the COVID-19 pandemic because they can linger in the air and transmit disease.

This is really important, interesting work,” says Elliott Gall, an indoor air scientist at Portland State University. “It’s a great example of the kind of interdisciplinary work [that explores] the complexity of indoor air and how it affects us.”

Over time, Allen came to see businesspeople as natural allies who could act on his public health findings faster than government officials. He teamed up with John Macomber, a Harvard Business School lecturer and former CEO of one of the largest construction companies in New England. Macomber was impressed with Allen’s research suggesting a tiny sacrifice in energy efficiency through improved ventilation could increase a business’s bottom line by as much as 10% by decreasing absenteeism and boosting worker productivity. “I realized we’ve been missing the boat,” Macomber says. “We’re chasing pennies on energy when there’s thousands of dollars in productivity issues.”

Allen and Macomber consulted with companies and spoke at corporate conferences, making the economic case for improving ventilation and filtration as well as adjusting lighting, temperature, and humidity. “The idea of a healthy building has been made too complicated,” they wrote in a book they co-authored, Healthy Buildings: How Indoor Spaces Drive Performance and Productivity. “There are just a handful of things we need to do to make a building healthier.”

Allen’s group continued to investigate how the indoor environment affects our mental state. They found that airline pilots exposed to CO2 levels common in cockpits did worse on Federal Aviation Administration–mandated emergency response tests than when they breathed better air. They showed that during a heat wave, students who lived in non–air-conditioned dorms had slower reaction times and poorer problem-solving skills than those with air conditioning. They showed that bringing plants and views of nature into the workplace can lower office workers’ heart rate, blood pressure, and other physiological indicators of stress.

In 2019, Allen’s team embarked on an ambitious international project to examine the long-term impacts of indoor air quality by tracking the physical and cognitive health of more than 300 office workers in 43 buildings in six countries over the course of 1 year. They mailed each worker a wristband to monitor their physiology and a small sensor to continuously measure levels of fine particulates and CO2 in their workspace. At predetermined times and levels of CO2 and particulates, the program pinged each worker’s smartphone with a quiz to test reaction time and cognitive function. The studies showed that in offices across the world, poor ventilation, CO2, and particulates (which carry VOCs) conspire to significantly impair cognitive function.

WHEN THE FIRST REPORTS of the new coronavirus emerged from Wuhan, China, in January 2020, Allen realized his years researching air quality and disease transmission in indoor environments had new relevance. “Even though the virus was novel, there are elements in all this that feel quite familiar,” he says. “It doesn’t matter if it’s a radiological hazard, biological hazard, or chemical hazard. We know how to assess the risk and put in appropriate controls.”

Early in the pandemic, experts at the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) latched onto the idea that the virus was spread by large, exhaled droplets that float for a short time and then settle on surfaces. But scientists specializing in aerosols knew airborne viruses are more likely to ride on tinier particles exhaled when people breathe, sneeze, cough, or talk. Smaller than 5 microns, these particles can travel across a room and linger in indoor air for hours.

Aerosol experts such as Lidia Morawska of Australia’s Queensland University of Technology, Gardens Point; Donald Milton of the University of Maryland, College Park; and Linsey Marr of Virginia Polytechnic Institute and State University argued that the focus on larger droplets had led to wrong-headed guidance about washing packages with bleach, staying 2 meters apart—even outdoors—and other forms of what some researchers called “hygiene theater.” They urged policies that emphasized indoor mask wearing and less draconian regulations for people outdoors, where the virus would quickly disperse.

Allen signed on to that fight, collaborating with aerosol experts and public health researchers on scientific papers and bringing their case to the public. “He’s a really good public communicator,” says Marr, who credits Allen with helping her work get the attention it deserves.

“One of our biggest frustrations over the past year is that we knew enough to act early on,” Allen says. “Even by late January 2020 we knew that airborne transmission of aerosols was not only likely, but probable.” Waiting for proof made no sense. “This was a pandemic, an all-in moment, so why wouldn’t we have immediately deployed every strategy that could have helped?” Those strategies, Allen knew from his research, include bringing more outside air into chronically under ventilated buildings and using higher efficiency (air) filters in ventilation units.

One of our biggest frustrations over the past year is that we knew enough to act early on.

Joseph Allen, Harvard University

The new focus on indoor air quality could help hasten the end of the current pandemic and perhaps even help forestall the next one. It may bring broader changes as well. Businesspeople are recognizing the value of improving indoor air to create better working conditions and add value to their properties. “What we’re seeing with some parts of the market—notably the higher end, real estate investment trusts, owners of multiple office buildings or apartments—is they’re thinking really hard about competing” in the post pandemic market, Macomber says. “And one way to compete is to have healthier buildings.”

Allen predicts that the new availability of cheap personal air quality monitors will quicken that competition and heighten people’s awareness of the indoor environment. Previously, the only way to assess indoor air quality was to hire an expensive consultant. Now, with monitors available online for less than a couple of hundred dollars, any office worker or hotel guest can quickly monitor CO2; some devices even detect VOCs. If consumers post results on websites like Yelp, businesses would be forced to pay attention. (Indeed, some building owners already boast about air quality in advertisements.)

“I think there’s going to be a fundamental rebalancing in terms of how we think about indoor spaces,” Allen says. “I think that people won’t tolerate sick buildings, where you feel tired, your eyes itch, you have a headache, or you’re stuffed into a closet like office with no windows.” It’s one lasting positive from the pandemic. “That era is over,” Allen says. “Rightly so, and good riddance.”

Posted in: Health doi:10.1126/science.abl8715

Douglas Starr is a journalist in Boston

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