In May 2021, the residents of a 1960s-vintage slab-style apartment building called Rebecca Towers in Hamilton, Ontario, found themselves in the jaws of a rapidly worsening COVID-19 outbreak. That month, according to Hamilton Public Health, cases were identified in seventeen units on ten floors. More than 100 tenants eventually tested positive, and one died. With the pandemic into its second year, outbreaks in large residential buildings were by no means unusual, but this one sent shock waves beyond the city.
Frightened tenants staged rallies, appealing to the city’s public health officials to set up a mobile vaccination clinic on their street. (The city offered to expedite vaccinations for the building residents at another location.) Residents also accused the property managers of neglecting the routine upkeep of the ventilation systems; photographs shared online showed air ducts clogged with junk left over from renovations. “A lot of these repairs date back to before the pandemic,” Richard Weiss, a tenant, told the Hamilton Spectator.
Yet public health officials hewed to standard explanations about the outbreak: that the virus spread through contact among family members and because of inadequate social distancing in places like the laundry room, elevators, or corridors. During a media briefing on May 10, Elizabeth Richardson, the city’s medical officer of health, reiterated her department’s position and proffered advice that had become virtually boilerplate during the pandemic: “We look at making sure that people are aware of the requirements around physical distancing in those settings, [and are] aware of the requirements around masking in those settings.”
No one will ever forget the devastating reports from early in the pandemic, when COVID-19 tore through nursing homes, killing thousands of vulnerable seniors living in so-called congregate settings. As the outbreak continued, there were more revelations about elevated infection rates in lower-income or marginalized communities, including among those living in large apartment complexes.
But public opinion about the causes of these outbreaks focused on social determinants, such as the fact that many lower-income people couldn’t work from home, lived in crowded conditions, or lacked the time, language skills, or education to seek out vaccinations or practise adequate social distancing. Public health messaging, in turn, stressed behavioural practices: mask wearing, social distancing, hand washing, caution with gatherings. There was little mention of how the structure of buildings might contribute to transmission.
The contentious question posed by outbreaks such as the one in the Hamilton apartment complex is whether and how SARS-CoV-2 (the virus that causes COVID-19) spreads beyond the circumference of a sneeze and whether it is able to travel—intact and contagious—in the form of tiny airborne particles as well as in comparatively heavier respiratory droplets. The latter implicates the behaviour of individuals, whereas the former, so-called aerosol transmission, suggests that this lethal virus can circulate freely in the air of the buildings where we live, work, and recreate. These are radically different scenarios, grounded in two disciplines that clashed during the pandemic: medical science and building science. As one building-science expert told me, it was “almost a religious debate.”
Infection-control experts, including doctors and epidemiologists, have driven the public health response throughout the pandemic. The concern over airborne transmission took flight in July 2020, when 239 scientists sent an open letter to the World Health Organization, calling for more attention to this particular source of risk. Yet it took the US Centers for Disease Control and Protection (CDC) almost a year and a half of the pandemic to publicly acknowledge that aerosol transmission was, in fact, a genuine vector of contagion. The WHO held out even longer and conceded this explanation only on December 23, 2021, just as the first Omicron wave had begun to crest. The official size difference between aerosols and droplets is scant—five microns is the arbitrary dividing line—and the air in spaces where people have fallen ill contains both. But aerosols, because they are very light, can travel farther and remain airborne longer.
Through much of the pandemic, many infectious-disease experts and public health institutions have been extremely reluctant to acknowledge that the air in our buildings—places where we spend 90 percent of our time—may be making us, or some of us, sick. Advocating for masks and six-foot separation is one thing. But how do you cure a sick building? In a devastating global health crisis, that question turned out to be radioactive, a third rail. But the answer could completely transform the way we manage indoor air quality, arguably the most neglected part of building design.
When epidemiologist and University of Toronto professor Colin Furness was about eleven, he had a job selling newspaper subscriptions. He’d go to apartment buildings around Toronto, press all the buzzers until someone opened the door, and then work the floors looking for customers. “You’d smell everyone’s cooking, and it was obvious that air was being shared,” he says. “Those cooking smells were a constant.”
Apartment hallways redolent of cooking smells—or second-hand smoke, pet odours, or other indistinct scents—revealed to Furness something more than just the atmospherics of communal living. In almost all older buildings, corridors are an integral part of the ventilation system: slightly pressurized air is pumped into hallways lined with apartment doors that have a gap of a centimetre or two at the bottom. Ideally, the air flows under the doors and into apartments. There, fans, in bathrooms or above stoves, will pump it out.
But, under certain conditions, the air pressure in the halls falls below the levels in the apartments, meaning air from individual units flows back into the corridor and then potentially into other living spaces. Or, if the wind is blowing a certain way, an apartment’s air might flow out of open windows or balcony doors, rise, and then waft back into the apartments above. Air can also course through stairwells, often upward (hot air rises)—a phenomenon known as the “stack effect” that’s typical in cold climates. Often, that air will be recirculated. In other words, whatever scent is floating around in one apartment—some weed, last night’s fish dinner, the cat’s litter—can easily find its way into another one. What’s more, the crud that accumulates on the filters found in the heating systems of any building is a testament to the fact that airborne particles of all sizes can travel a long way through the internal circulation networks of ducts.
Furness’s field is infection control. For a part of his career, he focused on hand-washing protocols in hospitals. One of the pioneers in this field was Ignaz Semmelweis, a Hungarian physician known as the father of infection control. In 1847, working in a Viennese obstetrics ward, he observed that women receiving gynecological exams from physicians and medical students, compared with those being cared for by midwives, were far likelier to die from a type of sepsis. After some sleuthing, he found the reason: the doctors and medical students had been working on cadavers in the morgue before examining their patients. At his hospital, he demanded they wash and disinfect their hands before coming into the obstetrics ward, an intervention that proved to be a major turning point in the history of public health and hygiene, even though Semmelweis’s solution was highly controversial in its day and not widely embraced in his lifetime. The medical authorities, says Furness, “weren’t able or willing to make sense of this clear evidence.” The doctors, he adds, were in denial: “They all would have had to say to themselves, ‘I’ve been killing people for decades.’” It’s a reaction he saw in the public health response to the prospect of airborne transmission of COVID-19, a response which stressed that behavioural changes—using cloth masks or maintaining social distancing—were sufficient preventative actions.
The latter part of the nineteenth century saw dramatic reforms in public health, hygiene, and urban infrastructure. Scientists unravelled the mechanics of infection and chipped away at long-held beliefs, such as “miasma theory,” or the notion that bad smells spread disease. The historical context is key: the rise of industrial cities, with their overcrowded slums, heavily polluted air, and contaminated water, gave rise to cycles of deadly outbreaks of infectious diseases like cholera, typhoid, and tuberculosis.
In London, UK, where the Thames River had become an open sewer, a heat wave in 1858 triggered what came to be known as “the great stink.” In New York, meanwhile, thousands of poor immigrants lived in windowless tenement buildings with no airflow. Governments realized they had to act because air, the substance we all need most of all to survive, had become fetid and unbreathable. London confronted the condition of the Thames with a massive sewer-building program designed to shunt wastewater downstream, while New York passed new bylaws restricting the practice of building apartments without ventilation shafts.
Melanie Kiechle, a historian at Virginia Tech, has documented the way bad smells influenced urban life in the United States. She cites the example of how the US Sanitary Commission and the work of nursing pioneer and statistician Florence Nightingale helped improve ventilation in US Civil War field hospitals as a means of reducing mortality. Another important figure was a public health reformer named John H. Griscom, a New York physician and author of The Uses and Abuses of Air, an 1848 monograph. “One of the things that he was especially concerned about was the air inside of tenements,” she says. “He was pushing to have ventilation in all of these buildings to make sure that the ventilation was sufficient.”
Griscom and other scientists made elaborate calculations about room size and occupancy to determine minimum ventilation standards. “There had been at that point fairly recent discoveries about respiration, what happens when we breathe,” Kiechle says. “One of the key things that he learned, that I think applies to today as well, is how when we exhale, that air is exhausted. He used the word ‘vitiated,’ which means ruined.” In effect, generations before the advent of the modern office building, Griscom could explain why it’s so hard to stay awake and focused in cramped meeting rooms. “They were discussing what kind of ventilation systems buildings needed, particularly larger buildings like churches and theatres,” Kiechle says. “And Griscom was applying that to tenements as well.”
There was, Kiechle notes, an element of irony to these advances: “People were doing the right thing for the wrong reason.” A foul odour from an overflowing outdoor privy wouldn’t make you sick per se, but the smell explained the conditions that did: for example, raw sewage leaching into a nearby well, as the famous British epidemiologist John Snow discovered when he traced the cause of a cholera outbreak in London in 1854. Similarly, the buildup of carbon dioxide—identified as early as the 1750s—in a dank and crowded tenement cellar does not cause tuberculosis, but the associated lack of fresh air certainly helps the disease spread. “Bad air, of course, doesn’t have to have a smell,” Kiechle says. “But, often, what people understood is that if the air smelled bad, then there was danger in the air.”
By the early twentieth century, thanks to decades of transformative advances in hygiene, germ theory, civil engineering, and public health, the indoor atmosphere of buildings had improved substantially. Plumbing and modern sewers shunted away human waste. Municipal authorities were becoming more proactive in regulating aspects of building design, especially those relating to health and fire safety. Experts in the emerging field of “ventilation science” were laying out basic principles such as bringing fresh air indoors, expelling gas or smoke from cooking surfaces, and so on. Architects and building engineers developed air conditioning and heating systems. And, before antibiotics, tuberculosis patients were treated, in part, by exposure to fresh air, which was considered to have healing properties.
In the late nineteenth and early twentieth centuries, as civil engineering and public health practices stamped out deadly infectious diseases like cholera in western Europe and North America, the political energy around air quality shifted from indoors to outdoors. Severe air pollution—caused by smokestack emissions, leaded gasoline, solid-waste incineration, and coal used in home heating—triggered crisis conditions in places like Pittsburgh (1940s), Los Angeles (1950s), and Toronto (1980s). In London, atmospheric inversions and the prevalence of coal furnaces produced frightening episodes of air pollution. After the Great Smog of London in 1952, during which an estimated 4,000 people died and tens of thousands were hospitalized, the British government passed clean-air legislation. Scientists began to chart the devastating impact of tiny particulates, later known as PM2.5, on respiratory health. And, in the US, in 1970, president Richard Nixon signed the Clean Air Act, a law that gave the federal government sweeping powers to improve outdoor air quality. Canadian governments followed suit, with requirements for unleaded gasoline, scrubbers on smokestacks, and later measures including the phasing out of coal plants for electricity generation—a move that played a role in reducing smog advisories in Ontario. By the 1980s, public interest in indoor air quality (IAQ) had all but dissipated.
Until the COVID-19 pandemic, we rarely thought about IAQ as a serious health threat. Public concern about it in recent decades has focused on specific risk factors, such as second-hand smoke or radon, an odourless radioactive gas from traces of uranium in certain soils that can seep into basements in some regions. Population-health researchers determined that children living in lower-income neighbourhoods near highways tended to have elevated rates of asthma, likely because of tailpipe emissions. Yet such findings—which implicate urban-planning and social-equity policies—haven’t really translated into reform.
Certain building-specific IAQ issues—asbestos dust, for example—were identified, and strict remediation requirements were imposed when they cropped up in places like older schools or government offices. In other cases, such as mould contamination in damp basements or poorly constructed homes, building and health experts have long recognized the relationship between these conditions, which can be toxic, and inadequate ventilation coupled with excess humidity. To contain the spread of spores, mould remediation is necessary, but this exacting work remains largely the responsibility of the dwelling owner. The City of Toronto, for example, has a mould management policy, but it applies only to city-owned buildings.
The most consequential event, when it comes to IAQ and infectious diseases, occurred in 1976 at a Philadelphia hotel, where scores of American Legion members attending a conference fell ill. Twenty-nine subsequently died from a severe form of pneumonia. Investigations revealed that a deadly bacterium, dubbed legionella, had formed in the hotel’s air conditioning system and spread on airborne water droplets that were inhaled. Legionnaires’ disease continues to affect thousands of people each year. It is on the rise in the US and Europe but is relatively uncommon in Canada.
Two years after that outbreak, building scientists from around the world gathered for the first ever annual IAQ conference, held in Copenhagen. The timing was intentional. After the 1974 OPEC oil embargo, energy costs skyrocketed, forcing property managers and developers to look for ways to reduce the energy consumption of their buildings. This shift inspired a generation of architecture that featured hermetically sealed buildings, designed to prevent heat loss and thus keep energy costs low. In high-rises, windows either couldn’t be opened or were tiny apertures. The occupants had to trust that the building’s mechanical systems would provide adequate ventilation.
The design of the systems, though, didn’t work. In fact, the shift ushered in an era of so-called sick-building syndrome—produced by crowded structures filled with stale, recirculated air and the off-gassing of volatile organic compounds, including formaldehyde, from synthetic building products. This was a turning point, according to Cara Sloat, a Toronto-based mechanical engineer and one of Canada’s leading designers of ventilation systems. She is also an active member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the organization that sets global standards for most HVAC systems, and she has been outspoken about the importance of leveraging building science to fight the pandemic. “I’ve never sat in a lecture where I didn’t feel sleepy,” she says. It turns out she had been breathing in enough CO2 to affect her cognition. “It wasn’t that I was bored.”
Melanie Kiechle points out that female office workers were among the first to call attention to the phenomenon of indoor environments being difficult to concentrate in. She adds that women, in their much earlier traditional roles as managers of domestic spaces, played a critical role in identifying and trying to prevent unhealthy indoor air. In the 1980s, developers and property managers facing mounting complaints from tenants and office workers had to invent fixes to cure sick buildings. These solutions, which ranged from improved ventilation systems to windows that could open, sparked a renewed respect among some architects for a design concept that goes all the way back to ancient Egypt: cross ventilation.
While media and expert attention on sick-building syndrome did serve as a wake-up call, sick buildings did not make their occupants truly ill, and so regulations for ventilation remained minimal and generally not well enforced. Sloat says she has a colleague at ASHRAE who often begins PowerPoint presentations about “acceptable indoor air quality” with a pointed reminder. “She puts the title up and zooms in on it and says, ‘Not good, not great, not outstanding. Acceptable air quality.’ What we mean by that is essentially air that no one objects to, which does not have any objectionable odours, and is not full of too much CO2.”
As it turns out, SARS-CoV-2 had no trouble navigating through the merely acceptable indoor air that exists in many of our larger buildings. Furness says there have been various super-spreader events—such as the choir rehearsal near Seattle in March 2020, for example—that can’t be explained just in terms of proximity. The fact that they took place indoors was also key. A Korean research team published a paper pointing to airborne transmission in a Seoul apartment building where, in 2020, the virus infected the occupants of two columns of units, each connected vertically through a single bathroom ventilation duct. “This study suggests aerosol transmission, particularly indoors with insufficient ventilation, which is underappreciated,” the authors concluded. Other academic studies have offered similar findings, including from long-term care facilities where dozens died from aerosol transmission of the virus.
ASHRAE also weighed in by stressing the importance of IAQ as an infection-prevention tool that was available to public health officials: “Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air.”
The wrinkle, however, was in finding the evidence of airborne transmission that met the test of medical science applied by powerful public health agencies like the CDC and WHO. One way is to swab “no touch” surfaces, like the tops of door jambs or bookshelves, to test for the virus’s RNA. Another is air sampling: “There are now dozens of studies that have found the virus in the air in both community and health care environments,” says Jeffrey Siegel, a University of Toronto professor of civil engineering who has participated in some of these projects. Siegel, who notes that sometimes the sampling technologies either can’t detect the virus or can inadvertently destroy traces, says that air sampling can be a challenge. “Just because we find the RNA does not mean there is the ability to cause infection. But it might have at some point in its life cycle.” Viruses are fragile, he adds. “After a few hours on a typical surface, it’s not going to have the ability to cause infection.” His broader point is that nascent testing technologies will evolve and become more precise, as has been the case with earlier generations of such devices.
Well away from the academic debates playing out in journals and public health agencies, some people were uncomfortable with the inadequacy of the standard precautions—including masks, physical distancing, plexiglass partitions, and the like—that were emanating from government officials tasked with steering the COVID-19 response. (The antimasking/antilockdown/antivaccine voices that marched, protested, and tweeted tended to get a lot more media and political attention.) Tracy Casavant, a Vancouver resident with an engineering degree and a compromised immune system, became deeply concerned with the ventilation systems in her kids’ school. She tried to get the board of education to provide her with certified professional assurances, like an engineer’s opinion, that the school had been refurbished with high-grade filters and ventilation systems that increased circulation to ensure that the air in the classrooms was being changed frequently. Given her own condition, Casavant had no choice but to place severe restrictions on her children’s attendance, such as telling them not to eat lunch indoors at school or participate in some extracurricular activities. She faced resistance from the school’s board, its trustees, and also BC’s public health officials. “It quickly became apparent that it wasn’t that they weren’t aware of the science,” she says. “You can’t ‘individual responsibility’ your way out of an airborne pandemic.”
About three kilometres northwest of Rebecca Towers in Hamilton sits another tower of similar vintage, on a slight promontory overlooking the city’s postindustrialized harbourfront. For years, the Ken Soble Tower, an eighteen-storey structure owned and operated by CityHousing Hamilton, was home to so-called hard-to-house tenants, mostly men and largely unemployed. In 2015, the agency announced it would empty the fifty-year-old building and undertake long-overdue repairs as part of a broader overhaul of its assets, including a transformation of the tower into a low-income seniors’ residence.
When Ken Soble reopened in late 2021, it had undergone one of the most extensive “passive house” retrofits ever completed in Canada. Passive house is a European approach to energy efficiency that involves ultrathick insulation, minimal gaps and leaks in the exterior walls, and the recovery of all forms of waste heat energy, from sources like exhaust fans, drains, and appliances. Such buildings can reduce their energy consumption by as much as 90 percent compared with similar structures and are well known for having very fresh air because they require extensive ventilation. The renovation, led by Toronto-based ERA Architects, with Sloat as a principal consultant, was conceived prior to the pandemic, but the building now stands as an example of how to create safe apartment buildings with exceptionally high IAQ.
Sean Botham, the agency’s development manager, says the 146-unit tower offers deeply or modestly affordable apartments, most of them one bedroom. The faint hum of ventilation fans is noticeable, but so is the crispness of the air inside, evidence of the high rate of air changes per hour prescribed by passive house design. “We blew past these very rigorous standards,” he says.
Passive house design, though widely used in Europe, is still relatively new in Canada. Botham first heard of this approach at the 2010 Vancouver Olympics, where one of the pavilions had been built to passive house standards. A few years later, knowing that CityHousing was planning a major renovation of the Ken Soble Tower, Botham proposed the approach to the agency’s then CEO, Tom Hunter, who had a health care background. “He had this focus on how do we actually improve well-being and health,” Botham says, “and so he latched on to this idea when I pitched it—not just energy performance but it’s occupant health and well-being that are improved by better-quality air.”
Recent research from Harvard has shown how office workers fared on tests in rooms with typical ventilation, improved ventilation, and the best ventilation. The results in controlled rooms were spectacular, showing 60 to 100 percent improvements for the tasks carried out in well-ventilated spaces. Even before the pandemic, Joseph Allen, who heads the healthy-buildings division at Harvard’s school of public health, was something of a ventilation evangelist, expounding on how employers and educational institutions can significantly improve productivity, profitability, and academic performance with relatively modest investments in ventilation and high-performance filters. With COVID-19, he’s doubled down on his argument. “One of our biggest frustrations over the past year is that we knew enough to act early on,” Allen told Science. “Even by late January 2020, we knew that airborne transmission of aerosols was not only likely but probable.”
At the Ken Soble Tower, the building’s new mechanical system, designed by Sloat, draws air in, conditions (heats or cools) the air, and then pumps it down into the building. What’s different from traditional apartments, though, is that incoming air is shunted through large ducts from that rooftop intake directly into each unit; shared air is not forced through corridors or other communal spaces. Inside the apartment, there are exhaust fans in the bathroom and over the stove. The air travels only in one direction. “It’s a single-pass system,” Sloat says. “When [the air] goes out, it never goes back into another space again.”
Inside the apartment units, the hefty European-style triple-pane windows open and close, but the seals are so tight there are no drafts. Tenants can control the temperature in their own units with a digital thermostat. There’s no AC, but the ventilation system is designed to bring the indoor air temperature down to twenty-six degrees on the hottest days. As the passive house design promises, the air in the unit is fresh, cool, and odourless. It’s as if a window had been left open on a pleasant day.
In 2017, a fire raged through Grenfell Tower in London, UK, killing seventy-two people. In that case, the cause had to do with inadequate fire-proofing on the exterior cladding, but it drove home the realization that poor building design can be deadly. It was a wake-up call for Graeme Stewart, one of the two lead architects on the Ken Soble project, but also a lesson that ventilation experts like Jeffrey Siegel and some epidemiologists like Colin Furness have been arguing for during the pandemic: long-ignored failings in the ventilation systems in our homes and workplaces can become vectors of contagion during infectious-disease outbreaks. In short, building science matters.
How that science is applied, though, remains a work in progress. Take water and wastewater systems in our buildings and cities, for instance. The regulatory environments of both systems today are founded on principles of germ theory and hygiene that may have once been contentious but are now settled science. If you hired a contractor to renovate your bathroom and insisted that it would be fine to draw tap water from the toilet bowl, you’d be met with incredulity. A dense thicket of regulation, building-code practice, and professional standards would prevent such a move, and the insights behind such defences go back to nineteenth-century discoveries about contaminated water.
Air, though, has been different. As the pandemic has shown and contemporary public health experts have only grudgingly conceded, the air in buildings can be as deadly as contaminated tap water. But, despite mounting evidence from places like Rebecca Towers, IAQ remains subject to minimal standards, outdated infrastructure, inadequate regulation, and the discretion of developers and property managers—some of whom care and others who don’t.
Unsurprisingly, public expectations about clean indoor air have shifted in the past three years, and these now express themselves in the surging multibillion-dollar market for various air-quality devices, from portable CO2 monitors to ionizers, UV filters, humidifiers, and essential-oil diffusers. Some developers are now promoting the “wellness” elements of their condos, and at least two building-certification systems—Fitwell and WELL—have emerged alongside more traditional green-building seals, like LEED, with either implicit or explicit promises of air that won’t kill you. In Boston, the board of education has installed CO2 monitors in every classroom and created a web platform that allows parents to check the levels online in real time. (Increased CO2 levels are a bit like the proverbial canary in the coal mine.)
However, all the air-quality experts I interviewed counselled extreme caution with many of these consumer gadgets, most of which Siegel dismisses as the air-quality equivalent of patent medicines—or worse. “I estimate about 50 to 75 percent of the air-cleaning businesses is questionable at best and bogus at worst,” he says. “It’s a real problem, and it’s not a new problem.”
Access to high-quality indoor air can be seen as something of a social dividing line, Siegel notes, with lower-income or marginalized communities far more vulnerable to conditions such as recycled apartment air that is more likely to contain virulent aerosols than the air in private homes or luxury condo apartments. Without question, what we’ve learned about IAQ—from technical, economic, and social perspectives—points directly toward a new era of public health regulations along the lines of those sparked by air- and water-quality crises in the nineteenth and twentieth centuries.
Imagine, for instance, if all multiunit residential buildings—as well as factories, offices, retailers, theatres, gyms—should have to post an “indoor air quality certificate” at their entrances, modelled on the green-yellow-red rating signs that restaurants in many cities must now display to show whether their premises meet hygiene standards. An IAQ rating, assigned by building inspectors on a regular basis, could indicate whether the building’s ventilation system is providing continually refreshed air drawn from the outside and passed through a high-grade HEPA filter.
Even without prohibitively expensive retrofits, such as the one at the Ken Soble Tower, it’s possible to make significant upgrades. “The cost of improving indoor air quality is tiny compared to the benefits,” says Siegel, citing research showing $10 to $100 returns for each dollar invested, as compared with the incalculable expense associated with neglecting something we all need. “We are leaving money on the table by not addressing IAQ.” But, as with fire-safety and other building-code requirements, these choices should no longer be left mainly to the discretion of the landlord or property manager.
“COVID has gotten steadily more contagious, which has caused the air quality drumbeat to grow louder,” observes Furness. “But it still isn’t loud enough for most people, let alone employers, etc., to internalize. I have yet to see a hotel advertise its air quality.” He argues that the COVID-19 pandemic must be seen as a call to action for society to confront an invisible problem that has been neglected for decades. We’ve arrived, he observes, at a “Semmelweis moment,” which is to say an inflection point in our understanding of infection and prevention. After decades of ignoring the risks that lurk in the ventilation systems tucked in the walls of our homes, apartments, or workplaces, the lesson of the pandemic is that we need, as a society, to understand that the quality of indoor air demands the kind of political attention that has been focused on eradicating the pollutants in outdoor air since the 1970s. “Four years ago, if you and I were talking about building air quality, we would be putting each other to sleep,” Furness says. Now we have the opportunity to rethink the air we breathe.