When wildfire smoke began blanketing New York City in June, employees at Skidmore, Owings & Merrill, an architecture and design firm in Lower Manhattan, had a panoramic view of the unfolding crisis. From their desks, nearly 30 stories off the ground, they watched as the sky transformed from hazy, slate blue in the morning to dirty, dishwater gray at noon. By midafternoon, they were looking out on an otherworldly skyline.

“It was apocalyptic orange,” said Charles Harris, an architect at the firm.

But inside the office, cool air rippled from the vents running along the ceiling, and large screens reassured employees: “Indoor Air Quality is Very Good.”

The assessment was based on the readings of indoor air-quality sensors that were tracking the real-time levels of pollutants, including the fine particulate matter that makes wildfire smoke so hazardous. The sensors had been installed during the pandemic, but now they were proving their worth in the midst of a new air-quality emergency.

“We can say definitively to everybody that works here that ‘You’re safe to come into the office,’” said Chris Cooper, a design partner at the firm.

In the United States, there is little regulation of indoor air quality, and once a building is up and running, occupants typically have little insight into whether the air they are breathing is safe.

Indoor air-quality sensors make the invisible visible. Design and engineering firms, themselves among the early adopters, say the pandemic spurred interest in the technology from clients, who are using it to monitor air quality in real time, optimize energy use and attract Covid-cautious tenants and employees.

“I think a new notion emerged that occupants might want to know the data about indoor air quality,” said Gideon D’Arcangelo, a designer at Arup, a global design and engineering firm. “And we’re also at a point where the technology can make that information available.”

Still, getting the most out of the new technology would require addressing age-old obstacles to improving indoor air quality, including the nation’s aging infrastructure and lack of regulation. Interest could fade now that the emergency phase of the pandemic has ended, experts said.

And a sensor system is not a simple solution. “It’s a great tool,” Mr. Harris said. “But we’re still learning what to do with it.”

Pandemic precautions

Skidmore, Owings & Merrill, known as S.O.M., not only leases space in the skyscraper at 7 World Trade Center, but also designed the entire building after the original World Trade Center was destroyed in the Sept. 11 attacks. Because of that history, the architects prioritized health and safety, incorporating features such as extra-wide stairwells for emergency evacuations.

This focus on well-being extended to indoor air quality, and the firm, which began designing its own office in 2019, was already researching sensors when Covid-19 hit. “The pandemic accelerated so many of these conversations,” said Mr. Cooper, who led the design of the office.

The company installed a system that tracked particulate matter, volatile organic compounds and carbon dioxide, which was an especially important indicator during the pandemic. Because humans exhale carbon dioxide, levels of the gas can build up when people gather in indoor spaces. High carbon dioxide levels can be a sign that a space is insufficiently ventilated — and that if a person with Covid-19 is present, coronavirus particles might be accumulating, too.

When the new office opened in 2021, Amy Garlock, an architect at S.O.M., was nervous about returning. Whenever she got a cup of coffee, she checked the air-quality dashboard by the office pantry. “It was always good,” she said. “That made me feel better about the place that I was working in.” She added, “It’s nice to have evidence of invisible things.”

The sensors are linked to the ventilation system, which automatically responds when conditions change. “We get pings whenever there’s a party that’s, like, ‘Oh, your CO2 levels are peaking,’” said Ojiakor Obinani, an architect at S.O.M. who helped evaluate and select the air-quality monitoring platform. When that happens, the ventilation system kicks into a higher gear.

Whether the system prevented viral transmission during the pandemic is difficult to say. S.O.M. also established other precautions, including vaccine requirements and social-distancing protocols.

“I sneeze a lot less in this new office,” Ms. Garlock said. But she couldn’t be sure that was because of the air quality. “Maybe fewer people are coming in to work with colds,” she speculated.

But the company always viewed the system as a long-term investment with benefits beyond the pandemic. Studies suggest that good indoor air quality can alleviate symptoms of asthma, reduce absenteeism and even improve cognitive function.

There could be savings, too. The system allows S.O.M. to deliver fresh air when and where it is needed, rather than running the ventilation on high all the time, Mr. Obinani said. So although the system cost $150,000 to purchase and install, with $8,800 in annual maintenance costs, the company expects to save nearly $250,000 in energy costs over the next decade, a 25 percent reduction.

The system would also help the company respond to whatever air-quality crises could loom in the future, even if they have nothing to do with infectious disease.

World on fire

As smoke drifted into the city on June 6, S.O.M. kept a close eye on the sensor readings. During the day, the ventilation system pulled the smoky air through high-quality filters, which trapped pollutants and kept the indoor particulate matter readings low.

Still, there was a palpable anxiety in the office the next day, when conditions outside worsened, Mr. Cooper said. Employees gathered by the windows, watching the darkening sky, and clustered around the sensor display screens, which raised no alarms about the office air.

“It felt comfortable inside,” Mr. Cooper said. “What was uncomfortable was looking outside.”

Around 3 p.m., there was a blip: One sensor detected rising levels of particulate matter. The team quickly determined the sensor was by the emergency stairwell, where the air smelled distinctly smoky. Polluted outdoor air was clearly infiltrating the stairwell, and the firm warned employees not to use the stairs.

The day played out differently at the company’s Washington, D.C., office. There, when the ventilation system ramped up, the level of indoor particulate matter rose. That suggested that the building might have been pulling in too much outdoor air or lacked filters good enough to trap the particulate matter.

When S.O.M. saw the air quality trending in the wrong direction, it notified the building manager, who changed the system settings to reduce the amount of polluted air it was drawing in from outside and instead recirculate more indoor air. “We could call attention to that and make a change,” Mr. Cooper said. The particulate matter levels dropped.

Sensing struggles

The pandemic prompted other companies to explore the use of sensors. The accounting firm Deloitte deployed air-quality monitors at international meetings in 2021 and 2022, in hopes of reassuring attendees nervous about the risk of contracting Covid.

Sterling Bay, a real estate firm in Chicago, expanded indoor air-quality monitoring to all of its properties and has been experimenting with using thermal sensors to monitor building occupancy. Buildings without these systems essentially “have blinders on,” said Patrick Biesty, the company’s managing director of engineering.

The approach has limitations. Carbon dioxide sensors, which do not measure levels of airborne pathogens directly, merely provide a rough proxy for infection risk. “There are many situations in which your transmission risk can be high, even when the CO2 levels are low,” said Angela Eykelbosh, an environmental health scientist at the National Collaborating Center for Environmental Health in Canada. For instance, a sky-high ventilation rate could keep the carbon dioxide levels low in a company cafeteria, but an office worker dining with an infected colleague might still become sick.

And it could be a challenge to put sensors into more buildings, especially because the interests of employers, workers and building owners do not always align.

“The people who pay the utility bill, the people who pay the salaries, the people who pay to build the building and so on aren’t the same institutions very often,” said Andrew Persily, an expert on indoor air quality at the National Institute of Standards and Technology. “If I’m a building owner, I’m being asked to put all this money into it. If the staff are more productive, they don’t work for me, I’m not going to benefit from that. Can I raise the rent? Well, that’s an interesting negotiation.”

Wider adoption would most likely require new standards, policies and incentives, such as mandatory air-quality inspections or tax credits for building owners who improve indoor air quality, experts said.

Moreover, they added, in many buildings, the underlying air-handling infrastructure — the fans and filters, dampers and ductwork — is poorly maintained, and improving indoor air quality will require investing in these basic technologies. Sensors are a “screening tool” for flagging when there might be a problem with indoor air, Dr. Eykelbosh said. “And then you do something else to improve the space.”

At S.O.M., the day after the sky turned orange, Mr. Cooper and Mr. Harris stood in front of one of the air-quality display screens, talking through the data. They puzzled over how smoke had gotten into the office overnight and why the air quality was uniquely bad in the stairwell. As architects, they viewed the office not just as their own workplace, but also as a laboratory.

“We’re trying to figure out what can we learn from this to keep ourselves safe right now,” Mr. Harris said, “but also for the future and to make better decisions when we design buildings.”