The New York City public schools that rely solely on open windows and portable air purifiers have seen 23% more COVID-19 cases per students and a 29% increase in staff case rates when compared to buildings with stronger ventilation, such as HVAC systems, according to a new WNYC/Gothamist investigation.

The findings raise new concerns about the adequacy of dozens of public schools as winter approaches and schools struggle to deal with aging buildings amid the pandemic. The data also suggests that school officials purchased inadequate air purifiers and are over relying on them to help combat the airborne virus -- an issue raised in a previous WNYC/Gothamist investigation.

Starting in summer 2020, the city purchased two air purifiers for every classroom from a Manhattan-based startup named Delos Living and its upstate partner Intellipure — a choice officials strongly backed ahead of the school year, even though the devices lack HEPA filters, the industry benchmark for air cleaning.

In interviews with WNYC/Gothamist, independent engineers warned of relying too heavily on the Intellipure purifiers and open windows, which city officials countered were adequate in reducing the risk of COVID-19 spread.

To learn why Intellipure air purifiers were selected for classrooms, WNYC/Gothamist has discovered that New York City’s Department of Education (DOE) got those devices for a bargain, according to contracts obtained via Freedom of Information requests.

The Intellipure Compact purifier and its replacement filters retail for $549 and $220 each. But the contracts show the city paid between $209 and $390 for the purifiers and as little as $53 for each filter. New York City used pandemic funds acquired from the Federal Emergency Management Agency (FEMA) to buy the air purifiers, according to the contracts.

The city has spent $58 million on the $64 million contracts so far, placing the devices in tens of thousands of classrooms. Those expenses paid for 157,000 Intellipure Compacts, 157,000 replacement filters and shipping costs.

Public documents also show Delos Living launched a lobbying campaign in the summer 2020, as the city made preparations for its first full school year under COVID-19. The effort targeted a broad set of senior officials — from Mayor Bill de Blasio’s administration to borough presidents and councilmembers.

Delos Living is headquartered in Manhattan's Meatpacking District.

Kasirer, a Tribeca-based lobbying firm with ties to the de Blasio administration, earned $195,000 for the project between July 2020 and August of this year, the month before classes resumed. Records show this firm led New York City lobbyists in compensation in 2020 — earning about $14 million.

Yet despite the purchase of Intellipure air purifiers for schools, New Yorkers who walk into most city buildings are unlikely to find that brand of purifier humming in the background. City contracts and photos sent to WNYC/Gothamist by city employees across several departments indicate that most offices rely on other brands, all of which use HEPA filters and provide substantially higher ventilation rates compared to the purifiers in city schools. Some were purchased even as the city made new deals with Delos for non-HEPA purifiers, the contracts show.

The mayor’s office, for example, purchased ENVIRCO IsoClean 800 purifiers in April 2021 that were delivered to 253 Broadway, a building across from City Hall that houses multiple divisions of the mayor’s office. A ventilation expert calculated that this model offers five times as much airflow per hour as the Intellipure Compact air purifiers in the city’s classrooms. The city signed two new contracts for Intellipure air purifiers the same month.

Spokespeople for the mayor's office and education department said 30 different devices were considered for classrooms. They did not answer repeated questions about whether a competitive bidding process was undertaken, but City Comptroller’s records show only one vendor was contacted to bid on each contract. They said Delos and two intermediaries based in the city — MCT ProTools and K&S Industrial — were chosen to provide Intellipure air purifiers because of their competitive cost and overall device effectiveness and efficiency.

But building engineers said the Intellipure model does not offer sufficient ventilation on its own in an average-sized classroom, even when placed on its maximum setting.

If they're not moving a lot of air, then that limits how much air cleaning they can really do.
Dr. Brent Stephens, Illinois Institute of Technology

“If they're not moving a lot of air, then that limits how much air cleaning they can really do,” said Dr. Brent Stephens, who leads the Illinois Institute of Technology’s Built Environment Research Group. Earlier this year, he and his team assessed the Intellipure Compact and found that it ranked ninth out of 12 products they’ve tested in terms of performance.

Several competitors also make air purifiers that are similar in size to the Intellipure Compact, but are cheaper, offer better clear-air delivery rates and are quieter for use in classrooms.

New York City teachers told WNYC/Gothamist that they often run their Intellipure air purifiers below the maximum setting because of the noise they cause. Many said the city’s Department of Education had not provided specific instructions on how high to run the purifiers. In one school, teachers are instructed to leave their air purifiers on low.

The DOE said educators with questions about the purifiers should speak with their school’s custodial engineer.

“I often move the air filters around so that they’re not right next to a window or a wall,” said a Brooklyn teacher who asked not to be identified by name due to fears of retribution. “We have received no guidance on how to place them and the speeds to put them on — I learned how to do this by following other teachers on Twitter.”

At one New York City school, custodial engineers posted signs advising that air purifiers remain on low.

One of the teacher’s own children attends a school that relies only on open windows and air purifiers, and the child has reported feeling consistently cold in the classrooms.

“I confirmed with my son that the windows are open in the classroom,” the teacher said this week. “In fact, this afternoon, the teachers sent an email reminding families to send kids with appropriate layers — coats, hats, scarves, gloves.”

In an emailed statement, Nathaniel Styer, a Department of Education spokesperson, said that schools with natural ventilation are designed with heating systems to compensate for open windows.

“As we did last year, we will work with custodians and principals to ensure every classroom is operating at the appropriate room temperature,” he said.

But as winter approaches, temperatures will become more unpleasant and people will be spending more time indoors, where the coronavirus thrives. Temperatures this week are already slipping into the 40s and it could snow this weekend. Infection rates are again rising in New York City, and children ages 5 to 11 have led weekly case rates since schools opened in September.

The windows-only buildings identified by WNYC/Gothamist as having higher COVID-19 case rates represent a small portion of the nation’s largest school system — 61 of the city’s 1,250 buildings with readily available ventilation reports. But these buildings still serve 28,300 students and employ 4,600 staff.

Public health experts say the findings are a reminder of the ongoing risks of the pandemic. COVID-19 has preyed upon the blindspots in our health infrastructure — including indoor areas that are poorly ventilated. Even as safe and effective vaccines are provided for younger children, there is still value in clean air.

“The co-benefits of having good ventilation are undeniable, right? There are plenty of studies that show that in a space with poor ventilation, the test scores are lower,” said Dr. V. Faye McNeil, a professor at Columbia University and an aerosol scientist. “Ventilation is always important if we're sharing indoor spaces, especially in a school.”

How We Performed This Analysis

The New York City public school system provides ventilation data for 58,500 classrooms, most of which are in use. A vast majority of those classrooms — 92% — are connected to mechanical ventilation such as window exhaust fans and heating, ventilation, and air conditioning (HVAC) systems. But this still leaves approximately 4,800 classrooms spread across 615 buildings where the only way to circulate air is to open the windows.

The city’s Department of Education does not publicly release figures on the total number of COVID-19 cases identified among students and teachers in each school, making it difficult to track the size of outbreaks in individual buildings.

To reveal these trends, WNYC/Gothamist used COVID-19 case data that city officials are required to deliver daily to the New York State Department of Health. (Parents can find this data via the state’s COVID-19 report card.)

Our team then matched those case records from NYC school facilities against building surveys collected by the city’s education department — which provide classroom-by-classroom details on ventilation infrastructure.

For this analysis, WNYC/Gothamist defined “low-ventilation” school buildings as those where 90% or more of their classrooms depend solely on windows and the two Intellipure purifiers for air circulation.

These were then compared to “high-ventilation” school buildings in the same zip code — ones where 90% or more of classrooms have access to exhaust fans and HVAC systems.

Comparing schools within the same geographic location helps account for various factors that might influence COVID rates among students and staff, such as community transmission, income level, access to health care, attitudes toward wearing masks and vaccine hesitancy.

Not only were there 23% more COVID-19 cases among students in low-ventilation buildings between the start of the school year and the end of October, the WNYC/Gothamist analysis also found student cases were 37% higher after the first three weeks of classes. Independent experts at the American Statistical Association and the City University of New York reviewed the analysis and agreed with its approach and main takeaways.

“This analysis is helpful because it's a reminder that the spread of infectious diseases depends on multiple things,” said Bruce Y. Lee, a public health policy expert at CUNY and executive director of Public Health Informatics, Computational, and Operations Research. “A lot of the variation when it comes to resources and types of neighborhoods can be separated out when it comes down to the zip code level.”

But he added that other variables could explain the COVID trends. Older schools could have worse ventilation because of more basement classrooms or be less likely to have HVAC systems. Or those campuses could have cramped layouts and tight hallways that may not be conducive to social distancing, he said.

The high-ventilation and low-ventilation schools have similar person-to-classroom ratios, about 18 to 20 students and staff per room on average. That suggests population density isn’t behind the difference in COVID rates. The low-ventilation schools in the analysis have an average opening date of 1936 — 24 years older than the high-ventilation schools in the same zip code. But 19 out of the 61 low-ventilation schools are newer, having opened since 1990.

Success Academy Charter School-Washington Heights ranked among the top-15 low-ventilation schools, both in student and staff case rates.

Sorting the data by school type shows the effect of poorer ventilation on case rates is most pronounced among elementary schools. Kids ages 5-11 were ineligible for COVID-19 vaccines through October 29th. Elementaries were also the most common type of school among those with low-ventilation, accounting for 70% of them.

Lee from CUNY said comparing schools within census tracts, which are smaller in geographic size than zip codes, could further help to pinpoint what role ventilation plays in varying infection rates. At that geographic level, staff cases were 46% more common in low-ventilation schools, while student cases were 17% higher.

Styer claimed the WNYC/Gothamist analysis is inaccurate because it ignores “the fact that many of our students attend schools outside the zip codes they reside in.” Yet many New York City students do not participate in the school choice program. The city’s Independent Budget Office reported in 2017 that only 29% — less than a third — of K-5 students attend school outside their assigned zone. In some districts, as few as 2% of these students travel out of their zone.

The city said that infections at the low-ventilation school buildings only account for 2% of verified cases at public schools. But focusing on the total number of cases — rather than the rate — obscures the risks connected to particular settings and variables like classroom density.

“It is clear our schools are safe – with well-ventilated classrooms, a universal staff vaccination mandate, a miniscule positivity rate of 0.24%, and next to no school closures,” said Styer from the education department.

School closures have risen recently — only one had been reported prior to November when two closures happened in a single week. And because parents and kids can opt-out of the education department’s COVID testing program, it only monitors about a third of the city’s students. This group is self-selected and may not reflect true transmission among children. Along those lines, the latest positivity rate for city kids ages 5-17 averages around 1.16%, according to city data. That citywide rate is five times higher than what’s being measured by the education department’s separate testing program.

“The design of the indoors can actually affect your health as well. This is uncovering more issues that really need to be addressed,” Lee said.

How To Compare Purifiers

When shopping for indoor portable purifiers, ventilation experts say people need to focus on two attributes: filters and airflow.

HEPA filters have been a standard bearer since the 1940s — when the U.S. Department of Energy developed the technology to prevent radiation poisoning.

“They actually used to be classified military technology,” said Dr. William Bahnfleth, chair of the Epidemic Task Force at the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and an architectural engineering professor at Pennsylvania State University. “They were developed for the Manhattan Project to keep people from inhaling particles that were radioactive.”

A HEPA filter is generally made from glass fibers, and in the United States, it must be at least 99.97% efficient at capturing smoke — or other particles about 0.3 micrometers in size. Multiple studies published during the pandemic — including one this summer by the Centers for Disease Control and Prevention — show portable HEPA air cleaners can reduce exposure to simulated airborne particles by 65%.

The Intellipure Compact air purifier — sold to New York City schools — carries a proprietary filtering system that the manufacturers claim matches or surpasses HEPA. The company’s technology relies in part on electrostatic precipitation, meaning it uses static electricity to scrub particles from the air.

“It's like lint sticking to your clothes,” Bahnfleth said.

The biggest concern with air cleaners claiming ‘HEPA-equivalent’ performance is how they perform over time.
The CDC

In response to questions submitted by WNYC/Gothamist, a team of researchers at the CDC with expertise in air filtration questioned the city’s decision to rely on purifiers that don’t use HEPA filters.

“As a true HEPA filter loads with particles over time, the overall filtration efficiency will only increase,” meaning the more it’s used, the better it is at cleaning the air, the CDC said. “The biggest concern with air cleaners claiming ‘HEPA-equivalent’ performance is how they perform over time.”

A Delos spokesperson said its filters would also improve in efficiency as dust builds up. But while the air exhausted from HEPA purifiers can be assumed to be particle-free, the CDC researchers said the same cannot be said for electrostatic precipitators.

“They can be extremely efficient at removing particles from a moving airstream,” the CDC said. “However, as electrostatic precipitators capture particles and become covered in a layer of dust, the efficiency decreases. It is unclear how efficient the overall air cleaner will be when this happens.”

The CDC said the potential downsides explain why its guidelines call for school officials and building managers to clearly state when they’re using a non-HEPA purifier to fight COVID-19. The CDC recommends schools consider using portable air cleaners that use HEPA filters “to enhance air cleaning wherever possible.”

Another concern in evaluating the effectiveness of portable purifiers is airflow. The Intellipure Compact model doesn’t remove particles in the air as fast as its competitors. If a portable purifier isn’t pulling a lot of air through its fans and innerworkings, then the strength of its filter becomes inconsequential.

Stephens from the Illinois Institute of Technology offered a sheet of plywood as an example. It would technically block 100% of particles: “It's a perfect filter. But you can't move any air through it. So it doesn't do anything.”

When it comes to airflow, a purifier is measured by its clean air delivery rate, or CADR, which depends on the physical size of an indoor space. Take a classroom that’s 500 square feet with an 8-foot ceiling. To effectively remove hazardous particles, the U.S. Environmental Protection Agency and CDC recommend a purifier with a minimum clean air delivery rate of 325 cubic feet per minute (cfm).

The Intellipure Compact cleans the air at 150 cfm at its highest setting, meaning even the two Intellipure air purifiers currently allocated for each NYC school classroom would only offer 300 cfm combined. That’s below the standard recommended by the EPA and CDC.

“If you have an air cleaner in a space, that's too puny in terms of the amount of air that it circulates, it's not going to have much impact on the whole room,” Bahnfleth said.

The pair of Intellipure would underperform relative to devices found in the mayor’s office and other city agencies. The city’s health department uses Austin Air Healthmate purifiers, which are nearly three times as powerful when it comes to airflow. The devices located in the mayor’s offices move air five times as fast.

Subtract shipping costs, and the city spent about $48 million on Intellipure Compact purifiers and filters. For the same price, it could have purchased 68,000 of the health department’s Austin Air purifiers — enough to cover every New York City classroom with 10,000 devices to spare.

How Intellipure Was Chosen For Classrooms

WNYC/Gothamist asked the mayor’s office, the Department of Education, Delos Living and city councilmembers to explain why Intellipure air purifiers were chosen for schools given these performance issues.

Delos Living calls itself a leader in building healthier offices and living spaces, stating that it aims “to bridge the gap between evidence-based science and everyday awareness to elevate physical, mental and social health as central values in the built world.”

Launched in 2009, the company is well connected. Its advisory board includes former U.S. Congress members, the former heads of federal agencies, representatives from major health care systems such as the Cleveland Clinic and a former CEO of the Bronx’s Montefiore Health System and actor Leonardo DiCaprio.

Delos Living has no records of lobbying in the years leading up to the pandemic, according to records kept by the Office of the City Clerk. But two vice presidents at Kasirer — the lobbying firm commissioned by Delos — served in Mayor de Blasio’s administration: Kara Hughes and Charles Aidinoff

Delos, like many companies, has conversations with public officials on topics relevant to the city.
A Delos spokesperson

“Delos, like many companies, has conversations with public officials on topics relevant to the city,” a spokesperson told WNYC/Gothamist. “And we strictly follow all government transparency and reporting requirements whenever we do so.”

After Delos hired Kasirer in July 2020, records show their lobbying focused on a wide range of officials including Brooklyn borough president and mayor-elect Eric Adams, Manhattan borough president Gale Brewer, and several city council members including health committee chair Mark Levine and Speaker Corey Johnson. Senior members of the de Blasio administration — including former and current New York City Schools Chancellors Richard Carranza and Meisha Porter — were also lobbied.

City spokespeople said that at no point did Chancellors Carranza, Porter, or senior members of the de Blasio Administration have any conversations with Delos representatives about the purchase of air purifiers. But they did not address questions about whether Delos advised the education department in general on how many purifiers to place in each classroom.

A spokesperson for Johnson said the city council has absolutely no role in deciding DOE contracts, and that he and his team did not meet with anyone to discuss Delos Living air purifiers. Other council members named in the lobbying documents — Cornegy, Chin, Cabrera and Levine — did not respond to requests for comment.

Eric Adams did not reply, but Manhattan borough president Brewer said she had no involvement with Delos.

“The Borough President has no role in school procurement and she has not met with the party in question,” Aries Dela Cruz, press secretary for the Manhattan Borough President, said via email.

When asked why several city agencies selected air purifiers with HEPA filters and better airflow performance, Danielle Filson, a spokesperson for the mayor, revealed that City Hall is using the Intellipure devices, too. But none of the contracts obtained by WNYC/Gothamist have found a record of the mayor’s office purchasing its own Intellipure air cleaners, suggesting it may be relying on the education department’s federally funded emergency stockpile. The city did not respond to questions on this point.

WNYC/Gothamist submitted records requests for Intellipure contracts to both the Department of Education and the Department of Citywide Administrative Services (DCAS). While DCAS was able to turn over copies of the contracts, the education department’s deputy records access officer, Milena Schatzle, said it was unable to provide the same documents until February of next year. Schatzle did not respond to a request for comment as to why the education department could not deliver the contracts sooner.

What To Do When Winter Is Coming

This situation is a tough reminder of how the pandemic reshaped society and its relationship with airborne infections. In the past, scientists considered germs to spread in an airborne manner only when the transmission was observed at a distance, said Dr. Richard Martinello, medical director of infection prevention at Yale-New Haven Hospital.

“With COVID, it's really challenged us to think a bit more in depth,” Martinello said. His hospital, for example, responded by installing air purifiers in admission rooms where suspected COVID patients land before their diagnosis “in order to create safer environments.”

But pricey air cleaners aren’t the only solution. A Corsi-Rosenthal box is a do-it-yourself version of an air purifier that’s become popular among teachers. It can be constructed with simple materials like duct tape and box fan for less than $200. The DIY devices don’t use 99-percent-efficient HEPA filters, but the box fans provide higher airflow so they can remove plenty of airborne particles.

“Corsi-Rosenthal boxes have merv-13 or merv-14 filters on them. Those filters have maybe 50% to 80% efficiency for the particles that we’re trying to collect,” said Bahnfleth of ASHRAE. “But it removes a lot of particles by processing a lot of air.”

And New York City classrooms need some options. The Brooklyn teacher whose child attends a low-ventilation school said administrators reminded parents this week that classrooms are very cold right now because the city’s ventilation policy requires them “to keep windows open at all times.”

“We have responded by buying more sweatshirts,” the teacher said. “[They were] remote last year, so we haven’t experienced a winter with classroom windows open yet.”

Christopher Werth contributed to reporting. To see the data behind this story and learn more about how we analyzed it, check out this GitHub repository.