School air monitoring: A win for public health

Air quality monitors in classrooms can make schools safer and demonstrate effectiveness of HVAC investments.

Clean air

COVID-19 taught many Americans critical lessons about the importance of indoor air quality – including in our schools.  

The arrival of COVID-19 saw many schools ill-equipped to consistently deliver clean, virus-free air to students, teachers and staff. According to a 2014 U.S. Department of Education report, 30% of surveyed public schools reported HVAC systems in “poor or fair condition.” In June 2020, just a few months after the COVID-19 pandemic began, the Government Accountability Office (GAO) found that 41% of surveyed school districts needed HVAC system upgrades or replacements in more than half of their schools.

COVID-19 isn’t the only airborne threat to student health; other pathogens, such as influenza and RSV, have also disrupted learning, causing outbreaks of illness and prompting school closures. To make matters worse, waves of wildfire smoke in the last few years, especially in the American West, have posed an elevated health risk to younger students and those with asthma or other breathing problems

Not only does poor ventilation have the potential to harm students’ health, but many parents also lack the ability to determine whether their school is doing a good job providing healthy air to their children.

Boston Public Schools (BPS) provides a vision of how students can have healthier air and parents can be better informed about school indoor air quality. In the last few years, BPS has installed HEPA air purifiers in every classroom, performed thousands of HVAC filter upgrades and added an indoor air quality sensor in every classroom to enable real-time monitoring and timely resolution of indoor air issues. This approach could be worth considering elsewhere as schools across the country continue working to improve indoor air quality.

What are schools doing to improve indoor air quality?

Many school districts have made indoor air quality improvements since the beginning of the COVID-19 pandemic, but significant gaps remain, according to a Centers for Disease Control and Prevention (CDC) survey of U.S. school districts in late 2022. The survey asked about several indoor air quality improvements.

  • 33.9% of school districts reported that HVAC upgrades had been made or were in progress in at least half of their K-12 schools. 
  • 28% reported that HEPA filters had been installed or installation was in progress in classrooms and/or cafeterias in at least half of their K-12 schools.

How does school indoor air monitoring work?

BPS is among those school districts that have invested in improving indoor air quality during the COVID-19 pandemic. But BPS has taken the additional step of monitoring the impact of those improvements on indoor air quality and sharing that information with the public. 

The indoor air quality sensor installed in each BPS classroom continuously measures four different pollutants, along with temperature and humidity. Parents can view minute-by-minute indoor air quality data across the district on an online dashboard and find information about their student’s school and classroom. The dashboard also offers the option to download the last 30 days of data, so anyone interested can get a better long-term idea of indoor air quality for the school district as a whole or a particular school or classroom.[1]

Imagine, for example, that you are a parent of a student at the Eliot Intermediate School, located in Boston’s North End. The BPS indoor air quality dashboard provides a readout of how air pollution levels in each classroom vary hour-by-hour and day-by-day. 

We examined the average pollutant concentrations on school days (between 6 a.m. and 6 p.m.) in every room at the Eliot Intermediate School for which data was available between September 7 and October 7, 2023. Of the 547 “room-days” for which data were available, 96.9% had an average carbon dioxide concentration below 800 parts per million (ppm), the CDC’s benchmark for good ventilation.[2] Carbon dioxide is a common indicator of ventilation quality because exhaled carbon dioxide (and other airborne contaminants like viruses) will gradually accumulate in poorly ventilated spaces, potentially putting occupants at risk. With the caveat that daily averages can mask hourly variation in carbon dioxide levels, these readings would give you as a parent confidence that your student’s classroom was well-ventilated. 

The BPS air monitoring data would also provide you with insight into the effectiveness of air filtration in your student’s classroom. Filtration involves mechanically removing allergens, viruses and other contaminants from the air. Filtration may be performed by an HVAC system and/or a free-standing device like a HEPA purifier, and it is especially important when the outdoor air being vented into space is of lower quality. 

For example, wildfire smoke worsened outdoor air quality in much of the country in the summer of 2023, making it less safe to use windows for ventilation. According to the Environmental Protection Agency, fine particulate matter which includes soot, airborne chemicals and other particles suspended in the air is theair pollutant of greatest public health concernfrom wildfire smoke. Short-term exposure has been linked to asthma attacks, bronchitis and other respiratory issues, while long-term exposure is associated with “reduced lung function growth” in children and premature death for people with heart or lung diseases.

HEPA air purifiers have been shown to significantly reduce the airborne concentration of fine particulates and appear to have helped at the Eliot Intermediate School. Based on data from the school’s roof sensor, on school days from September 7 to October 7, 2023, the average daily fine particulate level within the school was 36% lower than the average daily fine particulate level in the air directly outside.

Eliot Intermediate School students, teachers and staff appear to be very well protected from fine particulate matter overall, with 99.8% of daily room averages over school days in the same month-long time frame below the EPA’s health-based 24-hour exposure standard of 35 micrograms per cubic meter. 

How can parents, students and administrators use indoor air quality data?

It’s not hard to imagine how such detailed data on indoor air quality would be useful to administrators and parents. School administrators can use the data to evaluate the effectiveness of the HVAC investments they have made and prioritize improvements in classrooms that fail to meet health standards. Teachers, parents and staff can use the information to evaluate how indoor air quality may be affecting their health and that of students, and perhaps to manage their own exposure to indoor air pollution.

What opportunities are there for schools to monitor and improve indoor air quality?

The federal government appropriated $190 billion of Elementary and Secondary School Emergency Relief (ESSER) funds for state and local education agencies to mitigate the wide-ranging effects of COVID-19 on students and schools, including through improved indoor air infrastructure. As of August 31, 2023, all states still had at least 15% of their share of this funding left to spend, which means hundreds of millions or even billions of dollars are potentially available for such enhancements in each state. For example, Massachusetts had spent 54% of its ESSER funds through the end of August 2023, so it has more than 1.3 billion dollars left to allocate before the September 30, 2024 deadline. With COVID-19, other viruses, wildfire smoke and other forms of pollution continuing to threaten students, teachers and staff, school districts should prioritize investments in monitoring and improving indoor air quality. 

Boston Public Schools shows that such an approach can pay real dividends for public health, and create better-informed school communities.


[1] To download the last 30 days of data for the district as a whole, click the three-line symbol in the upper right-hand corner of the dashboard home page, click “District Summary Report,” go to the “Latest Sensor Results” tab, and click “Export to Excel.” 

To download the last 30 days of data for a particular school, navigate to the school, click the “30 Day Report” tab, and click “Excel.” 

[2] Data was downloaded from the BPS Indoor Air Quality Dashboard on October 11, 2023. The carbon dioxide concentration figure includes all indoor sensors for all school days on which the sensor recorded a value.


Louis Sokolow

Former Policy Associate, Frontier Group

Andre Delattre

Senior Vice President and Chief Operating Officer, Program, The Public Interest Network

Andre directs The Public Interest Network's national campaign staff and programs. His previous roles include national organizing director of the Student PIRGs and executive director of PIRG. He also serves on the executive committee of the Financial Accountability and Corporate Transparency (FACT) Coalition. He lives in Chicago with his wife and daughter, and is an avid cyclist and chess player.