How indoor air quality in schools affects student learning and health

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The COVID-19 pandemic has forced a spotlight on indoor air quality in schools and the importance of proper ventilation.

It also has brought renewed attention to a longstanding problem in many U.S. classrooms: Air pollution, ranging from pet dander and paint fumes to mold, trace metals and formaldehyde.

For many years, schools facing funding shortfalls put off costly projects that would improve indoor air quality and ventilation — replacing roofs, for example, and updating their heating and air conditioning systems. When the federal government announced last year that it would distribute $123 billion in emergency relief funds to help schools prevent the spread of COVID-19 and recover from its impact, school districts had backlogs of deferred renovation and maintenance.

Education officials have a lot of flexibility in how they use that money, the bulk of which remains unspent, according to a recent Washington Post analysis. Public health leaders, researchers and advocacy organizations have urged them to put some of it toward improving indoor air quality.

“As government pandemic relief becomes available to schools, there is an unprecedented opportunity to address a decades-long neglect of school building infrastructure,” members of the Lancet COVID-19 Commission’s Task Force on Safe Work, Safe School, and Safe Travel write in a report released in April 2021.

The U.S. Centers for Disease Control and Prevention has stressed that improved ventilation is crucial in helping prevent COVID-19 in schools. The deadline for school districts to spend funding provided in the American Rescue Plan, signed into law in March 2021, is September 2024.

As news outlets scrutinize school spending and cover the progress of these projects, it’s important to understand the current condition of school buildings and Heating, Ventilation and Air Conditioning, or HVAC, systems. Journalists also need to know what the research says about indoor air quality in schools and how airborne pollutants can affect students’ health and cognitive development.

Children are especially susceptible to health problems linked to poor air quality.

“Exposure to various air pollutants in school buildings risks severe damage to pupils’ health since they inhale a larger volume of air corresponding to their body weights than do adults,” a group of 19 researchers write in an October 2022 paper, “Indoor Air Quality and Health in Schools: A Critical Review for Developing the Roadmap for the Future School Environment.”

To help inform journalists’ coverage, we’ve gathered and summarized academic studies and government reports that examine these issues in the U.S. and abroad.

Together, they suggest:

  • Tens of thousands of U.S. schools have been operating with faulty or outdated HVAC systems, and many schools lack air conditioning.
  • Poor indoor air quality and ventilation are common in schools across the planet.
  • Certain pollutants often are found in higher levels inside school buildings than in homes and commercial buildings.
  • Poor indoor air quality is linked to a variety of health problems, ranging from coughing and wheezing to more serious conditions such as asthma and cancer.
  • Breathing polluted air harms students’ academic performance. If students get sick, they miss school. Studies also show that poor classroom air quality reduces cognitive ability.
  • Remediation efforts are hampered by the fact there are “no generally accepted criteria for distinguishing a problematic level of dampness and mold, which adversely affects health, from a non-problematic level of dampness and mold,” one researcher writes.
  • Improvements in outdoor air quality over the years has helped boost student test scores, raising the possibility that cleaner air could help reduce historic differences in test scores between Black and white children.
  • Climate change has created new challenges for schools, considering some airborne pollutants are more prevalent in warmer climates. As temperatures rise, some schools in cooler regions of the country have installed air conditioning.

The condition of school facilities

An estimated 41% of U.S. school districts need to update or replace HVAC systems in at least half their schools, which means at least 36,000 public schools are operating with faulty or outdated HVAC systems, according to this report the U.S. Government Accountability Office prepared for Congress.

The report spotlights a range of problems common in public school buildings nationwide that can affect student learning, health and safety. The findings are based on a nationally representative survey of school districts conducted in late 2019 as well as in-person visits to 55 schools in six states — California, Florida, Maryland, Michigan, New Mexico and Rhode Island — from June to September 2019.

Some of the other big takeaways:

  • 27.7% of districts reported needing to repair or replace roofs in at least half their schools. Moisture from leaky roofs “can lead to the growth of mold, fungi, and bacteria; the release of volatile organic compounds; and the breakdown of building materials,” according to the National Institute for Occupational Safety and Health. “Moisture also provides a favorable environment for cockroaches, rodents, and dust mites.”
  • 8.9% need to address “environmental conditions” such as mold, lead or asbestos in at least half their schools.
  • 20.6% of districts need to update or replace systems for monitoring indoor air quality in at least half their schools.

Site visits revealed that schools in cooler areas of the country have had to alter class schedules or install air conditioning systems as climates have warmed.

“Officials in a Michigan [school] district said about 60 percent of their schools do not have air conditioning, and in 2019, some temporarily adjusted schedules due to extreme heat,” according to the report. “Officials in a Maryland district said the district retrofitted some schools with air conditioning, but did not update pipes and insulation serving the HVAC systems, which has caused moisture and condensation problems in these buildings. Officials were concerned the moisture and condensation could lead to air quality and mold problems, but said that to remedy these issues could cost over $1 million for each building.”

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How common is mold and other types of indoor air pollution?

Researchers analyzed dust samples collected from 32 schools in densely populated areas in the northeastern U.S. and found they contained several types of mold. They also discovered mold levels in classroom dust often exceeded levels of mold found in dust collected from local homes.

Researchers tested samples taken from a total of 114 classrooms and the bedrooms and living rooms of 33 homes from 2014 through 2018. They tested for 30 types of mold, 26 of which are associated with water damage and 10 of which are associated with outdoor sources.

When the researchers looked for links between mold levels and rates of asthma among schoolchildren living in the area, they found asthma was most common in schools with higher levels of outdoor mold — the kind found in soil and on leaf surfaces, for example.

“Therefore, the differences in the prevalence of asthma was not indicative of any significant differences in mold growth resulting from water-damage indoors but rather factors associated with the increased levels of molds from outside entering and accumulating in the schools,” the researchers write, adding that 30 of the 32 schools studied did not have air conditioning.

“In addition to AC, the frequency of window and door opening could also affect the levels of [outdoor] molds,” they write. “Cleaning frequency and thoroughness could also affect the build-up of [outdoor] molds inside schools.”

Indoor air quality and child health, student performance

Indoor air quality in schools “is characterized by a complex of contaminants,” including molds, bacteria, volatile organic compounds, particulate matter, and trace metals from road traffic, the researchers write. They note that several studies have found that levels of certain airborne pollutants were higher inside schools than in homes and commercial buildings.

“Inhalation exposure to air pollution has increased children’s mortality rate, acute respiratory disease, and asthma,” they write. “Due to different responses of the children’s immune systems to indoor air exposures, various chronic diseases and symptoms have been reported and characterized as ‘sick building syndrome.’”

This paper is based on a review of 304 reports and research papers published between 1970 and 2022. It offers a broad overview of research examining types of pollutants. It finds, for example, that volatile organic compounds — a group of chemicals used in finishing and furnishing — are one of the most dangerous pollutants found in classroom air.

“Construction materials, furnishings such as desks and shelves, resins of wood products, adhesives, glues, paints, cleaning chemicals, and carpets are primary [volatile organic compounds] emission sources in schools,” the researchers write. “The VOC concentrations in newly built or recently renovated school buildings may be significantly higher than ordinary ambient levels.”

The paper also discusses factors that influence levels of pollution inside schools such as ventilation, temperature, outdoor wind speeds and classroom cleaning protocols.

The researchers point out that research demonstrates a link between indoor air quality and student achievement. Studies “confirm that poor air quality affects both typical schoolwork of pupils, i.e. performance in simple learning tasks such as math and language exercises and pupils’ examination grades and end-of-the-year results,” they write.

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