Using Low-Cost Air Sensors in Schools Can Inform Decision-Making

Measuring air pollution from wildfire smoke at schools and child care settings could help staff make informed decisions that can reduce children’s exposure to smoke. Researchers at the University of Washington partnered with four Washington state schools in areas frequently affected by wildfire smoke to test a process for measuring in-school air pollution.

“Children are especially vulnerable to health impacts from air pollution because they breathe in more air relative to their body weight compared to adults, their lungs are still developing, and they are often very active,” said lead researcher Orly Stampfer, Ph.D., now at the Washington State Department of Health (WA DOH). “Measuring air pollution during wildfire smoke events could help school and child care staff determine whether to adjust activities to help protect children from harmful exposure.”

The research team examined whether and by how much air pollution measurements varied across rooms within the same school, and how indoor air quality compared with outdoor air quality during a wildfire smoke event. Results of the study are published in a May 2024 paper.

Setting up Sensors and Collecting Measurements

Researchers worked with school staff to determine where to place sensors inside the schools. They used Purple Air sensors because they are low cost and easy to install. Staff identified priority areas to measure where students would spend the most time, such as classrooms and the gym. The gym is particularly relevant because doing vigorous physical activity in the event of poor air quality can be particularly risky to children’s health. Staff also identified areas where they expected air quality to vary because of differences in ventilation and air filtration.

The researchers’ findings indicated that air quality readings varied widely across rooms within the same facility. This showed that taking measurements in multiple locations, as would be done with a handheld sensor or multiple sensors throughout a school, gives the clearest picture of children’s risk of exposure to air pollution.

The team also installed one outdoor sensor at each school. Outdoor and indoor data were used to calculate the ratio of indoor to outdoor fine particulate matter concentrations, which is a common method of assessing variability in indoor air quality.

Since setting up multiple sensors may not be practical for schools due to financial or other reasons, the research team used their data to simulate the use of a handheld sensor that staff could use to take measurements while walking around a school, which would be a likely way school staff would take measurements on their own. Based on their findings, the team recommends that if a school is going to rely on handheld sensors for a general understanding of their indoor air quality, staff should take measurements using handheld sensors multiple times throughout the wildfire smoke event. For decisions about activities happening in the very near future, such as deciding at the last minute whether to have outdoor recess, current handheld sensor data can be useful.

The team also examined how well historical measurement data predicted air quality over the next hour. They compared the average of either 3 hours or 10 minutes of measurement data to air quality over the next hour. Indoors, the average from the 10 minutes before the hour predicted air quality over the next hour better than the 3-hour averages. Outdoors, 10 minute and 3-hour data predicted the next hour similarly. This shows that decisions about air quality indoors are best made with the most recent sensor readings.

“Air quality during wildfire smoke can sometimes be stable, but also can change substantially over a short span of time,” stated Stampfer. “When using sensors to inform decisions about children’s activities, recent, short-term measurements can be really helpful to make decisions about activity location or intensity for activities happening in the next hour.”

Developing a Toolkit for Air Quality Measurement in Schools

The study’s results have already informed guidance from WA DOH on using low-cost sensors to support decision-making during wildfire smoke. While guidance on using low-cost air sensors exists from sources such as the Environmental Protection Agency (see also the July 2024 PEPH mini article on EPA reports on using low-cost sensors), the guidance from WA DOH is specifically tailored to child and youth settings and is meant to be more accessible to school and child care staff.

The team has previously interviewed school staff about their perceptions on using air sensors to make decisions to protect children’s health. Results indicated that schools may have limitations as to what type of sensors they can use, due largely to cost considerations, but also related to the time to use and read the sensors. These perceptions informed the current study, particularly the use of low-cost sensors, and simulation of walkaround measurements.

Stampfer will continue working with the air quality team at WA DOH and plans to use the results of those interviews when developing toolkits for schools and child care settings.

“Our goal is that the toolkit will provide guidance on selecting and using sensors, as well as interpreting sensor measurements to help inform decisions,” added Stampfer. “This supports the overall aim to reduce children’s exposure to poor air quality from wildfire smoke.” Listen to the July 2021 PEPH podcast to learn more about children’s health and wildfire smoke.

Listen to the July 2021 PEPH podcast to learn more about children’s health and wildfire smoke.