New research has documented a direct correlation between absenteeism among Salt Lake City school students and air pollution levels, even at times when air quality is not particularly bad.

An interdisciplinary team led by University of Utah atmospheric scientist Daniel Mendoza examined three years worth of absence data from 36 schools, comparing it with ambient levels of fine particulate matter, or PM2.5, and ozone recorded by a network of sensors set up around the city and mounted on TRAX trains.

It did not establish a causal link between increased school absences and the pollution-trapping inversions that plague the Salt Lake Valley in winter, but the correlation is strong enough to warrant further study, the authors said.

“Air pollution is harmful for not only the health, but also the education and well-being of children in our community,” said co-author Cheryl Pirozzi, an assistant professor in the U.'s Division of Respiratory, Critical Care, and Occupational Pulmonary Medicine. “Even at relatively low levels that many people would not think to be harmful air pollution is associated with increased school absences.”

The new findings build on conclusions drawn by 2014 research sponsored by The Salt Lake Tribune, which documented spikes in school absences in three Wasatch Front school districts during winters with bad inversions. They also affirm what the 24,000-student Salt Lake City School District has long suspected, according to spokeswoman Yandary Chatwin.

(Francisco Kjolseth | Tribune file photo) This Jan. 22, 2014, file photos shows students at Hawthorne Elementary in Salt Lake City staying indoors for afternoon recess because of poor air quality.

“We have noticed these trends in our student population. As we worked with Dr. Mendoza and his team to observe patterns in attendance correlated with poor air quality we noticed it is important for our schools to look throughout the day. At morning recess air conditions will be at one level but by afternoon it will look totally different,” Chatwin said. “The research his team has worked so hard on will be incredibly useful for us to improve our practices. When we have our students back [in school once pandemic restrictions ease] this data will inform how we conduct our recess policies.”

The study has undergone peer review and was accepted Thursday for publication in the journal Environmental Research Letters.

The U. team harnessed air-monitoring data generated between 2015 and 2018 from a growing network of sensors operated by the U. and the Utah Division of Air Quality. The data were so granular the researchers could model pollution levels at the various schools, finding that those on Salt Lake City’s less-affluent west side, which straddles Interstate 15 and rail corridors, often experienced higher levels.

“These are critical because now we can see small nuances, small differences across neighborhoods,” Mendoza said. “Now we can see how one school, for example, had slightly higher or slightly lower values of ozone and particulate matter. And now, instead of looking at the difference between green and yellow days, we can actually see small amounts of variability because of the density of our networks.”

(Photo courtesy of Daniel Mendoza) Daniel Mendoza, research assistant professor in Atmospheric Sciences at the University of Utah, says researchers are able to see small but important differences in air quality between neighborhoods.

Under federal standards, PM2.5 pollution is considered “unhealthy for sensitive groups” at 53.5 micrograms per cubic meter. For ozone, that threshold is set at 71 parts per billion.

The U. research is remarkable because it detected a correlation between absences and air pollution levels far below those thresholds.

“Any pollution is bad,” Mendoza said. “And these lower levels of pollution, which are still harmful to our health, have been understudied.”

The study found that absences increased by a factor of 1.04 across the district for every microgram increase in PM2.5 concentrations.

That might seem like a small number, but it suggests big upticks in absenteeism as fine particulate matter levels get more intense.

“So let’s take a fairly moderate inversion at 50 ug/m3 [micrograms per cubic meter] we get nearly a factor of two, or doubling, of absences compared to a theoretical day with no pollution or 0 ug/m3,” Mendoza said. “Similarly, a really bad inversion, 100 ug/m3, would result in four times the number of baseline absences.”

For days when ozone is elevated, researchers documented a 1.01 increase in absences for every 1 part per billion increase in ozone. Because it forms in response to sunlight, this type of pollution is worst in the summer months, when classes are not in session except at the beginning and end of the school year.

The worst increases in absences occurred on the day after high-pollution events, possibly because reactions to high pollution might reduce exposure and prevent further absences.

But on days after low, yet still elevated, pollution, absences continued to rise on the third, fourth and fifth days of exposure, suggesting a cumulative exposure effect on children’s health, Mendoza said.

“So what that really leads us to think is that even low levels of poor air quality can, in a cumulative manner lead to negative health outcomes — in this case increased school absences. Even on green air quality days, when the pollution was just slightly elevated, if we had several of those days, then kids would still be absent.”

The research documented an apparent disparity between east and west sides of the city, with the west side schools, which serve a larger portion of Salt Lake City’s minority communities, experiencing higher levels of absences. District officials fear the planned development of a massive trade hub in the northwest quadrant of the city could make these disparities worse.

“Because we know how bad the air quality is in our city, we were really concerned when the Utah Inland Port became a reality next to our schools,” Chatwin said. “We have a couple elementary schools where you can stand in the playground where little ones are playing and look into the boundaries of the port.”

In addition to health concerns, school absences also carry an economic cost, particularly when a parent misses work to care for a sick child and kids fall behind in their studies. Factoring lost wages, taxes and productivity due to absences, cutting air pollution by half could save Utah’s economy around $426,000 per year just from reducing absences in the Salt Lake City School District, the research found.

Accordingly, improving school attendance should be considered among the many societal benefits that would result from reducing emissions that pollute the Wasatch Front’s air, the study’s authors argued.