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Utah’s TRAX air monitoring study expands to include the Blue Line

By Amy Joi O'Donoghue, KSL | Posted - Mar. 8, 2020 at 6:16 p.m.



SALT LAKE CITY — One of the few areas of the globe where public transit is a permanent fixture for sensors to document air pollution just received a boost to gather more information, and Salt Lake Valley residents are the unique beneficiaries of what will be found.

The more than five-year study of the valley’s air pollution patterns using the Utah Transit Authority’s TRAX light rail system recently expanded to include the Blue Line, which covers the southeast quadrant of the county.

The Red and Green lines have been host to the air quality monitors since 2014, measuring pollution hot spots throughout downtown, at the higher elevation at the University of Utah and west to Daybreak.

“UTA has been a fantastic partner,” said Logan Mitchell, a research associate in the university’s Department of Atmospheric Science.

The surveillance effort received additional money from the Utah Division of Air Quality for sensors on the Blue Line.

Mitchell said the addition of that geographic area will be beneficial because of the number of people who live in that section of the valley and the fact that the Blue Line encounters changes in elevation, just as the Red Line does.

“It is going to be a really important piece of the dataset for us,” he said.

The mobile sensors are providing new insight into where, why and how air pollution spikes and how those patterns vary. The information also augments other research efforts.

In a new study published in Urban Science, Mitchell and Daniel Mendoza, a research assistant professor in the university’s Department of Atmospheric Science, detail the latest findings from what is called the TRAX Observation Project.

The sensors provided data on levels of PM2.5, or fine particulate matter, on levels of ozone, carbon dioxide and methane. In particular the study focused on three separate pollution events in 2019: elevated ozone levels in August, the July Fourth fireworks celebration, and a winter inversion in November.

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For July Fourth, the sensors picked up pollution spikes from seven large public firework displays in the valley. The data mapped the corresponding increases in pollution as a result of the celebrations that drove air pollution to moderate to unhealthy levels.

In the inversion event, the sensors mapped how air quality started out good in much of the valley during the early morning hours but degraded during and after the morning rush hour around the interstate highways and lower elevations of the valley. The moderate air quality conditions persisted after the afternoon rush hour except in the foothills in the northeast area of the valley due to canyon winds and toward the Great Salt Lake likely due to breezes.

“All these complicated wind patterns affect air quality in the city,” Mitchell said, adding it is difficult to model.

The TRAX mobile effort is unique, he said.

There has been temporary deployment of mobile sensors in Brisbane, Australia; Beijing; and Ontario, Canada, but Mitchell said he’s only heard of a few other permanent deployment of air quality sensors on public transit, and those are in Asia. One project in Zurich is no longer active.

There’s not very much science out there in this arena, he emphasized.

“I think we are really breaking new ground here in terms of deploying instrumentation and actually using it to study what is going on.”

Amy Joi O'Donoghue

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