Research Spotlight: Air Quality Monitor Takes a Ride on Trax

Air quality monitoring equipment mounted on a UTA TRAX train. Photo courtesy of Dr. Logan Mitchell.

Air quality monitoring equipment mounted on a UTA TRAX train. Photo: Dr. Logan Mitchell.

By Hilary Smith, Sustainability Resource Center

Air. It’s the most fluid and ethereal of the earthly elements, characterized by its purity, transparency, and capacity to sustain organic life. What the air carries, however—particularly in Salt Lake winters—is clearly, or un-clearly, a different story.

View from Little Cottonwood Canyon:  pollution trapped in a winter inversion. Photo: Laura Schmidt

View from Little Cottonwood Canyon: pollution trapped in a winter inversion. Photo: Laura Schmidt

Last fall, a group of U of U researchers collaborated on a project to better quantify the concentrations of greenhouse gases and pollutants that hover, in varying concentrations, over the valley. The researchers—from the Land-Atmosphere Interactions Research (LAIR) group and the Mountain Meteorology group, both part of the University of Utah Department of Atmospheric Sciences— mounted air quality and greenhouse gas monitoring equipment under the driver’s seat on a red line UTA TRAX train, which gathered data as the train moved back and forth from the U to its southern terminus at Daybreak. The pilot ran from Aug. 11-Sept. 12, 2014.

That data proved so useful that the project was recently expanded and retooled to focus on the dangerous pollutants that are trapped in the winter inversion. Data from both the pilot project and the current project are available online.

Dr. Logan Mitchell, who is heading the UTA TRAX air quality monitoring study. Photo:

Dr. Logan Mitchell, lead researcher on the UTA TRAX-mounted air quality monitoring study. Photo:

Dr. Logan Mitchell, who has spearheaded the effort, says the red line is ideal for studying the spatial distribution of greenhouse gases and air pollutants. This is because it covers a large section of the valley, from north to south and east to west, and because it hits multiple elevations, traveling from the nearly-identical higher elevations at both ends of the route through the lower valley bottom in the middle. “If someone had asked me to design a public transit line that is also ideal for atmospheric sampling, I would have designed the red line,” he says.

The monitoring equipment isn’t new; it’s the mounting of it on a moving platform that is innovative, notes Mitchell. He adds that this is the first train-mounted air quality monitoring system employed in the United States. “The UTA has been incredibly helpful and generous with their time—they have really facilitated this project,” he says.

Mitchell recently walked me through the data from the summer pilot project and described some of its most interesting findings.

The pilot monitored three different greenhouse gases: carbon dioxide, a prevalent greenhouse gas whose human-caused production results mostly from the burning of fossil fuels; methane, a potent greenhouse gas that traps 86 times the amount of heat as carbon dioxide over a 20-year time period; and ozone, a greenhouse gas which, when inhaled, can cause chest pain, coughing, throat irritation, congestion, and a variety of other symptoms. Ozone concentration tends to be higher in the summer, because sunlight is one of the primary ingredients in its production. Mitchell notes that there are no direct health risks posed by either methane or carbon dioxide at the levels at which they occur in Salt Lake, but carbon dioxide is co-emitted with other pollutants and thus can be used as a proxy to understand their emission patterns. Measuring greenhouse gases also helps researchers better understand the scale and dynamics of climate change on a local level.

Pilot project data showed that carbon dioxide emissions varied predictably throughout the day and throughout the valley, spiking higher near places like the I-15 and I-215 corridors, where vehicle traffic is heaviest.

The methane results were similarly predictable, says Mitchell: low levels throughout the train route, with a spike near the train’s Daybreak terminus, which is located near a landfill. (Landfills, he notes, are known to release high levels of methane.) Much smaller spikes in methane were noted in Murray and a few other areas. Mitchell says he suspects these are related to leaks in natural gas infrastructure, and he hopes that this research will eventually help to quantify emissions of this type.

The ozone data told an interesting story.

Ozone increased throughout the day, peaking in the heat of the afternoon and sinking to its lowest levels across the board in the night and early morning. This, explains Mitchell, is in keeping with what we generally know about ozone:

  • Ozone is formed by the mixing of two components—nitrous oxide and volatile organic compounds (VOCs), which are emitted by power plants, factories, cars and trucks—in the presence of sunlight.
  • Later, in the absence of sunlight, the ozone is consumed by the nitrous oxide, and ozone levels are reduced.

What the monitoring data demonstrated, and what surprised researchers, was the power and hunger of that nitrous oxide in consuming the ozone. Near areas of highest car traffic—again, I-15 and I-215 corridors—ozone levels were lower, even in the heat of the day, while they were spiking elsewhere.

Screen shot of a 3-D representation of ozone measurements, results of a summer 2014 pilot TRAX-mounted air quality study.

Screen shot: A 3-D representation of ozone measurements, results of a summer 2014 pilot study.

Mitchell says the team was surprised by the relative soundness and clarity of the data from the pilot study. A website was developed to share the results with the public, as well as with health researchers, legislators, and other scientists studying atmospheric dynamics and chemistry. But it wasn’t long after the preliminary data had come in that the team started thinking about using the mounted, mobile sensor technique to study air pollutants during inversions.

Inversion season—so-defined because it is the time of year, roughly from November to February, when climatological conditions potentially allow inversions to occur—offered the team an opportunity to measure not just greenhouse gases, but also PM 2.5. These particulates are believed to cause numerous long-term and short-term health effects when inhaled, including cardiovascular effects, cancer, harmful developmental and reproductive effects, and respiratory struggles such as coughing, wheezing, shortness of breath, and exacerbation of asthma symptoms.

A new chapter of the project started on Dec. 8, when the team restarted their monitoring on TRAX trains. The under-seat monitor was reconfigured into a metal box, which is now located on top of the train. Carbon dioxide and methane monitors remain, but the ozone monitor has been replaced by a PM 2.5 detector—a piece of equipment that uses a light sensor to count particulates. The new equipment rides on a train that runs alternately on green and red TRAX routes. Real-time PM 2.5, methane, and carbon dioxide data can be viewed online, for free, via a website designed by atmospheric sciences PhD candidate Alex Jacques.

The UTA TRAX-mounted air quality monitoring project now features a new metal container for its sensors, which rides on top of the train rather than underneath the seat of the driver.

The project now features a new container for its sensors, which rides on top of the train rather than underneath the seat of the driver. Photo: Dr. Logan Mitchell

Building that site was tough, says Jacques, because he had to do it before the

U of U Atmospheric Sciences PhD candidate Alex Jacques put together the public web site that displays study results. Photo:

U of U Atmospheric Sciences PhD candidate Alex Jacques, creator of the public web site that displays the study results. Photo:

instruments had been installed—and thus, before any meaningful data were available. “Once the instrumentation was up, it was much easier to make modifications so that data was displayed more effectively,” he says. Both Mitchell and Jacques note that they would like to further tweak and expand the website in the future, employing maps from Google Earth to display real-time data in three dimensions.

“Personally, I have very much enjoyed being able to contribute to this project by creating an interactive interface that allows users to visualize the data,” says Jacques.

Mitchell agrees. He says that he’s never worked on a project where the data has been so easily accessible to the public and to other researchers. While he notes that the real-time data is preliminary and the project is still young, he hopes to expand its reach in the future, securing dedicated equipment for the project and expanding the monitoring to more trains and routes.

Overall, Mitchell says he is glad that the public and the media have expressed such enthusiasm for the project. “I’m excited to see people interested in the science,” he says.

Hilary Smith is a graduate student in Environmental Humanities and a graduate assistant in the Sustainability Resource Center. Research Spotlight is an occasional feature on SustainableUtah. Please send suggestions for future Research Spotlight subjects to

One response to “Research Spotlight: Air Quality Monitor Takes a Ride on Trax

  1. Pingback: Using Urban Infrastructure to Measure Air Quality | Global Change & Sustainability Center·

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