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SALT LAKE CITY — North America's first mobile-based study measuring emissions — via sensors on TRAX trains in the Salt Lake Valley — provides such a critical range of information researchers say it could be replicated in urban centers worldwide.
The study, published online by Atmospheric Environment, collected three years of data from sensors mounted on TRAX trains on the Red and Green lines.
From December of 2014 to April 2017, sensors measured carbon dioxide, methane, ozone and fine particulate matter called PM2.5.
Researchers were able to take advantage of the longest running multisite, urban carbon dioxide monitoring network in the world established in 2001 in the Salt Lake Valley, featuring five sites.
"We know that more data equals better data equals better research, which allows us to come up with better ideas," said Thom Carter, executive director the Utah Clean Air Partnership.
"These sensors allow us to augment our data and get a fuller picture of what is happening around the valley with pollution," Carter said.
The study provided a breadth of information on emission patterns, from the heart of downtown Salt Lake City to less populated areas in the suburbs.
On 400 South, for example, observations showed the highest levels of carbon dioxide along TRAX lines. Researchers noted the heavy vehicle traffic — 20,000 vehicles per day as of 2014 — and multistory buildings that act as an urban canyon.
Sensors on the electrified trains (with zero emissions) transmitted data every five minutes to the University of Utah via cellular communications.
The electric trains, the study notes, present an ideal starting point for emissions research, serving as a blank canvas.
While carbon dioxide was more widely dispersed along study areas, researchers did note distinct plumes of methane around certain industrial areas that included natural gas-fired power plants, a brick factory and landfills.
Those plumes could be associated with daytime industrial activity or in some instances linked to fugitive emissions that could be captured or reduced, according to the study. It also noted that sensors picked up a nitrogen oxide plume associated with a rail yard.
Researchers say these measurements serve as important guideposts. As an example, tracking carbon dioxide in Salt Lake City could be used to monitor fossil fuel emissions and evaluate progress of pollution-reduction targets.
The city has a goal to reduce greenhouse gas emissions by 50 percent in 2030 and by 80 percent by 2040 using baseline data from 2009.
Utah's mobile network of real-time sensors is also unique. Researchers say to their knowledge, only a few other systems utilizing public transportation exist across the globe: Germany, Norway, Switzerland and Italy.
The Salt Lake Valley is an ideal epicenter for the study given its episodic bouts with poor air quality, the high community profile of pollution struggles and localized funding aimed at curbing the problem, according to researchers.
"The combination of poor air quality, wide-ranging interest from the public, stakeholders, governments and regulators, as well as several complimentary resources make the (valley) a unique testbed for evaluating a public transit based atmospheric observation system," the study said.
While this phase of the study used only two light-rail train cars, researchers say it demonstrates the potential for leveraging public transit vehicles as a monitoring platform.
"Other modes of public transit (e.g. electric buses) could also be developed to expand this measurement strategy to other cities to better understand air quality across urban areas worldwide," it concludes.
The University of Utah study was funded in part through grants from the Utah Division of Air Quality, the National Science Foundation and the National Oceanic and Atmospheric Administration.