A visualization of average carbon dioxide levels around the Salt Lake Valley, measured on the TRAX red and green lines between December 2014 and April 2017. (Logan Mitchell)

Double duty: Utah puts sensors on public transit to monitor air quality

One day in January 2017, Salt Lake City, Utah, earned the dubious distinction of having the worst air quality in the nation. Unfortunately for residents, researchers have found that air pollution levels in the Salt Lake Valley exceed U.S. National Ambient Air Quality Standards for about 40 days each year. The nearby mountains and the Great Salt Lake trap pollutants at the elevation level where the majority of Salt Lake City residents live.

To study how air quality varies in different areas of the city over time, University of Utah researchers attached sensors to the top of a train car in the Utah Transportation Authority’s TRAX light rail system as it travels a 45-mile route. The sensors take measurements once per second, measuring hazardous particulate matter as well as levels of in the air. Every five minutes a cellular modem in the box housing the sensor transmits time, location and pollution level data to servers at the University of Utah.

Rather than having to rely on pollution monitors in fixed locations, the train-mounted sensors give researchers a way to take regular spatiotemporal readings and create real-time high-resolution maps of air pollution across urban areas.

“Based on averages, we are able to understand where the hot spots are and the gradients  of the air quality across the city,” Logan Mitchell, lead researcher in the university's Department of Atmospheric Sciences, said.

Mitchell uses MATLAB software to make sense of the data.  He plots the data around grid points along the train lines and averages the readings based on location to make the data more manageable.    Averages over time of day and seasons create a more comprehensive picture of how the air quality levels change over time, helping track pollutants, sources and trends.

All of this data is also shared with the public through the MesoWest project, a collaboration between the University of Utah and the National  Weather Service that collects and provides access to current and archival weather data from over 20,000 weather stations. The data can be downloaded or accessed via an application programming interface.

In addition to posting data from the TRAX train sensor for the Salt Lake Valley, the MesoWest Utah website also includes data from stationary sensors from the state's Division of Air Quality and the citizen science group Purple Air.  

While the Utah DAQ has been receptive to getting the data from the university's train-mounted sensor, the information is not being used for regulatory purposes, Mitchell said.

The next stage for researchers is getting more funding to drill down further into the sensor data.

“We want to look at how the chemistry behind the particulate matter and ozone is created since we want to determine how these processes that create emissions effect air quality,” Mitchell said.  “We are also looking to test a hypothesis on whether spatially resolved data will  provide better estimates of air quality at different locations at different times.”

About the Author

Sara Friedman is a reporter/producer for GCN, covering cloud, cybersecurity and a wide range of other public-sector IT topics.

Before joining GCN, Friedman was a reporter for Gambling Compliance, where she covered state issues related to casinos, lotteries and fantasy sports. She has also written for Communications Daily and Washington Internet Daily on state telecom and cloud computing. Friedman is a graduate of Ithaca College, where she studied journalism, politics and international communications.

Friedman can be contacted at sfriedman@gcn.com or follow her on Twitter @SaraEFriedman.

Click here for previous articles by Friedman.

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