TRAX air quality study expands

This article, originally published in @theu, February 26, 2020, was written by Paul Gabrielsen, Science Writer, University of Utah Communications

For more than five years, University of Utah air quality sensors have hitched rides on TRAX light rail trains, scanning air pollution along the train’s Red and Green Lines. Now the study, once a passion project of U researchers, has become a state-funded long-term observatory, with an additional sensor on the Blue Line into Sandy and Draper and additional insights into the events that impact the Salt Lake Valley’s air, including summer fireworks and winter inversions.

In a new study published in Urban Science, researchers including Daniel Mendoza and Logan Mitchell report the latest from the TRAX Observation Project, including data validation studies that bolster the data’s value for other researchers and three case studies from recent events showcasing the abilities of the mobile air quality sensors.

What’s new: Blue Line and data validation

UTA’s TRAX system consists of three light rail lines: red, green and blue. Up until November 2019, U sensors measuring ozone and particulate matter were installed only on the Red and Green Line trains, because both lines used the same train cars. These two lines travel through downtown Salt Lake City, the central I-15 corridor and the valley’s west side. With an additional sensor on the Blue Line, however, air quality measurements now extend into the Salt Lake Valley’s southeastern quadrant.

“That’s a really important area of the valley,” Mitchell says. “There’s a lot of people down there.” The Blue Line also goes up and down in elevation, just as the Red Line does as it ascends from downtown Salt Lake City to the U campus. “Since elevation is such a key part of the air quality and understanding the depth of the inversion on different days, under different conditions,” he says, “it’s going to be a really important piece of the dataset for us.”

Extending into the south valley also allows researchers to learn more about how air masses move back and forth between Salt Lake and Utah counties, through the narrow Point of the Mountain passage.

“That’s actually really critical because we sometimes have very different meteorological phenomenon going on between the two valleys,” Mendoza says. “We can now examine in our basin an exchange of air masses.”

The other major development in the TRAX Observation Project is the validation of the data coming from the mobile sensors. This is an important step in a pioneering project such as this, and serves along with quality assurance and quality control protocols as a certificate on the archived data now being made available to other researchers. It also assuages any concerns that the air turbulence caused by the moving train might skew the readings.

The experiment involved a stationary particulate matter sensor placed about 10 feet (3 m) from the rail line that would take readings whenever the TRAX trains were within 500 feet (150 m) of the sensors. Comparing the mobile and stationary readings, Mendoza says, showed 96% accuracy. “That really gives us a great deal of confidence that our TRAX sensors are actually performing really well compared to regulatory sensors and can be used for health studies, policy and so on,” Mendoza says.

Watching the fireworks

With five years of continued observations, the TRAX Observation Project has captured many air quality events. Mendoza, Mitchell and their colleagues document three particular events in their paper: an elevated ozone event from August 2019, a cold air pool inversion event in November 2019 and the fireworks on July 4, 2019.

The fireworks event was unique—it wasn’t a phenomenon caused by an atmospheric event or by the geography of the Salt Lake Valley. It was an incidence of multiple point sources of particulate matter air pollution, allowing observation of how those plumes of particulate matter moved through the valley.

Following generally good air quality, hotspots of elevated pollution started appearing in the TRAX data between 10-11 p.m. on Independence Day. By midnight, the majority of the valley was experiencing moderate to unhealthy air quality.

Mendoza says that the train data shows not only the dispersion of the smoke—something you don’t see in wintertime inversions, which have low atmospheric energy—but also the evening winds coming down Emigration Canyon on the valley’s east side, which washes out some of the air pollution.

“These are examples of the kinds of things that we’re seeing that you couldn’t see with stationary monitors,” Mitchell adds. “It’s helping us understand where the gradients are in the valley, how they evolve through pollution events such as during the Fourth of July or an inversion or an ozone event. You can see the air masses moving around. You can see where the pollution is and how it moves from different parts of the valley.”

Next steps

Next, Mitchell says, the team hopes to add sensors that measure oxides of nitrogen and carbon monoxide, both important components of atmospheric chemistry. They’d also like to expand the study to light rail trains in cities such as Portland or Denver.

“It would be really interesting for us to be able to compare the spatial patterns we’re seeing here with another city that has different topography around it and a different mix of emission sources,” Mitchell says, “so that we can understand how cities, in general, are being affected by these things and how that’s similar or different from what’s going on in Salt Lake City.”

Find the full study here.

Media Contacts

Logan Mitchell | research assistant professor, Department of Atmospheric Sciences

Daniel Mendoza | research assistant professor, Department of Atmospheric Sciences; pulmonary fellow, Division of Pulmonary Medicine, School of Medicine
Office: 801-585-6861 | Mobile: 801-505-8253 | 

Paul Gabrielsen | research/science communications specialist, University of Utah Communications
Office: 801-585-6861 | Mobile: 801-505-8253 | 

Clear the Air Challenge update

This article, originally published in @theu, February 19, 2020, was written by Ayrel Clark-Proffitt, Sustainability Office

We all benefit when the air is clean. That’s the idea behind the statewide Clear the Air Challenge. Every February the University of Utah launches a team as part of a month-long effort to get people out of single-occupant vehicles, which are significant contributors to our air pollution problems.

The U team has hundreds of people logging their sustainable commutes on the TravelWise Tracker. (Psst … It’s not too late to sign up for the U team and log your trips back to Feb. 1.) As of writing this article, the University of Utah team is in first place, though Fidelity Investments, a perennially strong team and defending champs, is right on our heels.

When I look through all the trips we’ve logged this month, I see a few patterns:

Everything is better together

The Clear the Air Challenge winner is judged on CO2 savings, and right now traveling together is getting it done for the University of Utah team. As of Feb. 19, more than three-quarters of the CO2 saved by the U team came from choosing public transit or carpooling over driving alone. Members of the university community can all ride UTA FrontRunner, TRAX and buses by tapping on and off with their UCards. For those that struggle to access public transit, carpooling is a fantastic option. Research Park Connect has done a great job helping its team find carpool and vanpool options.

Health commuters are making a difference

The University of Utah might be in first place, but we wouldn’t be without the efforts of University of Utah Health. The U of U Health commuter team is in third place overall in the challenge. The team is literally breathing new life into the university’s efforts—90% of people signed up for the team are participating in their first Clear the Air Challenge, based on the dates their profiles were created.

It is OK to try new things

We get into habits, we create routines. Often, those are hard to break. Andy Lambert, a graduate student in atmospheric sciences, realized he was on autopilot when it came to his commute, and he made a choice to try out public transit for the first time. He was surprised to find the experience more enjoyable than he expected.

“Normally, my morning routine includes roughly 30 minutes of news and social media time before I can actually leave the house. But with public transit, that 30 minutes can just be moved to time on the bus. How’s that for convenience and efficiency?” Lambert said.

If you are a regular user of sustainable transportation, talk to your friends about it. If you get your pals on public transit, don’t forget to post a photo on Instagram with #CommuteCompanion and tag @SustainableUofU to be entered to win a free gift sponsored by Cotopaxi.

Together, we can make a difference.

Throughout February, take action on air quality by tracking your sustainable commute behaviors with the Clear the Air Challenge, a statewide competition that aims to reduce emissions from vehicles by promoting alternative transit options. Join the U team at travelwisetracker.com/s/university-of-utah. Log trips retroactively back to Feb. 1.

Does public transit reduce pollution?

This article, originally published September 6, 2019 in @theu, was written by Paul Gabrielsen, science writer, University of Utah Communications.

Public transit has long been an answer for people looking to leave their car at home and reduce their air pollution emissions. But now, with better rider tracking tools, the University of Utah and the Utah Transit Authority can better answer the question: How much does public transit reduce pollution emissions?

In a paper published in Environmental Research Communications, University of Utah researchers Daniel Mendoza, Martin Buchert and John Lin used tap-on tap-off rider data to quantify the emissions saved by buses and commuter rail lines, and also project how much additional emissions could be saved by upgrading the bus and rail fleet. The study was conducted in cooperation with the Utah Transit Authority and the Utah Department of Environmental Quality, Division of Air Quality.

High-resolution rider data

Mendoza and his colleagues are certainly not the first to ask how much pollution public transit can save. But a couple of recent technological advances have enabled them to answer the question with a level of detail previously unparalleled.

The first is the advance of tap-on tap-off farecards that provide anonymized data on where those riders who have electronic passes enter and exit public transit. Approximately half of UTA’s passengers use an electronic fare medium. “Now we can truly quantify trips in both time and space,” Mendoza says. “We accounted for all of the 2016 passenger miles by scaling the farecard data, and we know which trips farecard holders make on buses, light rail and commuter rail.”

The second is the General Transit Feed Specification system. It’s the data source that supplies Google Maps with transit information to help users find the bus or train they need. With that data source, the researchers could track where and how often UTA’s buses and trains run.

So, with high-resolution data on the movement of both vehicles and passengers, the researchers could paint a nearly comprehensive picture of public transit along the Wasatch Front.

Balancing emissions

So, with that data, the researchers could quantify the emissions produced and miles traveled of the transit systems (TRAX light rail uses electricity produced outside the Wasatch Front, hence the emissions aren’t in Salt Lake’s air) and balance that with the miles traveled by passengers and the estimated amount of car travel avoided by riding transit.

On weekdays during rush hours, and in densely populated areas, the balance was clearly on the side of reduced emissions. “That tapers off significantly during the evening hours, on the outskirts of the city, and definitely during the weekends,” Mendoza says. In those situations, the number of passengers and how far they rode transit did not offset certain criteria pollutant emissions. (Criteria pollutants are six common air pollutants that the EPA sets standards for through the Clean Air Act.)

For transit to improve its regional reduction in emissions, particularly PM2.5 and NOx, the following strategies, alone or in combination, could be employed: more daily riders per trip, more clean-fuel buses and train cars and/or fewer low-ridership trips.

What-ifs

The current study looks at the bus and train fleet as they are now, with some UTA buses around 20 years old and FrontRunner trains whose engines are rated a Tier 0+ on a 0-4 scale of how clean a locomotive’s emissions are (Tier 4 is the cleanest; UTA is scheduled to receive funds programmed through the Metropolitan Planning Organizations to upgrade FrontRunner locomotives to Tier 2+). So, Mendoza and his colleagues envisioned the future.

“What if we upgrade all these buses, some of them from 1996 or so?” Mendoza says. “They emit a significantly larger amount than the newer buses, which are 2013 and newer.”

What if, they asked, UTA upgraded their buses to only 2010 models and newer, fueled by either natural gas or clean diesel? And what if the FrontRunner engines were upgraded to Tier 3?

Emissions of some pollutants would drop by 50%, and some by up to 75%, they found.

“Now, with this information, UTA can go to stakeholders and funding agencies and say, ‘Look, we’ve done this analysis,” Mendoza says. “This is how much less we can pollute.’”

Mendoza adds that taking transit offers additional benefits besides reducing air pollution. Taking transit gives riders time to read, work or listen while traveling. How does Mendoza know? He’s a dedicated transit rider. “I always get to where I need to go pretty much on time and completely unstressed,” he says. “I almost never drive.”

Find the full study here.