TRAX Trains Keep Air-Quality Research on Track

By Logan Mitchell, Guest Blogger

DEQ invites guest bloggers to share their thoughts on issues that impact our environment. We appreciate their insights and the opportunity to broaden the conversation with others in the community.

TRAX train sporting an air-quality monitor on top

One great way you can help to reduce emissions and improve air quality is by using public transit. But did you know that the train you’re riding on may also be helping scientists study air pollution along the Wasatch Front?

For the past few years, my colleagues and I at the University of Utah have partnered with the Utah Transit Authority (UTA) and installed air-pollution monitors on two TRAX trains that operate on the Red and Green TRAX lines. We’ve been measuring particulate matter (PM_2.5), ozone (O3), and nitrogen dioxide (NO₂), as well as the greenhouse gases carbon dioxide (CO₂), and methane (CH₄). This project, along with several other innovative projects (such as low-cost PM_2.5 networks from PurpleAir and AQ&U ) as well as the gold standard for air-quality measurements from the Utah Department of Environmental Quality (DEQ) Division of Air Quality (DAQ), have dramatically increased the spatial coverage of air-quality measurements along the Wasatch Front and are leading to new insights into our air-pollution patterns.

What have we learned?

The spatial patterns of air pollution are controlled by emissions, atmospheric chemistry, and daily wind patterns. These factors combine to create gradients in air quality across the city that differ by season and time of day. Understanding these spatial patterns can increase your air-quality awareness and help you plan your daily activities to reduce your exposure to air pollution.

Ozone patterns along the Wasatch Front based on time of day. Click for larger view and to navigate map using Google Earth.

For example, ozone levels measured at DAQ sites in the summertime frequently exceed the National Ambient Air Quality Standards (NAAQS). We know that ozone concentrations are lowest in the morning, but what does that look like spatially across the city?

The TRAX data, averaged during morning hours across the entire summer season, show us what that looks like ( see map). The lowest ozone concentrations can actually be found in the city center in the morning. By mid-day, ozone levels are high due to photochemical reactions driven by strong atmospheric mixing and nitrogen oxides (NO_x) and volatile organic compounds (VOCs) reacting in the presence of sunlight to form ozone.

Late in the evening as the sun goes down, the ozone levels fall, but they are still higher than in the morning. So, if you exercise outdoors along the Wasatch Front in the summertime, the best way to limit your exposure to ozone is to go in the morning.

There are interesting spatial patterns across the city, especially in the morning and evening.  These features are strongly affected by the pattern of combustion across the city as well as air flowing into the valley from the side canyons. Another interesting feature that we’re still investigating is the persistently elevated ozone levels near the University of Utah.

In addition to looking at average conditions, the real-time TRAX air-quality data are posted online so you can see the latest air-quality measurements.

What’s next?

With all of this new data coming in, there are lots of opportunities for new research. First, we’re working on improving the understanding of the relationships between air pollutants and health so we can provide better guidance about the health impacts of air pollution. These data can also help us examine the emission inventories to find out if they are consistent with our measurements. Any discrepancies could point to “missing” emissions and lead to improvements in emission inventories.

Ultimately, our goal is to provide the public and policymakers with the best information possible so they can effectively tackle air-quality issues.

If you’d like to learn more about the TRAX study, check out the research paper we recently published in the journal Atmospheric Environment. Keep an eye on the DEQ blog webpage as well, because we’ll be writing additional blogs for DEQ about our work in the months to come. Stay tuned!

I am an atmospheric scientist at the University of Utah studying emissions and air quality along the Wasatch Front.  In my free time, I enjoy rock climbing, skiing, trail running, gardening, and watching movies.