December 30, 2018

Air quality project measures pollution in one of the fastest developing areas in the nation – the Wasatch Front

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by Daniel Mendoza

The TRAX Air Quality Observation Project was started by the Department of Atmospheric Sciences at the University of Utah in December of 2014 and has been recording air quality measurements across Salt Lake County continuously since its inception. The Salt Lake Valley is vulnerable to high levels of pollution, including fine particulate matter (PM2.5) and ozone.

PM2.5 refers to any particle that is 2.5 microns or smaller in size. As a reference, the width of a human hair is approximately 50-70 microns and human eyes cannot see anything smaller than about 40 microns. Therefore, these are very small particles that can penetrate deep into the lungs and cause similar health impacts as cigarette smoking.

Ozone is a gas that can form highly reactive free radicals upon exposure. The effect has been likened to getting a sunburn in the lungs and is the reason why many people develop a dry feeling accompanied by cough and some chest pain when they are exposed to high levels of ozone.

Two light rail TRAX cars, operated by the Utah Transit Authority, have been outfitted with sensors to measure and record ozone, PM2.5, carbon dioxide, and methane at a sub-minute resolution using research-grade equipment. These trains typically travel on the Red and Green TRAX lines covering the majority of Salt Lake County and the data is available in near real-time from:

Some of the most important findings from this project are the large differences in pollutant concentrations measured across Salt Lake County. The highest recorded PM2.5 levels were found during winter inversion periods on the 400 South transect from the University of Utah’s Stadium to the Salt Lake City Library stations, as well as on the transect from the Courthouse to the Fashion Place West stations. These are the some of the lowest elevation areas in the Salt Lake Valley located next to large pollutant sources from traffic.

Conversely, the highest measurements of ozone were found during the summer near the Daybreak and University Hospital stations, areas of high elevation on the foothills of the Wasatch and Oquirrh Mountains. It is important to inform the public about the dangers of high levels of invisible ozone in the foothills and mountains adjoining the Salt Lake Valley, as these areas are frequented by recreational users during the summer months and, unlike PM2.5, ozone is not visible to the human eye.

This year the TRAX air quality observation project, which was in danger of being cancelled, was funded through a successful appropriation request by Sen. Luz Escamilla and Rep. Angela Romero. All new air quality sensors were installed on November 19, replacing the aging original sensors. The original sensors were donations from various research teams at the U, and Siemens provided the equipment box that house the instruments on top of the train. UTA provided invaluable in-kind support from technicians and staff.

One of the main areas of interest for the TRAX data is the verification of the impact of various air quality policies and environmental forensics, also known as the study of the evolution and transport of contaminants. A clear example of this was the finding of the Roper Railyard as a significant source of nitrogen oxide emissions. (Although the Salt Lake Valley does not generally suffer from elevated nitrogen oxide levels, this particular gas is a precursor to ozone and PM2.5 formation.) The Green TRAX line crosses I-15 as it heads west toward West Valley City and passes next to the Roper Railyard. During analysis of the recorded data, we found two spikes, or hotspots, near I-15. One of these peaks was attributed to I-15, but the other, of similar magnitude, was not immediately obvious.

After closer inspection, the team identified the source as the train railyard, and more specifically, the locomotive switchers. This led to a bill proposed by Rep. Steve Handy to upgrade these switchers during the last legislative session. Had the bill passed, we would have been able to measure the impact of these upgrades on nitrogen oxide readings and report any observed reductions.

While the TRAX observation project measures the here and now, we must be cognizant of what we expect in the not so distant future. The Wasatch Front is one of the fastest developing areas in the United States. Projections estimate a doubling of the population by 2040 or 2050 from 2010 baseline values.

Another study from the U of U Dept. of Atmospheric Sciences, has quantified the impacts of population growth and climate variability on future emissions for Salt Lake County. These estimates take into account the residential, commercial, and on-road (vehicular traffic) sectors. The growth in urban environment is derived from models developed by the Wasatch Front Regional Council which span from sprawl to compact growth. These in turn inform whether large, stand-alone single-family homes or apartment buildings will be built in specific regions of the county, and what the road network will look like to serve these communities. Furthermore, office buildings and other commercial buildings were modeled to account for increased employment.

Preliminary findings show that a projected temperature increase will cause reductions in natural gas consumption used for building heating during the winter, but will increase cooling demands in buildings and cars. Several mitigation strategies, including increases in fuel efficiency and increases in electric vehicle adoption, as well as improved heating, ventilation, and air conditioning (HVAC), water heating, and lighting in buildings were considered. Furthermore, an increase in renewable energy usage to power electricity generation was included in the model, which eliminates fossil fuel combustion.

Our results show that Salt Lake County can achieve significant energy consumption and emissions reductions and reach ambitious targets proposed by several city and local leaders.

Dr. Daniel Mendoza is a Research Assistant Professor at the University of Utah, Dept. of Atmospheric Sciences, and Pulmonary Fellow at the School of Medicine at the University of Utah.