For all of the majestic, mountain-ringed landscape that Utah’s Great Salt Lake region embodies, local residents can encounter a threat to their health each winter as the atmosphere succumbs to a thick smog.
To help local officials develop mitigation strategies, Dr. Alexander Moravek and his collaborators wanted to pin down the composition and source of the particulate matter that makes up the smog.
This project, better known as the Utah Winter Fine Particulate Study (UWFPS), was a collective effort between the National Oceanic and Atmospheric Administration (NOAA), the Utah Division of Air Quality, the Environmental Protection Agency, and several universities.
Conducted in 2017, while Moravek was a postdoctoral fellow in the University of Toronto’s Department of Chemistry, some of the results of the UWFPS were published late last year.
The work focused on emission sources of ammonia as a major precursor of the fine particulate matter, which combines with the region’s topography to form the notorious smog. More specifically, ammonia and nitrogen oxides mix to form ammonium nitrate aerosols.
This hazardous mixture, coupled with temperature inversion, forms the Great Salt Lake region’s smog during the winter months.
The smog is made up of particles that are 2.5 micrometers or smaller in diameter (about 1/20 the diameter of a strand of hair).
Their small size allows them to pass through our lungs and enter the bloodstream, where they can wreak havoc on the cardiovascular and respiratory systems.
During an inversion, high-pressure systems create a stably layered atmosphere, which prevents the air from mixing and causes particulate matter to pool at the bottom. The Great Salt Lake region’s mountains exacerbate this effect.
Government officials and Moravek’s team knew that ammonia-containing aerosols were predominant contributors to the smog in Utah’s Great Salt Lake region. But they knew little about their source or chemical composition.
To find out, Moravek and his collaborators would need to sample ammonia and particulate ammonium together with other trace gases and particulate compounds over the Great Salt Lake region. The researchers collected and measured air samples using a quantum cascade tunable infrared laser differential absorption spectrometer aboard NOAA’s Twin Otter aircraft.
“The important feature of the instrument is that it is fast enough to be able to resolve the spatial distribution of ammonia while the aircraft is moving,” says Moravek, who is now a postdoctoral researcher at York University.
An aerosol mass spectrometer was used to measure the fine particulate matter composition while a cavity ring down spectrometer measured nitrogen oxides.
“It was a relatively small aircraft that enabled us to measure the lowest part of the atmosphere, the so-called atmospheric boundary layer,” says Moravek. “[This] is where all the interactions with the ground take place, where all the emissions are, and as well as a lot of the chemistry is happening.”
The aircraft traversed the Great Salt Lake region for more than four weeks, logging a total of almost 60 hours of airtime.
“What we found was that ammonia emissions in those inventories were underestimated by a factor of four to five due to underrepresentation of agricultural emissions,” says Moravek.
This underestimation was the most significant for Cache Valley, which is known for its agriculture activities. While wintertime air pollution is an issue in other parts of the United States, agriculture activities have markedly worsened the Great Salt Lake region’s air quality.
As well, Moravek and his co-authors found that 70 per cent of nitrogen oxides in Cache Valley were due to emission sources from neighboring regions, like Salt Lake City, during pollution periods.
“Since nitrogen oxides emissions are higher in nearby counties with higher vehicle and more industrial sources, a substantial amount of nitrogen oxides is mixed into Cache Valley from other counties,” says Moravek.
Determining the source and composition of the emissions is just one part of the UWFPS. Moravek and his collaborators delve into the chemical formation processes of the fine particulate matter in other publications from the project.
To further understand these processes and develop mitigation strategies, follow-up studies are set to take place in 2021 and 2022.