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Cache Valley: Science
The Cache Valley and the Wasatch Front are very different in people's eyes. Many describe the cache Valley as a bucolic agriculturally based small town, while the Wasatch Front is the congested urban neighbor. Surprisingly, the concentration and type PM2.5 pollution is very similar in both areas. Both regions share similar characteristics including valley-mountain topography, strong winter-time temperature inversions, and a type of PM2.5 that is formed when gaseous pollution reacts in the air to form particles. The sources and mixes of gaseous pollution in both regions are similar enough that the dominate chemistry pathways are the same.
There are, however, two major differences between the Cache Valley and the Wasatch Front. The first difference is that the Cache Valley is entirely enclosed by mountains and this results in stronger and more persistent temperature inversions compared to the Wasatch front. Secondly, the Wasatch Front has many more people and more large industry pollution sources compared to the Cache Valley. The Cache Valley features smaller commercial and agricultural pollution sources. These differences have the potential to impact the emission control strategies that are ultimately selected by stake holders.
How do inversions impact air quality?
Surface temperature inversions play a major role in air quality, especially during the winter when these inversions are the strongest. The warm air above cooler air acts like a lid, suppressing vertical mixing and trapping the cooler air at the surface. As pollutants from vehicles, fireplaces, and industry are emitted into the air, the inversion traps these pollutants near the ground, leading to poor air quality. The strength and duration of the inversion will control air pollution levels near the ground. A strong inversion will confine pollutants to a shallow vertical layer, leading to elevated PM2.5 concentration levels, while a weak inversion will lead to lower PM2.5 concentration levels.
Ammonium Nitrate Chemistry
There are many types of particulate that constitute PM2.5. Both Wasatch Front and Cache Valley PM2.5 are dominated by a particulate called ammonium nitrate. Ammonium nitrate is a particle that is formed when gaseous pollution chemically reacts in the air to form a particle. Ammonia gas and a form of nitrogen oxide gas are the direct precursors to the formation of the ammonium nitrate particle. Ammonium nitrate readily forms and persists in cold temperature environments.
Ammonia gas is produced by agricultural activities and waste treatment. It reacts directly with gaseous nitric acid to form ammonium nitrate particulate. Nitric acid is formed through a complex series of reactions that involve sunlight, nitrogen oxides, and volatile organic compounds (VOCs).
NH3 (gas) + HNO3 (gas) <-->NH4NO3 (particle)
Ammonia + Nitric Acid <-----> Ammonium Nitrate
For more information or questions contact : Bill Riess (801-536-4077), or Tyler Cruickshank (801-536-4468).
