The Utah Winter Fine Part::Particulate Study (UWFPS) conducted research across the basins of northern Utah, including the Salt Lake, Utah, and Cache Valleys, as well as the Great Salt Lake. The study utilized a NOAA Twin Otter aircraft equipped with a chemically detailed payload alongside multiple ground sites to examine air quality in the region.
The urban air basins located along Utah's Wasatch Mountains serve approximately 2.4 million residents and face some of the most severe particulate matter (PM) air pollution in the nation. In Salt Lake City, concentrations of particulate matter smaller than 2.5 microns exceed the National Ambient Air Quality Standard on average 18 days per year.
Most of these exceedance days occur during December, January, and early February. This period is characterized by winter meteorology that leads to strong, multi-day inversions known as persistent cold air pools. To address these PM2.5 exceedances, the Utah Division of Air Quality is currently developing a State Implementation Plan.
Research indicates that ammonium nitrate is the principal component of regional PM, acting as a secondary species responsible for up to 70% of PM mass during inversions and 40% outside of them. While residential wood combustion is believed to be an important source of organic aerosol during winter in western mountain basins, its specific role in Utah's PM exceedances has not been well quantified.
Because chemical transformations for secondary aerosols like ammonium nitrate likely occur within the cold pool inversion at altitudes above surface level, they are difficult to characterize using ground-based measurements alone. The aircraft flights were designed to characterize emissions, chemistry, transport patterns, and spatial pollutant distributions associated with these exceedances.
The aircraft project involved investigators from the NOAA ESRL Chemical Sciences Division, CIRES, the Utah Division of Air Quality (UDAQ), the University of Utah, the University of Toronto, the University of Washington, and the U.S. Department of Agriculture (USDA). Ground-based investigators participated with support from the UDAQ and EPA.
