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Utah Winter Fine Particulate Study (UWFPS)

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Executive Summary

Northern Utah valleys experience elevated levels of particulate matter less than 2.5 micrometers in diameter (PM2.5) in winter. These pollution episodes are closely associated with periods of atmospheric stability known as Persistent Cold Air Pools (PCAPs) or, more commonly referred to as inversions. A typical Utah winter sees about 5 to 6 multi-day inversion episodes and on average, 18 days with high PM2.5 levels exceeding the National Ambient Air Quality Standard (NAAQS).

The majority of the PM2.5 that builds up during these episodes are secondary particulates, meaning they are formed in the atmosphere via reactions of gas-phase precursors and are dominated by secondary ammonium nitrate. Better understanding of the mechanisms driving these pollution episodes and identification of the most important chemical species for the formation of PM2.5 are needed in order to develop effective control strategies to reduce particulate levels.

A pilot study was conducted by DAQ (Division of Air Quality)on the chemical processes relevant to fine particulate pollution during the winter of 2015-2016 in collaboration with researchers from local universities and NOAA. This work, led by Dr. Munkh Baasandorj (DAQ and University of Utah), showed the importance of complex interactions between chemical processes that form PM2.5 and the meteorological processes that are responsible for mixing the PM2.5 and other pollutants within the inversion layer. Building on this pilot study, the UWFPS will investigate the chemistry, transport, and spatial and vertical distribution of species relevant to particulate formation by deploying NOAA’s specially equipped light aircraft known as the Twin Otter. The aircraft will fly over the Cache, Salt Lake, and Utah valleys from January 15 to February 14, 2017, to survey the chemical conditions responsible for the formation of PM2.5. This study aims to address the scientific uncertainties surrounding winter PM2.5pollution. Among many questions this study addresses, DAQ is particularly interested in answers to the following questions:

  • What are the most important chemical mechanisms for the formation of ammonium nitrate?
  • What are the most important reagents in the formation of PM2.5?
  • What are the sources of these pollutants?
  • Where are the emission “hotspots” in each valley?
  • How do the pollutants vary temporally, spatially, and vertically?
  • What is the role of Great Salt Lake or Utah Lake in PM2.5 formation?

The resulting data collection and analysis will be shared with technical and policy analysts at DAQ. Relevant findings will be incorporated into the air quality modeling process so DAQ can accurately evaluate the pollution reduction potential of proposed rules and regulations. In a broader sense, the results of this study will be critical to develop a better scientific understanding of the chemistry and transport mechanisms driving these winter particulate pollution events, provide constraints to improve modeling capacity and identify model deficiencies, and ultimately improve winter air quality in many areas with PM2.5exceedences.

Relevant Documentation

The Utah Winter Fine Particulate Study (UWFPS) is a collaborative project between scientists from the  Division of Air Quality, the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL) and the Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, the Environmental Protection Agency (EPA), United States Department of Agriculture (USDA), University of Utah, University of Washington, University of Toronto, University of Minnesota, Utah State University, and Brigham Young University.

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