By Chris Pennell
Air pollution has become a growing public-health concern. Poor air quality creates acute and chronic problems. Finding effective solutions to Utah’s unique air quality concerns relies on gaining a comprehensive understanding of the sources and chemical makeup of the pollution.
On Saturday, Aug. 10, researchers from Utah Department of Environmental Quality’s Division of Air Quality (DAQ), the U.S. Environmental Protection Agency (EPA), the University of Utah (U of U), Utah State University (USU), and Brigham Young University (BYU) finished gathering data for the Wasatch Front Ammonia and Chloride Observations (WaFACO) study.
The Wasatch Front Ammonia and Chloride Observations is looking at the role ammonia, a poorly understood chemical in air pollution, plays in the formation of the fine particulate pollution that clogs Northern Utah skies during wintertime inversions.
Ammonium nitrate starts as two gases: oxides of nitrogen (NOx) and ammonia (notice no ‘M’ at the end). Oxides of nitrogen are produced whenever something is burned. These emissions come from your fireplace, your car, or the smokestack of a factory, among others.
On a bad winter day, up to 70 percent of the airborne particulates, called PM2.5 because they measure less than 2.5 microns, are ammonium nitrate. When NOx enters the atmosphere, it begins to combine chemically with oxygen—what scientists call oxidization. During the oxidization process, the NOx changes and becomes nitric acid.
All the combinations aren’t done, though.
The nitric acid grabs onto the ammonia and creates ammonium nitrate. During these combinations, the two gases go from being a vapor to being a solid. This newly created solid is—you guessed it—smaller than 2.5 microns.
As researchers, we know where the NOx is coming from—cars, fireplaces, and factories. It’s less clear where the ammonia is coming from. The WaFACO study hopes to locate some of these sources of ammonia so we can better regulate their emissions.
The researchers in the WaFACO study set up air monitoring sites from Brigham City to Mona. These monitors housed specialized instruments that measured levels of ammonia and hydrochloride acid (HCl)—another precursor of PM2.5. Since February, these monitors have been collecting valuable data that will give us the most comprehensive look at the levels and locations of ammonia along the Wasatch Front.
Over the winter, students from USU, BYU, and U of U, helped collect samples at these. In addition to gathering data from these monitoring stations, EPA sent out a mobile monitoring van. The van allowed scientists to gather measurements of gaseous ammonia on the go. The scientists drove up and down the Wasatch Front collecting data at multiple locations—on the freeway at rush hour, next to farmers’ fields, by landfills, and at industrial site.
This summer, students continued to collect data as the scientists at DEQ’s Division of Air Quality processed the information collected during the winter.
At this point, the team is hesitant to draw any conclusions, but the evidence points to a few interesting trends.
First, we don’t know all the sources of ammonia, but we do know that concentrations of ammonia change from one season to the next. Researchers saw geographic and seasonal variations in the concentrations in Salt Lake Valley and Utah Valley. As the data are analyzed, the team hopes to have a better idea of where these seasonal sources come from.
Next, ammonia in Utah Valley is at least twice as high as in the Salt Lake Valley. This is probably due to agriculture and comes from fertilizer and other farm-related emissions. Transport from the southern valley north seems to play a role in the severity of PM2.5 pollution in Salt Lake County. There appears to be a strong contribution of Utah Valley’s pollution to the Salt Lake Valley’s pollution.
Lastly, mobile sources—cars and trucks—seem to be important source of ammonia. Researchers had suspected that mobile sources played a role, and the data confirms that, in addition to NOx emissions, automobiles are a key contributor to ammonia in the atmosphere. In fact, we suspect that ammonia emissions from mobile sources may play a more important role in PM2.5 formation than NOx emissions.
To better inform pollution control strategies in Northern Utah, it is necessary to understand the complex chemical and physical processes that create PM2.5. Scientists and researchers at DAQ will continue to comb through the data from WAFACO to identify the sources of ammonia. With better data on the sources of air pollution, DAQ can build better models. These models help inform policy decisions and assist in better regulation of pollution. Better policies and better regulation lead to better air quality.
The final report on the WAFACO study will be available to the public this fall.
Chris Pennell holds a master’s degree in atmospheric science from the University of Utah. He works as an air quality modeler for the Division of Air Quality.