Air Quality Researchers Hunt for PM2.5 Precursors

By Chris Pennell

As researchers, we know a lot about air pollution. But we don’t know everything. One thing that isn’t clear is the role ammonia plays in the formation of the wintertime smog that clogs the air along the Wasatch Front.

This month, 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) got closer to solving the riddle. Researchers from these five organizations joined forces for the Wasatch Front Ammonia and Chloride Observations (WaFACO) study. The study is looking for sources of ammonia.

So why’s ammonia important? First, let’s look at what’s really in our wintertime pollution.

The technical term for Utah’s wintertime air pollution is PM2.5. PM2.5 isn’t a specific thing, it’s a measurement of any particles in the air measuring 2.5 microns or smaller. At this size, the particles are small enough to penetrate the natural barriers in our respiratory system. Once past these barriers, the particles lodge deep inside our lungs and cause all sorts of nasty health effects.

On a bad winter day, up to 70 percent of the airborne particulates measuring 2.5 microns or smaller are ammonium nitrate. 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.

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 on to 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.

Funded through a one-time appropriations from the Utah State Legislature, 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 precursors of PM2.5. For the last four weeks, 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.

In addition to the 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 gathering data at multiple locations—on the freeway at rush hour, next to farmer’s field, by landfills, and at industrial site.

Now that the collection portion of the study is done, researches will comb through the data to identify the sources of ammonia.

WaFACO comes on the heels of the 2017 multi-agency Utah Winter Fine Particulate Study (UWFPS), which examined the composition and formation mechanisms of the local wintertime particulate. One of the key findings of UWFPS study was the important role of ammonia in bad wintertime PM2.5 in the Salt Lake Valley.

We are a long way from being finished. One of our lead researchers, Randy Martin, will present some of the initial findings at Air Quality: Science for Solutions 3 in Logan on March 28.

To better inform pollution control strategies in Northern Utah, it is necessary to understand the complex chemical and physical processes that create PM2.5. Ammonium nitrate accounts for as much as 70 percent of total PM2.5 during wintertime exceedances of the federal standard. Scientists and researchers at DAQ will continue to look at the contribution and sources of the compounds to better ensure public health against air pollution along Wasatch Front.

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.