3A: Northern Utah’s fine particulate matter (PM2.5)

Randal Martin | Chapter Three: Air

TAKEAWAY

PM2.5 remains an ongoing and complex problem in northern Utah, but we have shown we can effectively reduce wintertime PM2.5 in Cache Valley and address attainment challenges along the Wasatch Front.

PM2.5 has been the most problematic wintertime haze-causing pollutant along the Wasatch Front and Cache Valley over the past 20 years. Through several years of cooperative research, public awareness, and regulatory programs, PM2.5 reduction programs are somewhat a success story. Figure 3A.1 shows that there has been a general decrease in northern Utah’s PM2.5, particularly since 2013, when implementation plans were put into place. As can also be seen, the PM2.5 decreases occurred even though the region’s population increased linearly (approximately two percent each year).

The formerly “moderate” nonattainment Cache Valley airshed reached attainment goals and was officially redesignated to “maintenance” in June 2021. Although recent data suggests that the Provo and Salt Lake City airsheds may have obtained their three-year averaged attainment goals, uncertainties and complexities in the understanding of emissions and photochemical mechanisms have caused the entire Wasatch Front airshed to be designated by the U.S. EPA as “serious” nonattainment.

Outlook

The future of Utah’s PM2.5 management, at least for the next 10-20 years, will require the state to maintain attainment status where it has been achieved and demonstrate that sufficient plans will be implemented in the near term to effectively reduce PM2.5 as soon as possible where exceedances are still observed. With Utah’s continued growth, mostly in metropolitan areas, this could be a challenge, and it will require further understanding of other potential proactive minimization strategies. A multi-agency and multi-university study is tentatively planned for the winter of 2023-24. Figure 3A.1 also shows the potential, unfortunately, that the PM2.5 concentrations in several airsheds may be trending upwards in the last few years. Exceedances, and redesignation as nonattainment, could be only a bad winter away.

Line graph of 98th percentile 24-hour PM₂.₅ measured in micrograms per cubic meter from 2002 to 2020. The vertical axis values range from 0 micrograms per cubic meter to 110 micrograms per cubic meter. Seven lines represent PM₂.₅ in the areas Cache Valley, Bountiful, Lindon, Ogden, Rose Park, Harrisville, and Hawthorne respectively. These lines follow the same general trends of increases and decreases, including a spike in 98th percentile 24-hour PM₂.₅ in the years 2004, 2007, and 2013. An additional line indicates 24-hour NAAQS, which stayed at about 65 micrograms per cubic meter until 2006, when it dropped to around 35 micrograms per cubic meter. 24-hour NAAQS has remained at this level since 2006. Overlaid on the 98th percentile 24-hour PM₂.₅ line graph is an additional line graph with a single line representing Wasatch Front and Cache County population in thousands. The vertical axis for this graph ranges from 1800 thousand to 2800 thousand. The line on this graph shows a constant growth in population from about 1900 thousand in 2002 to about 2700 thousand in 2020.