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Particulate Matter Overview

Particulate matter (PM), also known as particle pollution, is a complex mixture of small solid particles and liquid droplets in the air. Some particulate matter, like soot, smoke, dust, or dirt, is large enough to see. Fine particulate matter is so small that it can only be seen through an electron microscope.

Particle pollution is produced by both primary and secondary sources. Primary particulate matter is emitted directly from construction sites, wildfires, wood burning, gravel pits, agricultural activities, and dusty roads. Secondary particulate matter is formed in the atmosphere through complex chemical reactions. PM2.5 precursors such as nitrogen oxides (NOx), volatile organic compounds (VOCs), sulfur dioxides (SO2), and ammonia contribute to the formation of secondary fine particulates. Precursors that lead to the formation of PM2.5 are emitted by a variety of sources, including power plants, industry, vehicles, small businesses, buildings, and homes.

PM10 and PM2.5

Particulate matter is divided into two categories:

Inhalable Coarse Particles (PM10)

Less than 10 microns in diameter but greater than 2.5 microns in diameter, about one-seventh the width of a human hair

Fine Particles (PM2.5 )

Less than 2.5 microns in diameter

PM concentration is measured in micrograms per cubic meter, or µg/m3.

Health and Particulate Matter

Exposure to PM10 and PM2.5 can lead to numerous health problems. Both pollutants compromise respiratory and cardiac health. Smaller particulate matter (PM2.5) poses the greatest risk because it can penetrate deeply into the lungs where it can cause inflammation and damage to the lung tissue. The health effects of particulate matter include:

  • Lung irritation, coughing, or shortness of breath
  • Worsening asthma symptoms and increased attacks
  • Increased susceptibility to respiratory infections
  • Nonfatal heart attacks and arrhythmias
  • Reduction in lung function
  • Premature death in people with lung or heart disease

Children, older adults, and those with preexisting respiratory or heart problems are at most risk from the adverse health effects of particulate pollution.

Particulate Matter Standard

The National Ambient Air Quality Standards (NAAQS) for particulate matter, first established in 1971, were based on total suspended particles (TSP) with an aerodynamic diameter of 100 micrograms per cubic meter (μg/m3) or less. Research on the health effects of TSP in the ambient air began to focus on particles small enough to be inhaled into the lungs. In 1987, EPA shifted its attention to inhalable particles equal to or smaller than 10 microns (PM10).

In July 1997, after evaluating hundreds of health studies and conducting an extensive peer-review process, EPA established PM standards that specifically addressed particles smaller than 2.5 microns (PM2.5). The annual standard was set at 15μg/m3, based on the three-year average of annual mean PM2.5 concentrations. The 24-hour standard was set at 65μg/m3 based on the three-year average of the annual 98th percentile concentrations. The 1997 standards slightly revised standards for PM10, which limited PM10 concentrations to 50μg/m3based on an annual average, and 150μg/m3 based on a 24-hour average.

EPA revised the PM standards in September 2006, lowering the level of the 24-hour PM2.5 standard to 35 μg/m3. The annual PM2.5 standard remained at 15 μg/m3, as did the 24-hour PM10 standard of 150 μg/m3. The annual PM10 standard was revoked due to the lack of evidence to establish a link between long-term exposure to coarse particles and health problems. In December, 2012, EPA reduced the annual PM2.5 standard from 15 μg/m3 to 12 μg/m3. The daily PM2.5 standard and standards for PM10 remained the same. The revised 2012 PM standard became effective in March 2013. In 2024 the EPA lowered the annual standard from 12 μg/m3 to 9.0 μg/m3 and maintained the 24-hour PM2.5 and PM10 standard at 35μg/m3 and 150μg/m3 respectively.

State Implementation Plan (SIP) Process

Within two years after setting or revising NAAQS for criteria pollutants, EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the air-quality standard. EPA’s final designations are based on the most recent three years of air-quality monitoring data, recommendations from the state, and additional technical information. State recommendations are made by the governor and take into account air-quality data, emissions, meteorology, topography, and jurisdictional boundaries.

If an area is not meeting the standard, the state is required to prepare a State Implementation Plan (SIP). The SIP is a comprehensive document that identifies how the state will attain or maintain the NAAQS to comply with the provisions of the Clean Air Act. The SIP includes regulatory and non-regulatory control measures for reaching attainment by a specific deadline.

Particulate Matter in Utah

Winter inversions are a common event in Utah, generally occurring between December and February. Prolonged inversions can lead to high levels of fine particulate pollution, or PM2.5. These high pollutant levels create significant health and air quality concerns, particularly on days when the concentrations exceed the national health standards.

Inversions occur when normal atmospheric conditions (cool air above, warm air below) invert. Inversions trap a dense layer of cold air under a layer of warm air. The warm layer acts like a lid, trapping emissions from vehicles, businesses, and industrial processes in the cold air near the valley floor. These emissions mix in this cold layer of air to form fine particulates.

There are two types of fine particulates: primary and secondary. Primary PM2.5 is emitted directly as a particle and enters the atmosphere as soot. Secondary particulates form when precursor emissions react in the atmosphere to create PM2.5. Most of Utah’s PM2.5 pollution comes from secondary particles.

Elevated PM10 concentrations in Utah tend to be localized and are generally caused by fugitive dust, particles of soil, ash, coal, minerals, etc., which becomes airborne because of wind or mechanical disturbance. Fugitive dust can be generated from natural causes such as wind or from manmade causes such as unpaved haul roads and operational areas, storage, hauling and handling of aggregate materials, construction activities and demolition activities. State rules establish minimum work practices and emission standards for sources of fugitive emissions and fugitive dust in nonattainment areas and other areas in the state. Fugitive dust rules are more stringent in PM nonattainment areas.

DAQ can implement regulatory strategies to reduce the emissions from the industrial, mobile, and area sources responsible for PM10 and PM2.5, but it cannot control certain natural events that contribute particulate matter to Utah’s air, including blowing dust from the West Desert (PM10) and wildfires (PM2.5).

For more information contact Rachel Chamberlain (rachelchamberlain@utah.gov), (801) 414-3390.

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