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Particulate Matter


Particulate matter (PM), also known as particle pollution, is a complex mixture of extremely small dust and soot particles. PM is divided into two categories, “PM10” and “PM2.5.” PM10 is matter 10 micrometers in diameter or less. That would be about one-seventh the width of a strand of human hair. PM2.5 is even smaller—measuring 2.5 micrometers or less.

PM concentration is reported in micrograms per cubic meter, or µg/m3. The particulate is collected on a filter and weighed. This weight is combined with the known amount of air that passed through the filter to determine the concentration in the air.

The EPA revised the National Ambient Air Quality Standards (NAAQS) for PM pollution on September 21, 2006. The final standards address two categories of particle pollution:

  • Fine Particles (PM2.5)
    2.5 micrometers in diameter and smaller.

  • Inhalable Coarse Particles (PM10)
    Smaller than 10 micrometers.

The EPA strengthened the 24-hour PM2.5standard from the 1997 level of 65 µg/m3 to 35 µg/m3, and retained the current annual PM2.5 standard at 15 μg/m3. The EPA also retained the existing national 24-hour PM10 standard of 150 µg/m3; however, it revoked the annual PM10 standard. These new standards went into effect on December 18, 2006. 

The effective date for the area designations was December 14, 2009. Utah was required to submit State Implementation Plans for these areas by December 14, 2012, three years from the effective date. Many other significant deadlines concerning the administration of the 2006 PM2.5 health standards will be measured from that effective date.

Particle pollution is made up of a number of components. Soil and dust particles and certain metals are emitted directly into the air as PM. The primary human-caused sources of PM include blowing dust from construction sites and agricultural activities, as well as combustion products from solid fuels. In Utah, elevated levels of PM can also occur when dust blows off the west desert. A chart shows the sources of direct PM emissions along the Wasatch Front.

During winter temperature inversions, when the Wasatch Front has historically exceeded the national standards, a majority of the PM is composed of particles that have formed from chemical reactions in the air. These particles include organic chemicals and acids, such as nitrates and sulfates. A chart shows the sources of nitrates and sulfates along the Wasatch Front.

Particulate Matter Standard Status

PM10Status

When the PM10 standard was first established, Utah was unable to meet it. The State Implementation Plans for Utah and Salt Lake Counties in 1991 added control measures for industries including smelters, refineries and power plants, and some industries were required to burn natural gas instead of coal during the winter inversion season. A wood-burning restriction program also was added at that time, and improvements were made in the vehicle emissions inspection and maintenance program. The EPA approved those SIPs in 1994, and both areas have been in compliance with the NAAQS since 1996. In 2005, Utah completedPM10 maintenance plans for all areas showing that they expect to remain in compliance for the next 10 years; the plans have been submitted to EPA.

PM2.5Status

All areas of Utah were attaining the 1997 PM2.5 NAAQS. However, now that the 24-hour standard has been lowered from 65 µg/m3 to 35 µg/m3 , many of our urban areas have been designated nonattainment areas. See a map of these areas.

Particulate Matter Trends

PM10Trends

For PM10, most high values tend to occur during wintertime inversions. In the summertime high wind events can also lead to unusually high PM10 values. Trends are somewhat difficult to evaluate because weather plays such a large role in the data collected from year-to-year. This is why the standard is evaluated over a three year period. The fluctuations in this chart reflect the variability produced by meteorology and high-wind events.

PM10 Air Trend Plots

The fluctuations in this chart reflect the variability produced by meteorology and high-wind events.

  • See a chart of the highest PM10 24-hr concentrations recorded from 1990- 2011. This reflects control measures implemented through the PM10 SIP between 1992-94. Controls were directed at reducing high concentrations typically recorded during wintertime inversions. Much of the PM10 that was controlled was secondary PM and would have been measured as PM2.5.
  • See a chart of the PM10 annual mean concentration calculated by using values from 1990-2009. The EPA revoked the annual PM10 standard in 2006 (effective December 18, 2006), nevertheless, this is still a good indicator of long-term trends.

PM2.5 Trends

PM2.5 data has been collected at most monitoring stations since 2000. Like PM10, maximum values also tend to occur during wintertime inversions. Also like PM10, trends are somewhat difficult to evaluate because weather plays such a large role in the data collected from year-to-year. This is why the standard is evaluated over a three year period.

PM2.5 Air Trend Plots

For more information contact Bill Reiss (801) 536-4077.