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Background
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. These particles are so small that they can become imbedded in human lung tissue, causing or exacerbating respiratory diseases and cardiovascular problems. Other negative effects are reduced visibility and accelerated deterioration of buildings.
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.
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), which are 2.5 micrometers in diameter and smaller; and inhalable coarse particles (PM10), which are smaller than 10 micrometers. 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. 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.
It proposes that there are three areas within the state that should be designated as nonattainment for PM2.5. These areas are as follows:
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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. Figure 1 shows the sources of direct PM emissions along the Wasatch Front.
During winter temperature inversions when we have historically exceeded the national standards, we find the majority of our PM is composed of particles that have formed from chemical reactions in the air. These particles include acids such as nitrates and sulfates, and organic chemicals. Figure 2 shows the sources of nitrates and sulfates along the Wasatch Front.
PM10Status
When thePM10 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. 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 are were attaining the 1997 PM2.5 NAAQS. However, now that the 24-hr standard has been lowered from 65 µg/m3 to 35 µg/m3 , many of our urban areas will find themselves out of compliance of the 24-hour PM2.5 NAAQS. Utah is presently in the process of designating areas within the State as either attaining or not attaining this new NAAQS. See the blue box above for details.
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.
PM10 air trend plots:
PM2.5 Trends
We have been collecting PM2.5 data 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:
Following promulgation of a new or revised standard, the CAA (section 107(d)) allows States the opportunity to provide their recommendations to EPA, concerning area designations, prior to any final action taken by EPA. Utah submitted its recommendations to EPA on December 18, 2007 in a document titled "
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