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Statewide particulate matter trending down

July 25, 2019

Chart showing 10-year trend of statewide particulate matter

When it comes to particulate emissions, it appears Michigan is headed in the right direction. Over the past 10 years, Michigan's annual ambient particulate matter concentrations have been trending downward. Air monitors show concentrations are below federal standards throughout Michigan, in some areas by a large margin.

Particulate matter emissions are primarily composed of smoke, dust, dirt, soot, fly ash, and condensing vapors. Industrial processes that cause these emissions include combustion, incineration, construction, mining, metal smelting, metal processing, and grinding. Non-industrial sources include motor vehicle exhaust, road dust, wind-blown soil, forest fires, volcanic activity, and farm operations.

Particulate matter is divided into multiple subcategories for, among other things, regulatory purposes. Particulate matter with a diameter of less than 10 micrometers in diameter is referred to as PM10. Very fine particulate matter equal to or less than 2.5 micrometers in diameter is referred to as PM2.5. Respiratory and cardiac problems can be directly linked to PM2.5 exposure.

Air monitors throughout the state measure concentrations of PM2.5 and PM10. The Michigan Department of Environment, Great Lakes, and Energy’s (EGLE) Air Quality Division (AQD) staff calculate the three-year average and compare these values to the National Ambient Air Quality Standards (NAAQS), set by the United States Environmental Protection Agency (USEPA). The USEPA has set the NAAQS to be protective of even the most sensitive groups of people, such as children, the elderly, and those with existing lung conditions. This information is also used to determine an area’s attainment status. Being in attainment means an area is below the NAAQS for that pollutant.

  • Michigan has been designated as being in attainment with the PM10 NAAQS since 1996 and continues to be around half of the 150 micrograms per cubic meter (µg/m3) standard.
  • In 1997, the USEPA established an annual PM2.5 NAAQS of 15 µg/m3 and a 24-hour standard of 65 µg/m3. In 2006, the 24-hour PM2.5 NAAQS was lowered to 35 µg/m3. Later, in 2012, the USEPA revised the primary annual PM2.5 NAAQS by reducing it to 12 µg/m3 while the 24-hour standard remained unchanged.
  • Michigan was determined to be in nonattainment status for the 1997 and 2006 PM2.5 standards but was redesignated to attainment in 2013, and has always been in attainment with the 2012 NAAQS.
  • Monitoring data shows slightly higher PM2.5 in east Michigan than in west Michigan, with the lowest in northern Michigan.

It is believed several factors may be contributing to improving outdoor particulate concentrations over the past several years. Continued pollution prevention and reduction efforts by manufacturers and cleaner motor vehicles may explain some improvements. Additionally, a shift in many industries away from "dirtier" fuels like coal and diesel to natural gas, such as in electric generation, could be a big reason for the positive trends.

Based on the recent history and trends in electrical generation and motor vehicles, we expect particulate matter concentrations in the outdoor air to continue to decrease. EGLE's AQD will maintain our program to monitor these concentrations with respect to the NAAQS to continue to be protective of human health and the environment.

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