Particulates (PM10, PM 2.5)

Contact: Air Quality Related Issues: Robert Irvine, 517-648-7367
Agency: Environment, Great Lakes, and Energy

Particulate matter consists of solid particles, fine liquid droplets, or condensed liquids adsorbed onto solid particles. Particulate with a diameter of less than 10 micrometers in diameter is referred to as PM10 whereas very fine particles equal to or less than 2.5 micrometers in diameter is referred to as PM2.5.

Particulate emissions are primarily composed of smoke, dust, dirt, soot, fly ash, and condensing vapors. The particles or droplets are composed of different elements depending on the emission source. Chemical reactions can occur in the atmosphere and form new chemical compounds or change the form from gases and liquids into solid particles. 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.

Annual average PM10 levels over the decade have remained at nearly one-half of the standard. Michigan has been designated as being in attainment with the PM10 particulate National Ambient Air Quality Standard (NAAQS) since October 4, 1996.

The USEPA established a new standard for very fine particles (2.5 micrometers or less), which are a particular concern for lung and cardiovascular effects. Annual arithmetic mean not to exceed 15 micrograms per cubic meter (µg/m3) (based on a three-year average); or 98th percentile of 24-hour concentration not to exceed 35 µg/m3 (based on a three-year average). Under the Clean Air Act, those areas that violate the NAAQS, or are nearby and contribute to a violation, are considered "nonattainment."

Fine particulate matter (PM2.5) is tiny liquid or solid particles with a diameter less then 2.5 micrometers. PM2.5 is composed mainly of ammonium sulfate, ammonium nitrate, organic carbon, and smaller portions from elemental carbon and soil or crustal elements. PM2.5 comes from a variety of sources included burning, fugitive dust, and biogenic sources (from plants). PM2.5 can be emitted directly (primary) or react in the air to form particles (secondary). Respiratory and cardiac problems are directly linked to PM2.5 exposure. Children, older adults and people with heart or lung diseases are especially susceptible to the health effects from PM2.5. In 2006, the EPA maintained the annual standard at 15 µg/m3 and revised the NAAQS PM2.5 24 hour by reducing it to 35 µg/m3. The EPA designated seven counties in the Detroit-Ann Arbor Metropolitan Statistical Area (Southeast Michigan) as nonattainment for the annual and 24-hour PM2.5 NAAQS: Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw, and Wayne counties. Air quality monitoring data collected in the 2007 - 2010 period showed all seven counties in Southeast Michigan in attainment for the PM2.5 annual and daily NAAQS.

Particulate matter can affect breathing and the defenses of the lungs, and aggravates existing respiratory and heart disease. More serious effects may occur depending on the length of exposure, the concentration, and the chemical nature of the particulate matter. Asthmatics and individuals with chronic lung and/or heart disease, people with influenza, the elderly, and children are the most susceptible. Fine particulate is especially problematic because it can penetrate deep into the lungs and remain there.

Particulate matter is the major cause of reduced visibility in many parts of the United States. PM2.5 is considered to be an important visibility-reducing component of urban and regional haze. Airborne particles can also impact vegetation and ecosystems and can cause damage to paints, building materials and/or surfaces. Deposition of acid aerosols and salts may increase corrosion of metals and impact plant tissue by corroding leaf surfaces and interfering with plant metabolism.