In recent years, Michigan has seen unprecedented levels of wildfire smoke drifting across its communities and much of the rest of the country.
In addition to pollutants like fine particulate matter carried in the smoke, there are gasses containing the chemicals that – when combined with sunlight – form ground-level ozone. These chemical reactions contribute to elevated ozone levels seen in areas across Michigan.
EGLE measures a variety of air pollutants around the State of Michigan.
Many of the monitoring sites measure particulate matter in real time and post the data to EGLE’s MiAir app and EPA’s AirNow website.
The data is communicated to the public using EPA's Air Quality Index, or AQI.
Particulate matter (PM) consists of solid particles, fine liquid droplets, or condensed liquids adsorbed onto solid particles. Particulate matter with a diameter of less than 10 microns in diameter is referred to as PM10 whereas very fine particles equal to or less than 2.5 microns 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.
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 matter is also called PM2.5. It refers to small particles that are less than 2.5 microns in diameter.
Fine particulate is especially problematic because it can penetrate deep into the lungs and remain there. 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 including burning, fugitive dust, and biogenic sources (from plants). PM2.5 can be emitted directly (primary) or chemical reactions in the air can form particles (secondary).
Additionally, 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.
A growing body of science links particle pollution to a range of serious and sometimes deadly illnesses.
Many studies show that these microscopic fine particles can penetrate deep into the lungs where they stick. Long- and short-term exposure can lead to asthma attacks, missed days of school or work, heart attacks, expensive emergency room visits and premature death.
An Advisory is called when two or more (or widespread) monitoring locations are expected to reach or exceed the Unhealthy for Sensitive Groups (USG, Orange air quality index (AQI)) threshold.
The Advisory is designed to raise awareness for those who are particularly sensitive to Fine Particulate (PM2.5), along with raising awareness for those who are not directly affected but could still take action to help lower the overall pollution levels.
An Alert is called when two or more (or widespread) monitoring locations are expected to reach or exceed the Unhealthy threshold. The Alert range is for Unhealthy (Red AQI), Very Unhealthy (Purple AQI), and Hazardous (Maroon AQI) pollution thresholds.
The Alert is designed to raise heightened awareness because all health groups are included, can be affected, and should take action to help protect themselves. The Alert is not designed to negate the AQI categories/thresholds as there is different messaging within said thresholds. The Alert will include the expected AQI Categories to help people understand forecasted pollution levels.
An advisory or alert may be called for ozone, particulate matter, or both.
The U.S. Air Quality Index (AQI) is EPA's tool for communicating about outdoor air quality and health. The AQI includes six color-coded categories, each corresponding to a range of index values. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality.
The AQI is divided into six categories. Each category corresponds to a different level of health concern. Each category also has a specific color. The color makes it easy for people to quickly determine whether air quality is reaching unhealthy levels in their communities.
The AQI includes six color-coded categories, each corresponding to a range of index values. The AQD Advisory and Alert Program Report contains information about days when advisories or alerts were called. It also contains the number of days the forecast indicated the likelihood of elevated levels of ozone, PM2.5 or both in the outdoor air.
Data from 2023 to present is included.
EGLE’s meteorologist have 13 forecasting areas used to determine where advisories and alerts should be issued.
Map of the forecasting areas That remains to be seen.
Certain data will be flagged for potential additional evaluation based on the presence of the wildfire smoke. Air monitoring data is submitted quarterly to EPA. Once all data from this year’s ozone and PM2.5 season has been collected, validated, and submitted, Michigan will analyze the results.
To pursue an exception for any data, the action must have regulatory significance – that is, the exclusion of the data must be likely to change regulatory determinations.
A decision on whether to pursue an Exceptional Events Demonstration will be decided later this year (2025) or next (2026) following analysis of all the data collected during the year (2025).
EGLE will be watching closely to see if any regulatory changes at the federal level impact Michigan.
A portion of EPA’s approval of the southeast Michigan redesignation included the acceptance of a maintenance plan that requires EGLE to continue to track emissions and air quality in southeast Michigan and take appropriate action to mitigate a trend toward lower air quality.
A possible action could include implementing additional control measures to reinforce a trend toward improving air quality.
The region’s previous “out of attainment” designation was based on the EPA’s 2015 ozone standard.
Michigan will not formally be designated as out of attainment for that standard; however there’s a maintenance plan in place to ensure appropriate action is taken in the event ozone values trend higher.
When EPA issues an updated standard the data will again be evaluated to determine attainment status.
EGLE does not have any authority to regulate wildfires in Canada. Several other agencies work with Canada on wildfires. These include:
Wildfire smoke can affect fine particulate and ozone concentrations. Many areas of the state that don’t typically see higher pollution levels have been seeing elevated pollution levels due to wildfires.
All collected data will be quality assured and validated. The validated data is then evaluated for any regulatory significance. Exceptional event demonstrations will be considered if appropriate.
The last several decades have shown decreases in fine particulate pollution across the state.
This is a result of more protective standards, technological advances, and the Energy Sector’s transition away from coal-fired power plants.
Data from some of the state's PM2.5 air monitors over time. *The NAAQS for PM2.5 was reduced to 9 ug/m3. The determination is currently under reconsideration by the EPA. 
