Air Quality
Indoor Air
Indoor air pollution can affect your health.
Outdoor Air
Protect your health on poor air quality days.
Indoor Air
Many of us spend a majority of our day indoors either in schools, workplaces or home. As such, a healthy indoor environment is vital for healthy living. The Environmental Protection Agency (EPA) estimates that people spend 90% of a typical day indoors. Many pollutants are two to five times higher indoors than outdoors.
Indoor air pollution can have significant effects on your health. Please review the information below to help keep your home and surroundings safe and healthy.
Asbestos
Lead
Mercury
Mold
Radon
Vapor Intrusion
Healthy indoor spaces are key to reducing the spread of airborne diseases, including viruses. Two key strategies to improve indoor air include ventilation and filtration:
- Ventilation pulls fresh outside air into indoor spaces to reduce the amount of airborne pollutants, such as viruses.
- Filtration removes viruses and pollutants from the air by trapping them in a filter.
Air Filters
Air cleaners and HVAC filters are designed to filter pollutants or contaminants out of the air that passes through them. Air cleaning and filtration can help reduce airborne contaminants, including particles containing viruses.
HEPA is a type of pleated mechanical air filter. It is an acronym for “high efficiency particulate air [filter]”. This type of air filter can remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns corresponds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst case particle size results in the worst case efficiency rating (i.e., 99.97% or better for all particle sizes).
All air cleaners need periodic cleaning and filter replacement to function properly. Follow manufacturer’s recommendations on maintenance and replacement.
Minimum Efficiency Reporting Values, or MERVs, report a filter’s ability to capture larger particles between 0.3 and 10 microns (µm).
- This value is helpful in comparing the performance of different filters.
- The higher the MERV rating, the better the filter is at trapping specific types of particles.
Legionella
Legionella bacteria are found naturally in freshwater environments, like lakes and streams. The bacteria can become a health concern when they grow and spread in human-made building water systems. Legionella bacteria can cause a serious type of pneumonia (lung infection) called Legionnaires’ disease. There are no vaccines that can prevent Legionnaires’ disease. Instead, the key to preventing Legionnaires’ disease is to reduce the risk of Legionella growth and spread.
Building owners and managers can use a water management program to reduce the risk of Legionella growing and spreading. Building water systems and devices that might grow and spread Legionella include:
- Showerheads and sink faucets
- Cooling towers (structures that contain water and a fan as part of centralized air cooling systems for buildings or industrial processes)
- Hot tubs
- Decorative fountains and water features
- Hot water tanks and heaters
- Large, complex plumbing systems
The LCHD Environmental Health Division will respond to cases of Legionnaires’ disease by investigating potential sources within a water supply system of a hospital, larger office building, or certain residential communities.
Check out the CDC’s Legionnaire fact sheet for more information.
Outdoor Air
Air pollution can compromise human health and the environment in many ways. For example, outdoor air pollution:
- Is associated with many human health effects including heart attacks, asthma attacks, bronchitis, and premature mortality.
- Can contribute to what is commonly known as “acid rain.”
- Can impair visibility and damage crops and surfaces of treasured buildings and monuments.
- Can diminish the protective ozone layer in the upper atmosphere.
Wildfire Smoke and Air Quality
EnviroFlash AirNow sends air quality messages right to your inbox. Sign up to get alerts for when air quality may be harmful in your area.
Health Effects of Wildfire Smoke
Wildfire smoke is made up of gases and small (or fine) particles that can harm your health if you breathe it. The health effects can range from stinging eyes, wheezing, coughing and shortness of breath. Serious health effects can include triggering of asthma attacks and heart failure that can lead to premature death.
Everyone should avoid breathing wildfire smoke, but some people are more sensitive to it because of their age or pre-existing health conditions. People with heart or lung disease, older adults, children, and teens, pregnant people and outdoor workers may be more susceptible to the impacts of wildfire smoke.
Learn more about what’s in wildfire smoke at the Environmental Protection Agency’s (EPA) page, “Wildfire Smoke – A Complex Mixture.”
Protect your Health on Smoky Days
Check the air quality forecast
Air quality conditions may change quickly. Check AirNow to monitor air quality conditions throughout the day. Pay attention to local news for air quality alerts and health warnings in your area or sign up for air quality alerts.
Limit physical activity outdoors
Limit exercise and vigorous physical activity outdoors when smoke levels are “unhealthy for sensitive groups” or worse (101+ AQI). This includes physical labor, running, biking, and sports.
Adjust your level of physical activity according to MDHHS’s Your Health and Wildfire Smoke guidance.
Stay indoors as much as possible, and make plans for indoor activities for kids on smoky days
Move indoors if you can, and keep the air inside air clean. If you can’t move indoors, an N95 mask offers good protection from wildfire smoke for most people.
Consider what your children can do if they need to stay indoors when smoke levels are “unhealthy for sensitive groups” or worse. Some examples: dance party, karaoke, board games and puzzles, making friendship bracelets, obstacle course, indoor cornhole tournament, and movies.
Keep indoor air clean
- Close windows and doors as much as possible. If it becomes too hot, open the windows to cool down the space, or move to a mall, library, or other air-conditioned building.
- Use fans or an air conditioner (AC) when it’s hot, if possible. Set your AC to recirculate.
- Use an air cleaner with a HEPA filter if possible. More information: EPA’s Indoor Air Filtration Factsheet.
- A DIY air filter fan may be an easy and cost-effective way to clean air inside your home. Learn how to make a quick air filter with a box fan, a MERV-13 filter and duct tape: Public Health Crafter’s Corner: 1-minute DIY Filter Fan, Public Health Insider.
- Make a “clean air room” in your home: Learn how to keep indoor air clean on smoky days, Public Health Insider.
- Don’t smoke, use candles, or vacuum – these activities pollute indoor air. Avoid frying and broiling when cooking indoors.
Watch for symptoms of smoke exposure
Move someone inside if they have a headache, sore throat, cough, burning or watery eyes, dizziness, or wheezing. If you have asthma or another respiratory or heart condition, keep inhalers and medications ready and make a plan with your healthcare provider.
Call 911 if someone has shortness of breath or chest pain. You can also send a text to 911 if you are deaf, hard of hearing, or speech impaired.
Information adapted from King County, WA.
MDHHS Wildfire Smoke Guidance
Air Quality Index (AQI) Guidance
The Air Quality Index (AQI) can help you to make decisions about how to protect your health at different levels of air pollution. View full MDHHS guidelines at bit.ly/MichiganGuideForAQI.
Green (Good, 0-15)
- Everyone can enjoy being outside.
Yellow (Moderate, 51-100)
- Most people can enjoy being outside.
Orange (Unhealthy for Sensitive Groups, 101-150)
- High-risk people should make outdoor activities shorter and less intense.
- Close windows; use MERV‑13+ filters or portable air cleaners.
Red (Unhealthy, 151-200)
- Everyone should reduce long or intense outdoor activities.
- Sensitive groups should stay indoors with cleaner air.
- Close windows; use MERV‑13+ filters or portable air cleaners.
- Consider moving portions of outdoor events indoors.
Purple (Very Unhealthy, 201-300)
- Everyone should avoid long or intense outdoor activities; move activities indoors.
- Sensitive groups should keep activity levels low and stay in clean-air spaces.
- Masks (N95/P100) are recommended for anyone outdoors.
- Reschedule or move all outdoor activities indoors, if possible.
Maroon (Hazardous, 300+)
- Everyone should stay indoors in clean air and keep activity levels low.
- Create “clean-air rooms” using HEPA or DIY air cleaners.
- If home air quality cannot be maintained, seek temporary shelter or cooling centers.
- Reschedule or move all outdoor activities indoors.
School, Childcare, and Camp Guidance
Review the air quality guide for modifying youth activities.
- Modify or cancel outdoor activities depending on AQI level.
- Use portable air cleaners in classrooms/cabins/etc. without adequate HVAC filtration.
- Monitor children closely for symptoms during any outdoor activity.
- Consider school closures if smoke levels are high and buildings lack air conditioning.
Outdoor Events
- Check AQI frequently using AirNow.gov; smoke levels can change quickly.
- Prepare indoor backup plans with adequate ventilation and air filtration.
- Communicate updates to attendees through email, social media, or signage.
- Support sensitive groups by offering indoor clean‑air spaces and encouraging mask use.
- Provide N95s, hydration stations, and avoid smoke‑producing activities like grilling or bonfires.
- AQI-specific Recommendations:
- AQI 151–200 (Unhealthy): Reduce strenuous outdoor activities; consider moving portions of the event indoors.
- AQI 201–300 (Very Unhealthy): Strongly consider relocating the event indoors; provide N95 respirators if outdoors.
- AQI 300+ (Hazardous): Postpone or cancel outdoor events; only hold activities in clean, filtered indoor air.
Worker Safety
- If possible, provide alternative indoor work opportunities for outdoor workers.
- If outdoor work cannot be avoided, workers should reduce strenuous tasks, take frequent breaks indoors, and use appropriate mask/respiratory protection.
- Employers can consult OSHA guidance for wildfire smoke protections.
- Contact MiOSHA for more information or to file a complaint.
Last Modified July 17, 2026
