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 shingles


picture of peeling lead paint


Asbestos shingles


picture of peeling lead paint


picture of peeling lead paint


Vapor Intrusion Graphic

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 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.

EnviroFlash is a partnership between the US EPA and the Michigan Department of Environment, Great Lakes and Energy (EGLE). When you sign up, EnviroFlash sends air quality messages right to your inbox so you know when it’s a good time to be active outside.

Get alerts for when air quality may be harmful in your area.

Protect your health on smoky days

Check the air quality forecast

Air quality conditions may change quickly. Pay attention to local news for air quality alerts and health warnings in your area.

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.

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 FanPublic Health Insider.
  • Make a “clean air room” in your home: Learn how to keep indoor air clean on smoky daysPublic 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.

Adopted from King County, WA.

Last Modified June 20, 2024

Environmental Health
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Matt Bolang

Matt Bolang
Health Officer



(517) 546-9858


Monday – Friday
8:00 a.m. – 5:00 p.m.
Closed County Holidays


2300 E Grand River Ave
Suite 102
Howell, MI 48843


(517) 546-9853
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