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Clean Air Action Days and National Clean Air Day

June 11, 2025

By: Erin Parker, Interpretive Services Supervisor

Air quality alerts and ozone actions days seem to come more frequently and earlier in the spring every year. While they are caused by different sources and environmental conditions, both mean that breathing outdoor air can pose a hazard. Let’s explore the differences, similarities, and actions we can take to reduce our exposure to dangerous conditions.

Ozone and Clean Air Action Days

What is ozone? Ozone is a molecule made up of three atoms of oxygen. Depending on where ozone is located, it can be beneficial or harmful. Ozone in the upper layers of our atmosphere helps to protect us from UV radiation from the sun. Unfortunately, ozone at ground level causes smog and makes breathing difficult and dangerous for many people.

Ozone is formed through natural reactions of heat and sunlight with different compounds and molecules. In the upper atmosphere, radiation from the sun interacts with O2 (the stable, more common form of oxygen). But down on the ground, compounds released from fossil fuel combustion such as car exhaust react with sunlight and heat to create ground-level ozone.

Hot summer days in highly industrial or urbanized settings, where smoke, exhaust, and other volatile organic compounds are concentrated, are where ozone levels may reach unhealthy levels. “Ozone season” in Michigan is considered to run from March 1 to September 30th each year. In Michigan, if ground-level ozone reaches 70 parts per billion (ppb) it triggers a Clean Air Action Day.

During Clean Air Action Days, people with respiratory conditions, including asthma, are at increased risk of harm just from the air quality around them. But these days aren’t just a hazard for people with respiratory concerns, they’re also dangerous for people that work or exercise outside.  Formerly known as Ozone Action Days, Clean Air Action Days have expanded to also incorporate alerts for poor air quality due to particulate matter from things like wildfire smoke.

At the Metroparks, when the conditions are right for ground-level ozone formation, mowing and other exhaust-creating activities are done early in the day before the heat of the day. Long-term, moving to electric vehicles and equipment is helping to reduce the amount of ozone-creating exhaust.

Air Quality Index

Everyone benefits from good air quality- whether you have a respiratory condition, work outdoors, or simply enjoy being outside in the summer. But how do you know when air conditions have become less than ideal and what the impacts on your health might be?
That’s where the air quality index comes in to provide guidance on who and what activities might be impacted on a given day.

The Air Quality Index is used to communicate about air quality conditions and for short-term forecasts about air quality conditions in the near future.

The Air Quality Index, designed by the Environmental Protection Agency (EPA), is a simple color-coded tool to help the EPA communicate about the risks of air quality. Running on an index from “under 50= good air quality” to “above 301= hazardous”, the index bases air quality warnings on the presence and/or levels of five different types of air pollutants:

  • ground-level ozone
  • particulates
  • carbon monoxide
  • sulfur dioxide
  • nitrogen dioxide
Smoke from wildfires in Canada caused haze and a poor air quality rating in June of 2023 while these teachers take quick observations during a workshop at Lake St Clair Metropark. On poor air quality days such as this one, people are encouraged to keep their time outside short.

The Air Quality Index uses familiar color schemes to help quickly communicate risk levels in a particular place. For example, green indicates good air quality while dark maroon is the color of the highest levels of air pollutants. Because weather, temperature, and sunlight play such an important role in the formation and levels of many air pollutants, an Air Quality Index forecast is often shared for the upcoming day or days- allowing people, schools, and organizations to make informed decisions about their activities and risk.

National Clean Air Day

National Clean Air Day takes place on the third Thursday in June, which in 2025 is June 19th. Designed to draw awareness to issues of air quality and health, through education and action steps that reduce air pollution.

While there are many steps that organizations, communities, and individuals can do to reduce air pollution, such as reducing emissions from vehicles and factories, the Metroparks and other green spaces play one important role simply by existing. Green spaces and trees provide shade, filter the air, and absorb pollutants. All of these contribute to better air quality for park visitors, wildlife, and local communities.

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