Ozone Action Day in SE Michigan: What it means

Voluntary effort to address air quality concerns


DETROIT – First of all, an Ozone Action Day means it's going to be hot and muggy.

Highs Thursday will be in the low 90s with heat indices approaching 95°F or more.

  • Thursday, July 18, 2019 is an Ozone Action Day.


The National Weather Service in Detroit/Pontiac has issued an Excessive Heat Warning, which is in effect from noon today to 8 p.m. Saturday. Temperatures will climb into the upper 80s today and then into the mid to upper 90s both Friday and Saturday. Increasing humidity will yield heat indices peaking during the afternoon hours in the 100 to 110 degree range. Low temperatures will only fall into the 70s each night limiting the possible relief from the heat.

An Excessive Heat Warning means that a prolonged period of dangerously hot temperatures will occur. The combination of hot temperatures and high humidity will combine to create a dangerous situation in which heat illnesses are likely.

In this region, the Southesast Michigan Council of Governments (SEMCOG) declares an Ozone Action Day when the weather is like this. The council says air quality is one of the important measures identified in its plans and programs.

Ozone Action days are called when hot summer temperatures are expected to combine with pollution to create high amounts of ground-level ozone. Breathing high levels of ozone can trigger a variety of health problems, particularly in children, the elderly, and people with asthma or other lung diseases.

"We all need to help keep the air clean," said Kathleen Lomako, SEMCOG Executive Director. "Since the mid-1990s, air quality in Southeast Michigan has improved. That is due, in part, to the actions that residents take on Ozone Action days, giving credence to one of SEMCOG's key messages -- that individual actions taken by many can make a difference. We look for that support again this summer."

This is the 26th year of the voluntary program. In 2018, there were nine Ozone Action days, according to SEMCOG.

This ozone infographic is provided by SEMCOG:

What you can do

Here are some things southeast Michigan residents can do to help keep the air clean:

  • Delay mowing your lawn until evening or the next day. Exhaust from your lawn mower and other gas-powered lawn and garden equipment help form ozone.
  • Leave your car at home. Instead, take the bus, carpool, bike, walk, or telecommute. You'll reduce traffic congestion and air pollution, as well as save money. Learn more about Southeast Michigan Commuter Connect.
  • Avoid refueling your vehicle during daylight hours. Fumes released at the gas pump contribute to ozone formation.
  • Delay or combine errands. This will reduce traffic congestion and air pollution.
  • Reduce electricity use. Adjust your thermostat a few degrees higher and turn off lights, computers, and other electrical devices when not in use.

Totally voluntary

There is no law that requires residents to follow these suggestions. If you really wanted to, you could go mow your lawn three times today. Your neighbors might not be so impressed, however.

Here's how the heat index works

While we're talking about heat and how the air feels, here's a quick explanation of the heat index:

The National Weather Service (NWS) explains the heat we feel outside on these hot summer days are not exactly caused by the temperature alone. You have to take into consideration the "heat index."

"The heat index is a measurement of how hot it really feels when the relative humidity is incorporated with the actual temperature," the NWS explains. "Heat indices were designed for use in the shade with light wind conditions. If in direct sunlight, the heat index can increase as much as 15 degrees. With very hot and dry air, strong winds can also be extremely dangerous."

Here's a closer look at how relative humidity and temperature combine to form the heat index and the danger levels:


Duane Friend, an Environmental and Energy Stewardship Educator with University of Illinois Extension, put together this short video explaining the heat index -- worth a watch: 

Here are four types of heat disorders that occur due to a high heat index, including their symptoms:

  • Sunburn: Redness and pain. (also swelling, blisters, fever, and headaches)
  • Heat cramps: Painful spasms usually in the legs and abdomen. (also heavy sweating)
  • Heat Exhaustion: Heavy sweating and weakness, along with cold, pale, and clammy skin.
  • Heat Stroke: A high body temperature, hot and dry skin, a rapid and strong pulse, and possible unconsciousness.

The NWS explains an Excessive Heat Warning is issued if the heat index equals or exceeds 105° for at least three consecutive hours. Heat Advisories are posted when the heat index is expected to exceed 100 degrees for three consecutive hour and can be extended into the night if low temperatures are in the 70s or higher.

The NWS suggests the following tips to stay safe during hot weather:

  • Stay out of the sun. (sunburn makes the job of heat dissipation more difficult)
  • Spend as much time as possible in air conditioning. If you do not have an air conditioner, go to an air-conditioned public building, like a library.
  • Slow down. (reduce, eliminate, or reschedule physical activities for a cooler time of the day)
  • Drink plenty of water, even if you do not feel thirsty. Do not drink any alcohol, including beer.
  • Dress in lightweight and light colored clothes. This will reflect the sunlight and heat.
  • Eat smaller meals and less proteins.
  • Do not take salt tablets unless specified by a physician.

5 heat deaths a year in Michigan

According to the NWS, Michigan averages about 5 heat related deaths each year.  

"The number of heat related illnesses are difficult to record, but it is fair to say that each year in Michigan there are hundreds of heat related illnesses some of which require hospitalizations," reads a statement by the NWS. "The national average is 134 heat related deaths making heat the number one weather related killer in the United States."

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