Like many metropolitan areas, the Chicago area is no stranger to air pollution. That is why it is so important for Chicago area residents to understand air pollution, where it comes from, how it can affect us, and, most importantly—what we can do to prevent it. So let’s start with the basics.

Know your air quality. Get the forecast.

Just like the weather, our air quality is forecast every day because there may be elevated levels of air pollution, specifically ozone and particulate matter, which change the outdoor air quality. 

The Air Quality Index (AQI) assigns a corresponding color to the daily air quality forecast. This was set up so actions that need to be taken for each category can be quickly and effectively communicated to the public, and so that sensitive groups whose health depends on knowing can be alerted.

Get free air quality forecasts sent directly to you inbox. .

» Learn more about the Air Quality Index

Air Pollution Action Day Alerts

An Air Pollution Action Day Alert is issued when air quality data and weather conditions indicate the potential for widespread ozone or fine particulate matter levels at or above the Orange—“Unhealthy for Sensitive Groups” category on the Air Quality Index for multiple days.

As a result of the alert, individuals will know when to take necessary precaution to protect their health and to take action to further reduce contributions to air pollution.

The air quality standards were recently tightened, therefore we may see more days in the yellow/orange category this summer.

» Learn more about Air Pollution Action Day Alerts

Good ozone vs. bad ozone

Ozone is good when it is high up in the atmosphere. It protects us from ultraviolet (UV) rays that can be damaging to our skin and other living organisms. Ozone is bad when it is close to the ground where we breathe. Ground-level ozone (smog) is formed through a complex chemical reaction involving hydrocarbons, nitrogen oxides and the sunlight. High levels of ground-level ozone typically occur on hot, summer days, but can occasionally occur outside of the summer season.

» Learn more about ground-level ozone

Particulate matter

Unlike ground-level ozone, particulate matter can cause problems year-round. Particulate matter, also known as particle pollution, is made up of tiny solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot and smoke, are large enough to see with the naked eye. Others are so small, often less than one-hundredth the width of a human hair, they can only be detected using a microscope.

» Learn more about particulate matter