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Wisconsin remains under a statewide air quality advisory for fine particles from wildfire smoke through noon CT Thursday, according to the Wisconsin Department of Natural Resources.

Smoke from wildfires in Canada is spreading from north to south in what the MNR called a “highly dynamic” situation this week. The agency expects the worst impact to be from noon Tuesday to noon Wednesday.

“It is important to pay close attention to the air quality in your area and take action, especially if you are not feeling well,” the MNR said in a statement Tuesday.

The DNR and the Wisconsin Department of Health Services recommend that people of all populations limit their outdoor activities and take a break or go indoors if they are coughing and having difficulty breathing.

“Susceptible groups, including people with heart or lung conditions, the elderly, children, pregnant women and those who work outdoors, should consider moving all events indoors,” the DNR said.

Tiny, fine particles, also known as PM2.5, a major pollutant released by wildfire smoke, can “get very deep into our lungs and get into our bloodstream,” Katelyn O’Dell, a researcher at George Washington University, told the Milwaukee Journal Sentinel and Minneapolis Star Tribune.

How can you check the air quality in your area and what do the numbers mean?

The Environmental Protection Agency monitors air across the country and establishes a air quality index, or AQI.

Here's what you need to know about the index and how to monitor your area, including: US regions facing smoke from Canadian wildfires.

What does the air quality index measure?

The index measures how clean or polluted the air is each day. The EPA uses this measure to monitor five types of air pollutants. The main concern about wildfire smoke is fine particle pollution. These particles are small enough to penetrate deep into the lungs. They can cause short-term problems such as coughing and itchy eyes, and in the long term they can affect the lungs and heart.

What do the numbers and colors mean?

The index ranges from zero to 500. The higher the number, the worse the air quality. This range is divided into six color-coded categories. Green or yellow, between zero and 100, means the air is fairly clear. Once it reaches orange, air quality could become a concern for sensitive groups such as children, the elderly or people with health problems.

In red and purple zones, air quality is considered unhealthy for everyone.

As of 10 a.m. Tuesday, the air on 16th Street in Milwaukee registered a purple 223, or “very unhealthy,” according to the EPA's air quality index.

And if the index reaches brown, at 301 or higher, the contamination levels are dangerous.

At these high levels, take precautions to avoid breathing unsafe air. This may mean reducing your outdoor activities, using air purifiers indoors, and wearing a well-fitting mask like an N95 when outdoors.

“If you have to work hard, work less. Hydrate more,” said Dr. Leonardo Trasande, who studies environmental health at New York University.

What is the air like in my area?

check AirNow.govwhich is updated hourly. The site displays a real-time map of air quality across the country and also includes forecasts for the next day. The map draws measurements from a network of air monitoring stations across the country. States and cities can also offer more local guidance.