Dense smoke from wildfires burning in Canada will once again impact skies in northeast Illinois and northwest Indiana, with an air quality alert in effect Thursday for the entire Chicago area.
The poor air quality is expected to last at least until midnight, the NBC 5 Storm Team said.
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WATCH HERE"All day today, all the way through midnight," NBC 5 Storm Team Meteorologist Kevin Jeanes said. "There's a chance that gets extended into tomorrow."
As of early Thursday, the air quality for much of northeast Illinois, including multiple suburbs to the north and some to the west, fell into the "unhealthy for sensitive groups" category, which ranks as level two on a scale of six. In other parts of the Chicago area however, the air quality was even worse, ranking at level three.
That poor air quality was also mixing with fog, Jeanes said, creating some lower visibility.
"Some sensors are reading 'unhealthy' for everyone, not just sensitive groups," Jeanes said. Those readings were mostly in Chicago, as well areas in and near northwest Indiana.
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A real-time, interactive map of air quality from AirNow.gov can be found below:
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SIGN UP Though skies will be hazy, it's hard to tell how close to the surface the smoke will get.
"We may smell a bit of smoke in the air today and tonight," Jeanes said.
The poor air quality also led the Illinois Environmental Protection Agency to declare an "Air Pollution Action Day" for the entire Chicago area, which are issued when widespread ozone or particulate levels are at or above the "unhealthy for sensitive groups" category for multiple days.
"Active children and adults, especially people with pulmonary or respiratory disease such as asthma, should limit prolonged outdoor activity," the National Weather Service warned.
The Illinois EPA also encouraged residents to avoid filling up cars with gas until after sunset, and grouping errands to minimize the number of trips taken. Carpooling and use of public transit are also highly encouraged on high pollution days, the EPA said.
Temperatures Thursday would be in the mid 70s inland, with cooler readings near the lakefront. Temperatures will remain in the 70s through the weekend and into early next week, Jeanes said, with highs in the 80s beginning Wednesday.
What is the Air Quality Index?
According to officials, the Air Quality Index, or the AQI, is used by the Environmental Protection Agency to communicate to the public air quality levels, and how they can impact day-to-day life.
There are six different levels of air quality, and they’re all color-coded to illustrate changes in quality and how they impact residents.
Typically, anything above 100 is considered to be hazardous to at least some groups, and anything over 150 is considered to be “unhealthy,” posing issues to the general public.
How to find Chicago's AQI
AirNow provides a tool for residents to search their ZIP code to see what their forecasted air quality is, both in real time and for the days ahead.
For a more granular look, the website also offers information on different measurement stations around the area in real-time, allowing residents to track air quality in areas near their homes.
Early Thursday morning, Chicago's AQI, with a PM2.5 of 160, was listed in the "unhealthy" category.
What is PM2.5?
According to the Environmental Protection Agency, "PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air."
"Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope," the EPA states.
PM2.5 in particular involves "fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller." By comparison, the average human hair strand is about 70 micrometers in diameter, or 30 times larger than these particles.
PM2.5 is one of five major air pollutants regulated by the Clean Air Act, which also includes ground-level ozone, carbon monoxide, sulfur dioxide and nitrogen dioxide.
