CHICAGO (CBS) — This summer may be one of the hottest in recent memory, but it is also one of the worst for air quality.

As WBBM Newsradio’s Bernie Tafoya reports, Pollution Action Day warnings are forecast through Saturday, making the count 10 unhealthy air quality days in the Chicago area this summer.

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That figure is twice as many as last year, and more than the number of bad air quality days from last year and 2010 combined.

Kim Biggs of the Illinois Environmental Protection Agency says sizzling temperatures and ground-level ozone, emissions from cars and other factors are to blame.

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Biggs says ground level ozone is a pollutant that’s formed through a chemical reaction between sunlight and emissions in the air. In effect, the emissions are “baked by the sunlight.”

The air quality warning through Saturday is for sensitive groups – active children and adults, and people with lung problems such as asthma. Advice is not to overdo it outside.

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LISTEN: WBBM Newsradio’s Bernie Tafoya reports