At O'Hare International Airport, officials enacted a ground stop for all flights arriving between 7 a.m. and 9 p.m. because of the fog and say the average arrival delays were more than 100 minutes as of 6:30 a.m. Tuesday. Midway is not experiencing the same problems.
Visibility at O'Hare improved to one mile as of 8:30 a.m., but out in Gurnee it was still basically zero at that time.
Drivers at the O'Hare Oasis were struggling to make it to their destinations.
"It's just amazing out there. It's so thick. On the expressway, you thought it would lighten up. But it didn't," said driver Brad Rybicki.
"You have to slow down. You have to always look at the cars before you, and you have to be always careful, that's how it is," said driver Salaman Abdullah.
"I've been here an hour waiting on my daughter to come in. I started picking it up at the 19 Mile Marker in Indiana at the Bass Pro, and it just kept getting worse as we got here," said driver Martin Kurtz.
Tuesday is also an air-pollution action day.