air pollution by a mixture of smoke and fog
"The morning commute was impossible because thick smog from factory smoke mixed with heavy fog had blanketed the city."
A noxious mixture of particulates and gases that is the result of urban air pollution.
"The thick smog choking the city made it difficult to see more than a few blocks ahead."
To get a smog check; to check a vehicle or have it checked for emissions.
"Before selling my old car, I took it in to get a smog check so we could verify that the emissions were within legal limits."