: a fog made heavier and darker by smoke and chemical fumes
also
: a photochemical haze caused by the action of solar ultraviolet radiation on atmosphere polluted with hydrocarbons and oxides of nitrogen especially from automobile exhaust
Examples of smog in a Sentence
the city's smog was once so bad that darkness often prevailed, even at noon
Recent Examples on the Web
The state’s efforts to reduce smog in Southern California led to the use of catalytic converters and emissions treatment technology that have worked wonders in making auto exhaust much less dangerous.
—
Alan Ohnsman, Forbes.com, 16 June 2025
The pollution also creates ground-level ozone when nitrogen oxides and volatile organic compounds — emissions from vehicles — bake in the heat and form a brown smog over the Front Range.
—Noelle Phillips, Denver Post, 13 June 2025
The green house gas rating is a 9, and the smog rating is a 6, both out of 10.
—Tony Leopardo, Mercury News, 9 June 2025
By comparison, cars in the region currently emit about 9 tons of NOx per day, Martinez said.
NOx isn’t only responsible for smog.
—Hayley Smith, Los Angeles Times, 4 June 2025
See All Example Sentences for smog
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Alan Ohnsman, Forbes.com, 16 June 2025
The pollution also creates ground-level ozone when nitrogen oxides and volatile organic compounds — emissions from vehicles — bake in the heat and form a brown smog over the Front Range.
—Noelle Phillips, Denver Post, 13 June 2025
The green house gas rating is a 9, and the smog rating is a 6, both out of 10.
—Tony Leopardo, Mercury News, 9 June 2025
By comparison, cars in the region currently emit about 9 tons of NOx per day, Martinez said.
NOx isn’t only responsible for smog.
—Hayley Smith, Los Angeles Times, 4 June 2025
See All Example Sentences for smog
Cite this Entry
“Smog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/smog. Accessed 2 Jul. 2025.
Copy CitationKids Definition
smog
noun
ˈsmäg 
also ˈsmȯg
: a thick haze caused by the action of sunlight on air polluted especially by smoke and automobile exhaust fumes
Etymology
from smoke and fog
Love words? Need even more definitions?
Merriam-Webster unabridged
Share