: 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
Gasification primarily served local smog control goals rather than a reduction in coal infrastructure.
—
Wesley Alexander Hill, Forbes.com, 11 Aug. 2025
In 1970, when a nearly unanimous Congress approved sweeping changes strengthening federal air pollution laws, one proviso allowed California in many cases to craft its own rules — a recognition of the challenge the Golden State faced in dealing with the nation’s worst smog problem.
—U T Editorial Board, San Diego Union-Tribune, 11 July 2025
As a result, Rybnik experienced just 16 smog days in 2023.
—Skylar Knight, Smithsonian Magazine, 27 June 2025
The air has long since been cleaned up from the smog of the 1960s, so now the government of California is fully focused on degrading the quality of life.
—Susan Shelley, Oc Register, 19 June 2025
See All Example Sentences for smog
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Wesley Alexander Hill, Forbes.com, 11 Aug. 2025
In 1970, when a nearly unanimous Congress approved sweeping changes strengthening federal air pollution laws, one proviso allowed California in many cases to craft its own rules — a recognition of the challenge the Golden State faced in dealing with the nation’s worst smog problem.
—U T Editorial Board, San Diego Union-Tribune, 11 July 2025
As a result, Rybnik experienced just 16 smog days in 2023.
—Skylar Knight, Smithsonian Magazine, 27 June 2025
The air has long since been cleaned up from the smog of the 1960s, so now the government of California is fully focused on degrading the quality of life.
—Susan Shelley, Oc Register, 19 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 21 Aug. 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
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