: 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
In the wake of the second World War, the relentless creep of light pollution, smog from nearby London and the vibrations and magnetic interference from railway lines had rendered Greenwich an unfeasible location for delicate astronomical observation.
—
Anthony Wood, Space.com, 22 June 2025
Opponents say the supercomputing center is stressing the power grid, and that the turbines emit smog and carbon dioxide, pollutants that cause lung irritation such as nitrogen oxides, and the carcinogen formaldehyde, experts say.
—Adrian Sainz, Los Angeles Times, 17 June 2025
Kilns are often close to densely populated areas, adding to the smog that comes from city life.
—Jonathan Lambert, NPR, 18 May 2025
Fed up with the government’s inaction, a group of residents created Polish Smog Alert, an advocacy organization pushing for legislation to suppress the smog.
—Cecilia Rodriguez, Forbes.com, 29 June 2025
See All Example Sentences for smog
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Anthony Wood, Space.com, 22 June 2025
Opponents say the supercomputing center is stressing the power grid, and that the turbines emit smog and carbon dioxide, pollutants that cause lung irritation such as nitrogen oxides, and the carcinogen formaldehyde, experts say.
—Adrian Sainz, Los Angeles Times, 17 June 2025
Kilns are often close to densely populated areas, adding to the smog that comes from city life.
—Jonathan Lambert, NPR, 18 May 2025
Fed up with the government’s inaction, a group of residents created Polish Smog Alert, an advocacy organization pushing for legislation to suppress the smog.
—Cecilia Rodriguez, Forbes.com, 29 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 19 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
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