: 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
Ozone concentrates and mixes with other pollutants, turning to smog, according to the American Lung Association.
—
Maya Wilkins, Chicago Tribune, 26 May 2026
At the ground level, ozone is a harmful pollutant that is the main ingredient in smog, according to the Environmental Protection Agency.
—Neal Riley, CBS News, 19 May 2026
Outside the summit venue, Beijing’s skies were covered in thick smog with the city’s air quality index rising above 150 on Thursday, far beyond World Health Organization healthy air guidelines.
—Sujita Sinha, Interesting Engineering, 14 May 2026
The update reflects the state’s evolving understanding of its most dangerous pollutants, which has shifted over the decades from visible pollutants, such as smog, to more invisible ones that cause cancer, heart disease and other health harms.
—Los Angeles Times, 14 May 2026
See All Example Sentences for smog
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Maya Wilkins, Chicago Tribune, 26 May 2026
At the ground level, ozone is a harmful pollutant that is the main ingredient in smog, according to the Environmental Protection Agency.
—Neal Riley, CBS News, 19 May 2026
Outside the summit venue, Beijing’s skies were covered in thick smog with the city’s air quality index rising above 150 on Thursday, far beyond World Health Organization healthy air guidelines.
—Sujita Sinha, Interesting Engineering, 14 May 2026
The update reflects the state’s evolving understanding of its most dangerous pollutants, which has shifted over the decades from visible pollutants, such as smog, to more invisible ones that cause cancer, heart disease and other health harms.
—Los Angeles Times, 14 May 2026
See All Example Sentences for smog
Cite this Entry
“Smog.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/smog. Accessed 30 May. 2026.
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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