: 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 New Haven, Hartford, Waterbury metro area continued to post failing grades for ozone smog but showed improvements in particle pollution, according to the report.
—
Livi Stanford, Hartford Courant, 28 Apr. 2026
Fifty years ago, a teen at a summer mountain camp learned about smog in Southern California and its effects on forests.
—Joy Benedict, CBS News, 23 Apr. 2026
The report analyzes data from 2022 through 2024 to grade counties on unhealthy levels of ozone and particle pollution, or smog and soot.
—Samantha Neely, USA Today, 23 Apr. 2026
Ozone pollution, also called smog, is the presence of ground-level ozone that forms when chemicals like nitrogen oxides and volatile organics from electric utilities, car exhaust, gasoline vapors, industrial facilities and chemical solvents react to sunlight.
—Jen Christensen, CNN Money, 22 Apr. 2026
See All Example Sentences for smog
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Livi Stanford, Hartford Courant, 28 Apr. 2026
Fifty years ago, a teen at a summer mountain camp learned about smog in Southern California and its effects on forests.
—Joy Benedict, CBS News, 23 Apr. 2026
The report analyzes data from 2022 through 2024 to grade counties on unhealthy levels of ozone and particle pollution, or smog and soot.
—Samantha Neely, USA Today, 23 Apr. 2026
Ozone pollution, also called smog, is the presence of ground-level ozone that forms when chemicals like nitrogen oxides and volatile organics from electric utilities, car exhaust, gasoline vapors, industrial facilities and chemical solvents react to sunlight.
—Jen Christensen, CNN Money, 22 Apr. 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 2 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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