: 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 agency is closing the Office of Research and Development, which analyzes dangers posed by a variety of hazards, including toxic chemicals, climate change, smog, wildfires, indoor air contaminants, water pollution, watershed destruction and drinking water pollutants.
—
Rob Stein, NPR, 20 July 2025
What is causing poor air quality in Phoenix? Phoenix’s poor air quality stems from a potent combination of smog, particle pollution and dust, exacerbated by our hot desert climate and human activity.
—Tiffany Acosta, AZCentral.com, 1 July 2025
Last year, the court upended a Biden administration effort to reduce smog and air pollution wafting across state lines.
—Cnn, Mercury News, 20 June 2025
The turbines emit nitrogen oxides, a key contributor to smog, and formaldehyde, among other pollutants, according to their manufacturer.
—Bracey Harris, NBC news, 17 June 2025
See All Example Sentences for smog
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Rob Stein, NPR, 20 July 2025
What is causing poor air quality in Phoenix? Phoenix’s poor air quality stems from a potent combination of smog, particle pollution and dust, exacerbated by our hot desert climate and human activity.
—Tiffany Acosta, AZCentral.com, 1 July 2025
Last year, the court upended a Biden administration effort to reduce smog and air pollution wafting across state lines.
—Cnn, Mercury News, 20 June 2025
The turbines emit nitrogen oxides, a key contributor to smog, and formaldehyde, among other pollutants, according to their manufacturer.
—Bracey Harris, NBC news, 17 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 1 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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