: 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
California has long held special authority under the federal Clean Air Act to set stricter emissions standards than the federal government because of the state’s historic smog problems.
—
Haley Parsley
june 22,
Sacbee.com,
23 June 2026
Bonta and environmental groups said the regulations are key to helping California continue to reduce harmful smog that worsens asthma, emphysema and heart disease.
—
Paul Rogers,
Mercury News,
22 June 2026
Huxley added heatwaves are usually caused by high air pressure systems, leading to less air movement and increasing the build-up of air pollution, with methane and other pollutants reacting to create ground-level ozone – a component of smog.
—
Jamie Hailstone,
Forbes.com,
19 June 2026
Not only that, but California has very specific fuel specifications aimed at minimizing smog.
—
Matt Egan,
CNN Money,
17 June 2026
See All Example Sentences for smog
Examples are automatically compiled from online sources to
show current usage.
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Haley Parsley
june 22,
Sacbee.com,
23 June 2026
Bonta and environmental groups said the regulations are key to helping California continue to reduce harmful smog that worsens asthma, emphysema and heart disease.
—
Paul Rogers,
Mercury News,
22 June 2026
Huxley added heatwaves are usually caused by high air pressure systems, leading to less air movement and increasing the build-up of air pollution, with methane and other pollutants reacting to create ground-level ozone – a component of smog.
—
Jamie Hailstone,
Forbes.com,
19 June 2026
Not only that, but California has very specific fuel specifications aimed at minimizing smog.
—
Matt Egan,
CNN Money,
17 June 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 28 Jun. 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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