: 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
Hotter areas also create more ozone smog.
—
Meg Tanaka, Los Angeles Times, 16 Feb. 2026
There was a time when smog routinely blanketed the San Fernando Valley; today, on a sunny day, the air is clear.
—Suzette Valladares, Oc Register, 15 Feb. 2026
Last year, residents in the majority-Black community of Boxtown in South Memphis testified at public hearings about a stench in the air, and the impact of worsening smog on their health caused by xAI's use of natural gas turbines.
—Lora Kolodny, CNBC, 13 Feb. 2026
The initiative is expected to significantly reduce air pollution, including smog-forming nitrogen oxides and particulate matter — tiny particles that can penetrate deep into the lungs.
—City News Service, Daily News, 10 Feb. 2026
See All Example Sentences for smog
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Meg Tanaka, Los Angeles Times, 16 Feb. 2026
There was a time when smog routinely blanketed the San Fernando Valley; today, on a sunny day, the air is clear.
—Suzette Valladares, Oc Register, 15 Feb. 2026
Last year, residents in the majority-Black community of Boxtown in South Memphis testified at public hearings about a stench in the air, and the impact of worsening smog on their health caused by xAI's use of natural gas turbines.
—Lora Kolodny, CNBC, 13 Feb. 2026
The initiative is expected to significantly reduce air pollution, including smog-forming nitrogen oxides and particulate matter — tiny particles that can penetrate deep into the lungs.
—City News Service, Daily News, 10 Feb. 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 Mar. 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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