: 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 vehicle emissions standards than the federal government because of the state’s historic smog problems.
—
Madison Smalstig, Sacbee.com, 13 Mar. 2026
Opponents argue that xAI understated the amount of pollution that will be emitted by its turbines in its permit application, with particular concerns around smog-forming nitrogen oxides and other pollutants that can be harmful to human health, including formaldehyde and airborne particulate matter.
—Lora Kolodny, CNBC, 10 Mar. 2026
Crude droplets rained over Tehran after Israeli airstrikes decimated oil depots, draping the Iranian capital in a dense smog.
—Gavin J. Quinton
march 10, Los Angeles Times, 10 Mar. 2026
Starting in January and February, refiners start transitioning to the state’s unique summer blend of fuel that helps reduce smog but is more expensive than the winter formula.
—Rob Nikolewski, San Diego Union-Tribune, 3 Mar. 2026
See All Example Sentences for smog
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Madison Smalstig, Sacbee.com, 13 Mar. 2026
Opponents argue that xAI understated the amount of pollution that will be emitted by its turbines in its permit application, with particular concerns around smog-forming nitrogen oxides and other pollutants that can be harmful to human health, including formaldehyde and airborne particulate matter.
—Lora Kolodny, CNBC, 10 Mar. 2026
Crude droplets rained over Tehran after Israeli airstrikes decimated oil depots, draping the Iranian capital in a dense smog.
—Gavin J. Quinton
march 10, Los Angeles Times, 10 Mar. 2026
Starting in January and February, refiners start transitioning to the state’s unique summer blend of fuel that helps reduce smog but is more expensive than the winter formula.
—Rob Nikolewski, San Diego Union-Tribune, 3 Mar. 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 17 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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