: 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
Mold spores and rust bloom around the bathroom fixtures, and a mysterious black smog pours from her vents and sticks to her walls.
—
Ilana Arougheti, Kansas City Star, 18 Sep. 2025
For example, Erin Brockovich-style reporting is finding that in Memphis, Tennessee, Elon Musk’s xAI supercomputer, Colossus, is worsening air quality due to its massive use of methane-gas turbines, emitting a smog of nitrogen oxides and toxic formaldehyde.
—Michaela Rychetska, JSTOR Daily, 18 Sep. 2025
In early April, the Southern Environmental Law Center estimated the turbines could produce, in a year, between 1,200 and 2,000 tons of nitrogen oxides, a smog-forming pollution associated with poor respiratory health in nearby areas, as well as the carcinogen formaldehyde.
—Taylor Kate Brown, ProPublica, 17 Sep. 2025
Indeed, orbiting Earth-observation satellites routinely use lasers for light-detection and ranging (lidar) on the planet's surface, despite the clouds and smog, while Chinese scientists have recently conducted the first ever daytime laser-ranging experiment from Earth to the moon.
—Keith Cooper, Space.com, 15 Sep. 2025
See All Example Sentences for smog
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Ilana Arougheti, Kansas City Star, 18 Sep. 2025
For example, Erin Brockovich-style reporting is finding that in Memphis, Tennessee, Elon Musk’s xAI supercomputer, Colossus, is worsening air quality due to its massive use of methane-gas turbines, emitting a smog of nitrogen oxides and toxic formaldehyde.
—Michaela Rychetska, JSTOR Daily, 18 Sep. 2025
In early April, the Southern Environmental Law Center estimated the turbines could produce, in a year, between 1,200 and 2,000 tons of nitrogen oxides, a smog-forming pollution associated with poor respiratory health in nearby areas, as well as the carcinogen formaldehyde.
—Taylor Kate Brown, ProPublica, 17 Sep. 2025
Indeed, orbiting Earth-observation satellites routinely use lasers for light-detection and ranging (lidar) on the planet's surface, despite the clouds and smog, while Chinese scientists have recently conducted the first ever daytime laser-ranging experiment from Earth to the moon.
—Keith Cooper, Space.com, 15 Sep. 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 20 Sep. 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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