smog

American  

[smog, smawg] / smɒg, smɔg /

noun

1. smoke or other atmospheric pollutants combined with fog in an unhealthy or irritating mixture.

2. photochemical smog.

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verb (used with object)

1. to cover or envelop with or as if with smog.

smog British  

/ smɒɡ /

noun

1. a mixture of smoke, fog, and chemical fumes

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smog Scientific  

/ smŏg /

1. A form of air pollution produced by the reaction of sunlight with hydrocarbons, nitrogen compounds, and other gases primarily released in automobile exhaust. Smog is common in large urban areas, especially during hot, sunny weather, where it appears as a brownish haze that can irritate the eyes and lungs. Ozone, a toxic gas that is not normally produced at lower atmospheric levels, is one of the primary pollutants created in this kind of smog.

2. Also called photochemical smog

3. Fog that has become polluted with smoke and particulates, especially from burning coal.

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smog Cultural  

1. A haze or fog composed of water vapor, complex molecules, and suspended particles.

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Discover More

In North America, the primary cause of smog is pollution from automobile exhaust.

The Los Angeles basin, where pollutants can be trapped by inversions and the surrounding mountains, has frequent problems with smog, as do other major urban areas.

The word smog is a combination of smoke and fog.

Other Word Forms

• desmog
  verb (used with object)
• smoggy
  adjective
• smogless
  adjective

Etymology

Origin of smog

1900–05; sm(oke) + ( f)og ¹

Explanation

What do you get when you combine "smoke" and "fog"? Smog! Smog is the thick haze or smoke that's caused by polluting substances in the air. Generally, the more cars there are in a city, the more likely there is to be smog. There are other culprits for smog, though, including coal-burning factories, other chemical emissions from plants and mills, and nearby forest fires. If there's too much smog in a city, it can make it hard for people with asthma to breathe.Smog is a great example of a portmanteau, a word formed by combining two other words into one: it comes from smoke and fog.

Example Sentences

See Examples For:

smog

Michigan Rep. John James, running for governor in a state that saw some of the worst air pollution from the smog, announced he would introduce legislation imposing sanctions on Canada.

From Slate ● Jul. 21, 2026

Wildfires burning in Canada have sent the noxious smog billowing across the border, with residents in New York, Washington and the US Midwest urged to stay indoors due to dangerously low air quality.

From Barron's ● Jul. 18, 2026

Roughly a quarter of U.S. gasoline is a cleaner-burning blend of petroleum-derived chemicals called “reformulated gasoline,” which is required in urban areas across 17 states and the District of Columbia to reduce smog.

From Salon ● May 13, 2026

One problem is that ethanol blends greater than 10% can increase smog during warm weather, which is why the EPA restricts its sale during the summer.

From The Wall Street Journal ● May 10, 2026

A smog is technically a mixture of smoke, fog and chemical fumes but this was a mixture of smoke, smoke and more smoke.

From "The London Eye Mystery" by Siobhan Dowd

Related Words

• acid rain
• carbon dioxide
• fog
• smoke
• soot