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photochemical smog
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Thick brown layer of smog obscures the Los Angeles skyline, with city buildings and neighborhoods visible beneath a blue sky.
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photochemical smog

air pollution
Also known as: Los Angeles smog
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Thick brown layer of smog obscures the Los Angeles skyline, with city buildings and neighborhoods visible beneath a blue sky.
Los Angeles smog A pall of photochemical smog over Los Angeles in November 2016. Photochemical smog, which is also known as “Los Angeles smog,” occurs most prominently in urban areas that have large numbers of automobiles, and it requires neither smoke nor fog.

Photochemical smog is a type of air pollution that occurs in urban areas with significant automobile traffic. It is characterized by a brownish haze caused by the action of sunlight on pollutants like nitrogen oxides and hydrocarbon vapors, primarily from vehicle exhaust.12

This process creates ozone, a toxic gas that irritates the eyes and respiratory system, and can damage plants. Unlike sulfurous smog, which results from burning fossil fuels like coal, photochemical smog does not require smoke or fog. High concentrations of ozone are considered unhealthy and are common in cities with heavy traffic and ample sunshine, especially when weather patterns trap pollutants.13

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  2. air pollution - Ozone
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