Photochemical smog was first identified in Los Angeles in 1944. Although several other kinds of smog occur, photochemical smog (or Los Angeles-type smog) is a yellow-brown haze produced by the reaction of sunlight with exhaust from automobiles and power plants that burn coal. Ozone, nitrogen dioxide, and other volatile organic compounds that make up this smog irritate eyes and nasal passages. These are particularly dangerous to people who have heart disease, asthma, or other respiratory illnesses, and to anyone who exercises or does manual labor outdoors when smog is heavy.
Photochemistry of Los Angeles-Type Smog
As its name implies, photochemical smog forms in the presence of light, so this type of smog is seen most frequently during the hot and sunny summer months. Though the components of photochemical smog might be in the air, if sunlight does not reach them or they are not concentrated enough, the smog will not form. The worst cases of smog occur when winds are calm and smog is trapped near the surface by a temperature inversion, a condition in which cooler air near Earth's surface has warmer air above it. These ideal smog-forming conditions commonly occur near cities that are adjacent to mountains.
Photochemical smog forms through a series of chemical reactions among compounds in the atmosphere. When nitric oxide (NO), a component of the exhaust from cars and power plants, enters the atmosphere, it reacts with oxygen to produce nitrogen dioxide (NO2). Sunlight can break nitrogen dioxide down. This process initiates other chemical reactions that lead to the formation of low-level ozone. Although ozone (O3) that is high in the stratosphere filters out harmful UV radiation, ozone's presence at the ground level poses a health risk. Also, Volatile Organic Compounds (VOCs), molecules that enter the atmosphere from substances such as gasoline, cleaning solvents, and trees, play a crucial role in forming photochemical smog.
Photochemical smog was first identified in Los Angeles in 1944. Although several other kinds of smog occur, photochemical smog (or Los Angeles-type smog) is a yellow-brown haze produced by the reaction of sunlight with exhaust from automobiles and power plants that burn coal. Ozone, nitrogen dioxide, and other volatile organic compounds that make up this smog irritate eyes and nasal passages. These are particularly dangerous to people who have heart disease, asthma, or other respiratory illnesses, and to anyone who exercises or does manual labor outdoors when smog is heavy.
Photochemistry of Los Angeles-Type Smog
As its name implies, photochemical smog forms in the presence of light, so this type of smog is seen most frequently during the hot and sunny summer months. Though the components of photochemical smog might be in the air, if sunlight does not reach them or they are not concentrated enough, the smog will not form. The worst cases of smog occur when winds are calm and smog is trapped near the surface by a temperature inversion, a condition in which cooler air near Earth's surface has warmer air above it. These ideal smog-forming conditions commonly occur near cities that are adjacent to mountains.
Photochemical smog forms through a series of chemical reactions among compounds in the atmosphere. When nitric oxide (NO), a component of the exhaust from cars and power plants, enters the atmosphere, it reacts with oxygen to produce nitrogen dioxide (NO2). Sunlight can break nitrogen dioxide down. This process initiates other chemical reactions that lead to the formation of low-level ozone. Although ozone (O3) that is high in the stratosphere filters out harmful UV radiation, ozone's presence at the ground level poses a health risk. Also, Volatile Organic Compounds (VOCs), molecules that enter the atmosphere from substances such as gasoline, cleaning solvents, and trees, play a crucial role in forming photochemical smog.
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