What is smog? How is classical smog different from photochemical smog?

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Smog is a type of air pollution that results from a mixture of smoke and fog. It is typically found in urban areas with high levels of industrial activity and traffic emissions. Smog can have detrimental effects on human health and the environment, leading to respiratory problems, eye irritation, and damage to plants and buildings.

There are two main types of smog: classical smog and photochemical smog.

1. Classical Smog: Also known as "London smog" or "sulfurous smog," classical smog is primarily composed of sulfur dioxide (SO2) and particulate matter. It occurs in cities where coal is burned for heating and industrial purposes. In classical smog, sulfur dioxide reacts with moisture and other compounds in the atmosphere to form sulfuric acid and sulfate particles, which combine with fog to create the characteristic haze.

2. Photochemical Smog: Unlike classical smog, which is primarily caused by sulfur dioxide emissions, photochemical smog is formed as a result of the reaction between sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs) in the atmosphere. This type of smog is commonly found in cities with high levels of automobile exhaust and industrial emissions. In photochemical smog, sunlight triggers a series of complex chemical reactions involving NOx and VOCs, leading to the formation of ground-level ozone and other secondary pollutants.

In summary, classical smog is primarily caused by sulfur dioxide emissions from burning coal, while photochemical smog results from the interaction of sunlight with nitrogen oxides and volatile organic compounds emitted by vehicles and industries. Both types of smog pose significant challenges to air quality and public health, underscoring the importance of measures to reduce emissions and mitigate the impacts of air pollution.