smog

Smog is a form of air pollution that reduces visibility and degrades air quality. It results from the interaction of pollutants released into the atmosphere with weather conditions that trap them near the ground. The word smog is a contraction of smoke and fog and was coined in the early 20th century to describe smoky, foggy conditions in industrializing cities, later exemplified by London's Great Smog of 1952.

There are two main types of smog. Sulfurous smog, or London smog, forms when sulfur dioxide and particulate matter from burning coal react with fog in cool, damp conditions. Photochemical smog, or urban/LA-type smog, develops in sunny climates when nitrogen oxides and volatile organic compounds react under sunlight to produce ozone and other oxidants.

Common ingredients include fine particulate matter (PM2.5 and PM10), sulfur dioxide, nitrogen oxides, and ground-level ozone. Weather factors such as temperature inversions, low wind, and high humidity help concentrates these pollutants near the surface, allowing smog to persist for days or weeks.

Health effects range from eye irritation and coughing to worsening asthma, bronchitis, and cardiovascular events. Sensitive groups include children, the elderly, and people with existing respiratory or heart conditions. Smog also reduces visibility and can corrode buildings and damage crops in severe cases.

Mitigation focuses on reducing emissions from industry, transportation, and energy production. Strategies include switching to cleaner fuels, implementing emission controls, improving energy efficiency, and urban planning to reduce vehicle use. Air quality monitoring and public advisories help minimize exposure during high-smog events.