The 1948 Donora Smog Disaster occurred when pollutants were trapped by a temperature inversion, causing deaths and respiratory problems.

• A. Industrial Revolution
• B. Amoco Cadiz
• C. Gulf of Mexico Dead Zone
• D. Donora Smog Disaster

Answer: (D)

This item tests how atmospheric inversions can trap pollutants and create severe air pollution events. In a temperature inversion, a layer of warm air sits above cooler air near the ground, which prevents vertical mixing. Emissions from industry then accumulate at ground level, forming dangerous smog.

The Donora Smog Disaster in 1948 is the classic example: several days of heavy smog hung over Donora, Pennsylvania, because weather conditions kept pollutants from dispersing. Emissions from factories and a nearby zinc works combined with the inversion, leading to very high levels of particulate matter and sulfur dioxide, causing thousands to suffer respiratory problems and about 20 deaths. This event helped highlight the health risks of air pollution and spurred later air quality regulation and research.

The other topics aren’t about a smog event caused by trapped pollutants: one refers to a broad historical period, another to an oil spill, and another to nutrient-driven hypoxia in marine environments.