Industrial (gray) smog is primarily caused by sulfurous pollutants from coal burning and is more common in which climate?

• A. Cool, humid climates with heavy coal use.
• B. Hot, dry climates with abundant sunlight.
• C. Arid, windy climates with minimal moisture.
• D. Tropical climates with high rainfall.

Answer: (A)

Industrial gray smog forms when sulfur compounds from burning coal accumulate in cool, humid air that easily forms fog. In these conditions, sulfur dioxide is released and, in the presence of moisture, becomes sulfuric acid aerosols. These aerosols combine with the fog and soot to create a dense gray haze. Cool, humid climates with heavy coal use provide both the emissions and the atmospheric conditions (fogging and moisture) needed for gray smog to persist, making it most common there. In hot, dry, sunny climates, smog is more often the photochemical kind driven by sunlight and ozone; arid, windy areas lack the moist, fog-forming conditions; tropical regions with high rainfall tend to wash out pollutants, reducing smog formation.