London Fog: Pollution Haze, Not Warmth

False. "London fog" (pea souper) was not caused by warm cities. It was a toxic smog resulting from:

Mechanism

• Fuel: Massive domestic/industrial burning of bituminous coal (high sulfur).
• Meteorology: Temperature inversion (cold air trapped under warm layer) + light wind + high humidity (Thames Valley).
• Chemistry: Smoke particles (soot) + sulfur dioxide (SO₂) + water vapor → sulfuric acid aerosol + carbon particles = yellow-brown-black fog.

Peak & End

• Great Smog of 1952: 4,000–12,000 excess deaths in 5 days.
• Clean Air Act 1956: Smokeless zones, tall chimneys, gas/electric shift.
• Classic "London fog" largely eliminated by 1970s.

Modern "Fog"

Today's London fog is mostly radiation fog (clear nights, moist air) – white/grey, not brown. Air quality still exceeds WHO limits for NO₂/PM2.5 (traffic), but not the historic coal smog.

Key: Color came from pollutants, not temperature. Warmth actually inhibits radiation fog formation.