London's Great Smog of December 1952 was caused by the carbon monoxide, sulfur oxides, and soot released by the burning of large amounts of coal within the city. A series of several windless days allowed the pollutants to accumulate and with the fog droplets to form a toxic smog with a pH of just 1.6, a level that made it almost as corrosive as sulfuric acid.
例如 1952 年 12 月在英國倫敦發生的「煙霧事件」，就是因為當時市區大量燃煤所排放的一氧化碳、硫氧化物、粉塵等污染物質，在連續數日平靜無風的天氣條件下大量蓄積，再與霧滴結合形成 pH 值僅 1.6 的「酸毒霧」，幾乎和硫酸一樣具有高度腐蝕性。