Despite its history of air pollution dating back centuries, Londoners seemed slow to learn from their mistakes. Air pollution from coal burning continued into the 1960s. The sulfur dioxide combined with London’s famous fog, with the result being acid fog. In 1952, the thick fog became so dense that people could not see to walk or drive. Influenza, bronchitis, and pneumonia cases skyrocketed, and about 4,000 people died and another 100,000 were sickened that year from illnesses related to this killer fog.