The Great Smog also referred to as the Big Smoke, befell London starting on 5 December 1952, and lasted until 9 December 1952. This catastrophe caused or advanced the death of thousands and formed an important impetus to the modern environmental movement.

Early in December 1952, a cold fog descended upon London. Because of the cold, Londoners began to burn more coal than usual. The resulting air pollution was trapped by the inversion layer formed by the dense mass of cold air. Concentrations of pollutants, coal smoke in particular, built up dramatically. The problem was made worse by use of low-quality high-sulfur coal for home heating in London in order to permit export of higher-quality coal, because of the country's tenuous economic situation [1]. The "fog," or smog, was so thick that driving became difficult or impossible. It entered indoors easily, and concerts and screenings of films were cancelled as the audience could not see the stage or screen.

Since London was known for its fog, there was no great panic at the time. In the weeks that followed, the medical services compiled statistics and found that the fog had killed 4,000 people—most of whom were very young or elderly, or had pre-existing respiratory problems. There was belief that Queen Mary The Queen Dowager, then aged 85 and suffering with respiratory problems, was not at Buckingham Palace at the time of the incident. Another 8,000 died in the weeks and months that followed.

These shocking revelations led to a rethinking of air pollution; the disaster had demonstrated its lethal potential to people around the world. New regulations were put in place restricting the use of dirty fuels in industry and banning black smoke. These included the Clean Air Acts of 1956 and of 1968, and the City of London (Various Powers) Act of 1954.

Cause of mortality

Deaths in most cases during the Great Smog was due to respiratory tract infections from hypoxia (low level of oxygenation of blood) due to mechanical obstruction of the air passages by pus arising from lung infections due to smog. The lung infections were mainly bronchopneumonia or acute purulent bronchitis superimposed upon chronic bronchitis. ^[1]