Abstract
This fourβday fog caused at least 4,000 deaths and much illness; it therefore ranks as the most disastrous event of its kind known to have occurred anywhere in the world. For the first time in an incident of this kind extensive measurements were made of the daily concentrations of smoke and sulphur dioxide and of the general pattern of pollution throughout the area.
Mean concentrations of smoke and sulphur dioxide at 12 daily testβsites increased sharply on the first day of the incident and, after 3 to 4 days, averaged 1.6 mg/m^3^ and 0.7 parts per million respectively, or about 5 to 6 times normal. At individual sites in the central London area concentrations rose to 10 times normal.
There was a striking parallelism between the mean daily concentration of smoke and sulphur dioxide and the total number of deaths on those days but the latter returned the more slowly to normal.
A few data, relating to a severe London fog of 1948, indicated that the concentrations of pollution then reached about 50 to 70 per cent of the 1952 values.
The approximate distribution of sulphur dioxide is shown on a map which indicates zones of maximum pollution mainly in the riverside areas, and particularly Westminster and adjacent boroughs.