In December 1952, London experienced one of the worst air-pollution episodes in its history when a persistent anticyclone and cold weather trapped smoke and sulfurous pollutants over the city. Beginning on December 5 and lasting until December 9, the event—commonly called the Great Smog—reduced visibility to a few metres in many areas, disrupted transportation, closed schools and businesses, and caused widespread respiratory distress. Contemporary estimates and later epidemiological studies concluded that the smog was associated with a sharp, temporary rise in mortality and morbidity, mainly among the elderly, infants, and people with preexisting respiratory or cardiovascular conditions. Conditions and causes The episode followed several days of cold weather when Londoners burned large quantities of low-quality, sulfur-rich coal for domestic heating and in power stations. A temperature inversion and very little wind prevented the normal dispersion of smoke and industrial emissions. The mixture of sulfur dioxide, smoke particulates (soot), and other combustion products combined with fog to form a dense, acidic smog. The visibility-reducing fog invaded offices, cinemas, theatres, hospitals and the underground, and reached concentrations that interfered with everyday activity and posed acute health risks. Human impact and response Hospitals reported increased admissions for bronchitis, pneumonia and other respiratory problems. Ambulance services and funeral directors were overtaxed. Contemporary reports and later research disagree on precise death tolls: an initial official estimate attributed roughly 4,000 excess deaths to the episode in the weeks that followed, while subsequent statistical analyses suggest the excess mortality may have been higher—often cited around 12,000 excess deaths when accounting for a longer window of related health effects. Thousands more suffered nonfatal illnesses and long-term health consequences. The public reaction was swift and angry. Press coverage and medical testimony highlighted the links between coal smoke, industrial emissions and the crisis. The scale and visibility of the disaster helped galvanize political will for reform. Policy aftermath The Great Smog led directly to major legislative and regulatory changes in the United Kingdom. The most notable was the Clean Air Act of 1956, which introduced smokeless zones in urban areas, restricted the types of fuel that could be burned, and encouraged cleaner domestic and industrial heating. The episode also accelerated efforts to relocate polluting industries away from dense urban centres and to modernize household heating. Over subsequent decades these measures, alongside changes in fuel use and technology, contributed to substantial reductions in urban smoke and sulfur pollution in Britain. Historiography and legacy Scholars treating the 1952 smog note both its immediate human toll and its role as a turning point in public health and environmental policy. While numbers for deaths and illnesses vary by study and methodology, the consensus is that the smog was a severe public-health disaster that exposed the lethal risks of uncontrolled urban air pollution. The incident remains an important case study in environmental history, urban planning, and public-health policy, cited as a catalyst for modern air-quality regulation in the UK and elsewhere. Caveats Details such as the precise number of excess deaths attributed to the smog depend on the study period and statistical methods used; estimates in scholarship differ and are typically presented as ranges. This summary relies on the established historical record of the 1952 London smog and subsequent public-health and legislative responses.