Fifty years later: clearing the air over the London smog. (NIEHS News).

Between 5 December and 9 December 1952, one of the deadliest recorded episodes of urban smog occurred in London, England. New research indicates that as many as 12,000 people may have died as a result of the smog, and morality from respiratory illnesses such as bronchitis and pneumonia increased more than seven-fold during the smog. Overall death rates during the first half of that month were three times higher than normal, and morbidity and mortality rates in greater London remained elevated well into March of 1953.

The severity of the 1952 London Smog, along with the publicity surrounding it and other smog episodes in the early twentieth century, had two effects. First, they sparked an increased public health effort to understand the effects of air pollution on human health. Second, they prompted the formulation of governmental regulations on air pollution in many countries. This milestone event in the history of environmental health will be commemorated at the conference "The Big Smoke: Fifty Years after the 1952 London Smog," cosponsored by the NIEHS along with the Health Effects Institute, the Wellcome Trust, the Greater London Authority, the London borough of Camden, Sypol (a British environmental health and safety consulting group), the Shell Foundation, and the International Society for Environmental Epidemiology. Organized by Tony Fletcher and Virginia Berridge, professors of environmental epidemiology and history, respectively, at the London School of Hygiene and Tropical Medicine, the conference will be held 9-10 December 2002 at the University of London.

Programs will include historical perspectives of the 1952 London Smog and of air pollution in London in general. London had experienced smog events since the twelfth century, when coal was discovered along England's northeast coast and became the fuel of choice. But such events increased during and after the Industrial Revolution as both manufacturing and the population--both then dependent on burning large amounts of coal--expanded dramatically in the city.

For much of November 1952, temperatures in southern England were unusually low, causing people to heavily stoke their coal-burning home furnaces to keep warm. In the first days of December, high atmospheric pressure over the area caused an inversion that trapped soot and other air pollutants near ground level. Because of the smog, visibility in some areas of central London was reduced to nearly zero for 48 hours. Measurements taken at the time revealed that during that first week of December 370 metric tons of sulfur dioxide were released into the air, where it was converted into sulfuric acid. Large amounts of particulate matter also were released.

One seminar at the conference will bring together physicians, researchers, and others who remember the 1952 smog to present their eyewitness accounts of the event. These accounts will eventually be compiled into a book by historians at the London School of Hygiene and Tropical Medicine.

Other presentations will discuss the health impacts of the 1952 smog and the public health response. A presentation by Devra Davis, a visiting professor of public policy at Carnegie Mellon University, will offer a reanalysis of how public health officials handled the event at the time and new evidence indicating that as many as 12,000 deaths may have resulted from the smog. As she wrote in her recently released book When Smoke Ran Like Water: Tales of Environmental Deception and the Battle against Pollution, "The true toll of London's smog was hidden for years within official documents.... In the 1950s in London and elsewhere, public health statistics were only just starting to be retrievable for use in research."

Even though levels of sulfur dioxide and smoke in London have greatly decreased over the past 50 years, particulate matter remains a significant pollutant, and high levels of other air pollutants such as nitrogen dioxide are being detected, with London residents again experiencing significant winter pollution episodes during 1991, 1994, and 1997. David Hutchinson, an adviser with the Greater London Authority (which oversees economic development and public transportation), will present the current governmental strategy for improving air quality in the city. The plan includes a number of large-scale public transportation and energy initiatives. Proposals include increasing the number of privately owned alternative-fuel vehicles and creating low-emission zones in the city that would bar the most-polluting vehicles from those areas.

Another session will focus on the health effects of urban air pollution worldwide and air pollution episodes caused by vegetation fires. One growing urban center, Dublin, Ireland, has learned a great deal about managing air pollution. A study cofunded by the NIEHS, conducted by researchers at the Harvard School of Public Health, and published in the 19 October 2002 issue of The Lancet, found that a 1990 ban on coal sales and coal burning in Dublin has resulted in a 70% decrease in concentrations of black smoke (fine suspended particulate matter), a 15.5% reduction in deaths from respiratory causes, and a 10.3% reduction in deaths from cardiovascular causes. Michael Brauer, a professor in the School of Occupational and Environmental Hygiene at the University of British Columbia in Vancouver, believes the spread of urban areas into formerly forested or agricultural regions is a key factor in the rising incidence of air pollution episodes and human health effects from vegetation fires worldwide.

Although 50 years have passed since the Great London Smog, many people alive at the time vividly remember the smog-choked streets and shrieking ambulance sirens from those days. But thanks to the public outcry following the 1952 smog, they have also witnessed a significant improvement in air quality, public health policy, and government regulation in many countries that has greatly reduced the threat of future smog episodes.