Today in History – December 4th, 1952 – Killer fog begins in London England and the word “smog” is coined. A dense fog mixed with sooty black coal smoke killed over 12,000 Londoners in four days, remaining one of the deadliest environmental tragedies in recent history. As many of the initial deaths were elderly or ill people, the medical staff who treated patients at the time did not realize the cause and extent of the impact. It was the shortage of coffins and high sales of flowers were the first indications that many people were being killed. The effect of carbon emissions on the the environment remains today and is the major contributor to global warming.

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The Great Smog of London in 1952 is today regarded as one of the most significant pollution events in World history, leading as it did to new levels of understanding of the impact burning fossil fuels can have on the environment and the link between air quality and human health. However, rather than the threat of smog on human health diminishing due to pollution control measures, continued industrialisation has led to a new type of smog that is predicted to occur more frequently with global warming. In addition, scientists now realise that the very soot in such smog itself makes a significant contribution to global warming, a disastrous double-edged sword.

During the period of Friday 5th to Tuesday 9th December 1952 a thick, dense mixture of smoke and fog settled over London, for which the term “smog” was coined. Today this event is seen as one of the most significant pollution episodes in history, since it led directly to new ways of thinking about man’s impact on the environment and raised public awareness of the relationship between air quality and health. The huge number of deaths (initially reported as 4000, nowadays considered to be closer to 12,000) and other casualties (an estimated 100,000 people were affected by respiratory illnesses) directly attributed to the smog demonstrated its lethal potential and gave impetus to the modern environmental movement and the rethinking of air pollution and the need to control it.

In the years following the Great Smog, new laws were implemented in the UK, the Clean Air Acts of 1956 and 1968, and the City of London (Various Powers) Act 1954, to greatly restrict air pollution and improve air quality. This led to the closures of the coal-fired power stations at Battersea and other places within London and the moving of power plants to central locations in England away from the cities. These acts, and others like them across the developed world, have helped to improve air quality, but now a modern variation of the London Smog, known as photochemical smog, blights our cities, and, whereas the Great Smog was stationary and sat for several days over a windless London, this new fog travels with the wind and, hence, can affect populations well away from the cities themselves.

The London Smog was made up of black soot and tar particles and sulfur dioxide emitted mainly by the coal-fired power stations dotted around and within London. Mixed with the smoke from domestic chimneys, vehicle exhausts (particularly those from the diesel engines of the London Buses that had just replaced the more environmentally friendly trams!) and combining with the fog caused by an anticyclone settling over London, a thick “pea soup” smog (the presence of the tarry particles of soot gave the smog its yellow-back colour which led to its nickname of “peasouper”) developed and settled close to the ground, remaining motionless for several days and leading to severe breathing difficulties for those living and working within it.

In contrast, with coal-fired power stations largely removed from our cities and, in any case, in most countries now fitted with air pollution control measures to remove particulates and sulfurous oxides, the modern day version of smog is formed due to the chemical reaction of nitrogen oxides (formed in vehicle exhausts) and volatile organic compounds (VOCs, emitted from, for instance, gasoline, solvents, paints), catalysed by sunlight. This results in airborne particles that are highly reactive and oxidising and in ground-level ozone. Exposure to these pollutants can either cause or exacerbate acute respiratory diseases, decreased lung function in children, asthma and other serious health problems. It is this phenomenon that we can often see as a dirty brown stain hanging over our cities on sunny, warm and dry days. For those cities still dependent on local coal-fired power stations, such as Beijing, and combined with the soot emitted from diesel engines, the problem is even more acute. Modern-day versions of the first Clean Air Acts have significantly reduced soot emissions from coal-fired power stations and vehicle exhausts in the United States and Europe.

Scientists now believe that global warming will only add to the problem of air pollution in our cities. Higher temperatures over the coming decades are expected to cause more smoggy days and heat waves, resulting in a greater number of illnesses and deaths. However, the interactions between smog and global warming are extremely complex and are not fully understood. For instance, it is now known that aerosols, which are gaseous suspensions of very fine particles, including soot, are known to increase global warming, whereas sulfates have a cooling effect. What happens when you remove one or the other or both from emissions to the atmosphere is not known for certain. Recent studies estimate that soot in the atmosphere is responsible for 18 per cent of the planet’s global warming, compared with 40 per cent for carbon dioxide. Hence, it is believed that measures to control the emissions of soot from, for example, wood-burning stoves, could be a relatively cheap and quick way of significantly reducing global warming. Unlike carbon dioxide, soot does not linger for long in the atmosphere, but travels immense distances to deposit on snow-capped mountains and polar ice caps, significantly reducing the ability of the snow and ice to reflect the sun’s energy. It is from Asia and Africa where most of the soot emanates.

There are over 700 million wood-burning stoves in use in the World today. Several initiatives are underway to encourage communities in India and Africa to use new stoves that do not emit soot. One such project has come up with an innovative stove for use in the war-torn region of Darfur. Known as the Darfur Stoves project and led by scientists from the Lawrence Berkeley National Laboratory (http://darfurstoves.org/), the new stove requires only one quarter of the amount of firewood needed to cook using the traditional three-stone fires. Because of its fuel efficiency, use of the new stove limits the amount of time the women in Darfur need to spend outside the safety of the displaced persons camps to gather fuel for cooking. This decreases their exposure to possible violent attacks, whilst also limiting deforestation and the release of toxic indoor smoke. However, in common with a similar initiative in Kohlua, India (http://www.nytimes.com/2009/04/16/science/earth/16degrees.html) there is a reluctance from the communities involved to use these new stoves, partly because the food prepared on them tastes very different to what they are used to (and happy with) and partly because of cultural and traditional values. This is a lesson that must be learnt. If we are to encourage people to change their behaviours to combat global warming, we must work with them to develop technologies appropriate to their needs.

I am Director of the the Centre for CO₂ Technology at University College London, established in response to the Kyoto Protocol and the recognition that existing technologies will not be able to meet the emission targets agreed upon for carbon dioxide (as the main greenhouse gas). Thus, the Centre focuses on developing breakthrough technologies for the large scale reduction (e.g. alternative, low carbon, energy sources), removal (e.g. gas separation from flue emissions) and sequestration (e.g. long term storage in materials) of carbon dioxide.

My personal research interests lie in the development of technologies that radically change the ways that chemicals are made today, so that the energy demand from the chemicals sector is massively reduced. I am also interested in looking into ways to involve all stakeholders in the development of low carbon technologies, in order to encourage deployment of said technologies, a process known as Open Innovation. See http://www.ucl.ac.uk/climate-change/ for the work UCL is doing on climate change. My piece is available at the link “The Next Industrial Revolution”.

For more information, see the EEngineering Pathway’s educational resources on global warming and smog and air pollution. For related curricula, visit the Chemical Engineering Education or Environmental Engineering Education disciplinary communities.

Also on this date in 1996, NASA’s Mars Pathfinder and Sojourner rover launched from Cape Canaveral.