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Great Smog 70 years on: ‘New laws to clean London’s air’

One of the UK’s worst air pollution episodes, the Great Smog of 1952, occurred 70 years ago in London. Pollution laws, and changes in the way we heat and power, have prevented dangerous smogs from reoccurring. New air pollution reduction targets have been set, but a return to burning solid fuels may jeopardise this winter’s air quality.

What caused the Great Smog of London in 1952?

From 5-9 December 1952, the capital city was blanketed in a toxic smog created by cold weather – a combination of increased coal burning to heat homes and a temperature inversion.

During a temperature inversion, instead of cooling as it typically does, the temperature of the air increases with height above the ground. With colder heavier air trapped beneath warm air above, pockets of stagnated and ever more polluted air can form close to the Earth’s surface until a change in the weather creates mixing.

“In early December 1952, a very cold and anticyclonic weather system led to an inversion, trapping pollutants from both homes and industries. Coal-burning led to large emissions of soot particles, sulfur dioxide gas, and hydrochloric acid. Further chemical reactions in the air led to high levels of smoke-laden fog, known as smog.” explains Professor Jacqui Hamilton, Science Director at the National Centre for Atmospheric Science and air quality researcher at the University of York.

Impacts of clean air legislation

Following the Great Smog of 1952, a series of laws were rapidly introduced – the first of their kind in the world. The Clean Air Acts of 1956 and 1968 banned black smoke emissions, and pushed for – and incentivised –  residents and factory operators to convert to using smokeless fuels, and later to North Sea gas. 

While it took some years to take full effect, black smoke and sulfur dioxide concentrations dropped dramatically following the introduction of the legislation. 

Pollution laws and changes in the way we heat our buildings, and power industry, have meant toxic and recurrent smogs that are heavy in black soot and sulfur are uncommon now.

Widespread use of gas and electric central heating, and other controls on emissions in industry, have significantly improved the quality of the air we breathe.

New laws for UK air quality

While at a national level air pollution emissions continue to reduce, poor air quality still continues to be the greatest environmental risk to human health and nature.

In 2020 the UK’s government stated an ambition to be the ‘first generation to leave the environment in a better state than in which we found it’ and to deliver a green exit from the European Union. It introduced the Environment Act in 2021 – the first environmental protection bill for 20 years.

The government is now required to set binding targets on key environmental indicators, such as biodiversity protection, waste reduction, and air and water quality improvements.

For air pollution, two targets will be set. An annual target will be established for reducing the maximum allowable particulate matter concentration, and another for reducing exposure of the population to particulate matter pollution over time.

There are many sources of small particulate matter, from vehicle exhausts and tyres, to wood stoves, cooking and farming practices.

Particulate matter can bypass filters in our respiratory system and enter our bloodstream. Over the long-term, breathing in small particulate matter increases mortality rate, often by exacerbating heart and lung conditions. Long term exposure to pollution raises the risk of multiple cancers and is implicated in dementia.

Those most vulnerable to air pollution include elderly people, children and people with respiratory illnesses.

Researchers from the National Centre for Atmospheric Science are members of the Air Quality Expert Group (AQEG), who advise the government on matters relating to air pollution.

Professor Ally Lewis, Deputy Director of the National Centre for Atmospheric Science and atmospheric chemist at the University of York describes the role of AQEG: “AQEG have informed the government’s new particulate matter reduction targets by evaluating future projections of emissions and their likely feasibility, the reliability of atmospheric models for making policy forecasts, and the effectiveness of monitoring techniques as a means to test whether new legal standards have been met.”

The Environment Act 2021 took nearly two years to pass through parliament and along the way AQEG provided science advice to ministers, MPs, members of the House of Lords and government officials.

Dr Sarah Moller, a senior research fellow at the National Centre for Atmospheric Science and University of York, has led a project to map the factors, breadth and complexity of particulate matter concentrations for the Department for Environment, Food and Rural Affairs.

The particulate matter systems map demonstrates how the economy, urban planning, and population distribution affect particulate matter concentrations, and therefore the success of meeting any reduction targets.

The mapping work also informed computer modelling scenarios that calculated suitable concentration limits. These scenarios have been particularly useful, for analysing how changes in key sectors such as energy, transport, or farming will impact the proposed targets.

Dr Sarah Moller, senior research fellow at the National Centre for Atmospheric Science and University of York

Solid-fuel sources of air pollution in winter 2022

This year, soaring energy prices are now pushing people to make decisions about how and when to heat their homes. Burning solid fuels – like wood and coal – during the colder months can be perceived to be a cost-cutting choice compared to using gas or electric boilers.

Changes in air quality created by solid fuel burning, particularly increased emissions of particulate matter, can have adverse impacts on our health and the environment.

Solid fuel burners – such as log-burners – are the single biggest source of direct emissions of small particulate matter nationwide.

Across a UK measurement network, National Centre for Atmospheric Science researchers are looking out for key environmental indicators that solid fuel burning is on the rise this winter by tracking unique chemical signatures in the air.

Alongside this, the National Centre for Atmospheric Science are studying other sources of poor air quality, and their impact on human health, through involvement in the UK’s Clean Air Program.

This research will help to inform the AQEG mapping and modelling work, which will in turn provide the government with information on how socio-economic factors affect particulate matter concentrations across the country.