Photographs of smog enveloping Beijing’s Bird’s Nest stadium became one of the defining images of the first decade of this century. China’s annual air pollution deaths reached 2.6 million people a year in 2005. At the time, Beijing was crowned smog capital of the world and concerns for the health of athletes overshadowed preparations for the 2008 Olympic Games.
But rapid improvements followed, with clean-up technologies fitted to coal-burning power stations and industrial plants, followed by their conversion to fossil gas. New vehicles were fitted with tighter emissions controls and fuels were improved.
However, while figures from the city government show that particle pollution in Beijing reduced by more than 60% over the 10 years from 2013 to the end of 2022, it is still six times greater than the World Health Organization guidelines.
But a new study gives more insight to the origins of some of that pollution. In 2018, Dr Kaspar Rudolf Dällenbach and an international team set up one of the world’s most sophisticated air pollution measurement sites on the roof of the Beijing University of Chemical Technology.
Dällenbach, from Switzerland’s Paul Scherrer Institut, said: “Despite continuous air quality improvements over the last decade, Beijing is still affected by air pollution episodes. I wanted to know why.”
The scale and complexity of the challenge to reduce Beijing’s air pollution was further revealed during Covid lockdowns. Dällenbach explained: “With substantial decreases in traffic, coal consumption and overall economic activity, one might have expected a significant drop in pollution levels. However, we found that particle pollution remained high.”
The team’s research – thanks to its ability to analyse air pollution at a molecular level and track changes in carbon-containing particles in near-real-time – revealed that Beijing’s air pollution often starts outside the city.
Dällenbach said: “Before smog in Beijing forms, pollutants are transported over hundreds of kilometres, making this a regional issue. To solve it, coordinated and stringent large-scale measures are needed across one of the most populated regions on the planet.”
In winter, the team found particle pollution from solid fuel burning for heating – wood and coal – with the most severe air pollution periods being dominated by sources in the greater Beijing–Tianjin–Hebei area and the mountains to the west. In summer, air flows in from the south and pollution is dominated by urban emissions – including solvents and petrochemicals from traffic and industry, probably from the Xi’an-Shanghai-Beijing belt and taking in pollution from far as 600 miles away.
Dällenbach said there were lessons for other cities, including those in Europe. “Air pollution doesn’t stop at country borders,” he said. “Mitigation strategies are needed that operate both on the European scale and the local scale.”
