Freezing pollution before it enters offices and homes through air conditioning units can prevent 99 per cent of fumes coming inside, scientists have discovered.

Nottingham Trent University and the Chinese Academy of Sciences have been trying to find a way to prevent deadly outdoor air pollution from seeping indoors.

They found that if pollution is frozen to around -18C in a condensing tube the particles clump together and fall to the bottom, allowing fresh clean air to pass through.

Their method was able to remove 99 per cent of particulates and 98 per cent of nitrogen oxide pollutants. It is hoped that the work could pave the way for simple modification of air conditioning and humidifier units so that they can also clean polluted indoor air.

“Hazardous outdoor air pollution has severely affected indoor air quality, threatening the health of billions of people,” said Professor Robert Mortimer, a researcher on the study and Dean of the School of Animal, Rural and Environmental Sciences at Nottingham Trent University.