(CNN) Lockdowns restricting travel and industry imposed to halt the spread of coronavirus have resulted in unprecedented reductions in deadly air pollution around the world, new analysis shows.

Major cities that suffer from the world's worst air pollution have seen reductions of deadly particulate matter by up to 60% from the previous year, during a three-week lockdowns period.

Researchers from IQAir -- a global air quality information and tech company -- studied 10 major cities around the world which have relatively high numbers of coronavirus cases and Covid-19 lockdown measures.

The study compared levels of harmful microscopic particulate matter known as PM 2.5. The pollutant, which is smaller than 2.5 micrometers in diameter, is considered particularly dangerous as it can lodge deep into the lungs and pass into other organs and the bloodstream, causing serious health risks.

Seven out of the 10 cities studied, including New Delhi, Seoul, Wuhan and Mumbai, saw significant improvements in air quality. Those with historically higher levels of PM2.5 pollution witnessed the most substantial drops in pollution.