Mumbai was the third most polluted among 10 international cities during the first three weeks of the lockdown imposed owing to the COVID-19 pandemic, according to a recent study.

Researchers studied 10 cities having relatively high coronavirus cases

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.

Mumbai ranked 3rd most polluted city during the lockdown

Even though Mumbai witnessed a 42% reduction in average PM2.5 levels recorded between March 23 and April 13, compared to average PM2.5 levels (during the same period) over the past four years, and a 34% reduction compared to the same period in 2019, the city ranked third most polluted with PM2.5 concentration at 28.8 micrograms per cubic metre (μg/m³) during the lockdown period.

Wuhan, China was the most polluted at 35.1 μg/m³ followed by Delhi, second-most polluted at 32.8 μg/m³.

New York had the lowest PM2.5 levels at 4.4 μg/m³, which had the cleanest air across 10 cities, followed by Los Angeles USA at 5.5 μg/m³, and Madrid, Spain at 6.4 μg/m³

“Although Asian cities had higher average PM levels, we observed that cities with historically higher average PM2.5 levels such as Delhi, Mumbai, Seoul, and Wuhan, experienced more drastic reductions in particulate pollution,â€_x009d_ said Kelsey Duska, air quality outreach specialist at IQAir, reported media.

“It is likely that cities in India are still observing higher PM2.5, relative to cities in Europe or the US, because people are still using energy. This energy may be sourced from dirtier sources, such as coal-based power plants. Similarly, biomass burning or fossil fuels used for domestic heating or cooking can further contribute to this effect,â€_x009d_ said Duska