London, June 14 (TIWN) While outdoor pollution level appeared to drop during Covid-induced periods of lockdown, particulate matter (PM) 2.5 levels were on average 23 per cent higher indoors, according to a new study of 10 global cities.

The cities included London, Paris, Berlin, Milan, New York, Toronto, Manila, Kuala Lumpur, Bangkok and Seoul.  Particle pollution was found to be high indoors in most cities even after the lockdown had lifted.