Delhi is remarkable as a air polluted city but now it’s sky see clean and fresh.

It’s air quality has improved remarkably during the shutdown

When India shut down last month and suspended all transport to contain the spread of coronavirus, the skies over its polluted cities quickly turned an azure blue, and the air, unusually fresh.

As air pollution plummeted to levels unseen in living memory, people shared pictures of spotless skies and even Himalayan peaks from cities where the view had been obscured by fog for decades.

On one social messaging group, a resident of the capital, Delhi, which regularly records some of the foulest air in the world, celebrated the city's "alpine weather". Politician and author Shashi Tharoor wrote that the "blissful sight of blue skies and the joy of breathing clean air provides just the contrast to illustrate what we are doing to ourselves the rest of the time".

Less than six months ago, Delhi was gasping for breath. Authorities said air quality had reached "unbearable levels". Schools were shut, flights were diverted, and people were asked to wear masks, avoid polluted areas and keep doors and windows closed.

Delhi and 13 other Indian cities feature on a list of the world's 20 most polluted. It is estimated that more than a million Indians die every year because of air pollution-related diseases. Industrial smoke, vehicular emissions, burning of trash and crop residue, and construction and road dust are the major contributors.

As urban Indians gazed at the skies and breathed clean air inside their homes, researchers hunkered down to track data on how the grinding lockdown - now extended to 3 May - was impacting air pollution across the country.