The screenshots began to circulate on Delhi WhatsApp groups last week, captioned with varying expressions of disbelief. Having checked the air quality index, something of a sadistic morning ritual among residents of India’s capital, most could not believe their eyes.

Gone was the familiar menacing red banner, indicating how each intake of breath is really just a toxic blast on the lungs, replaced instead by a healthy, cheerful green. Could it really be that Delhi’s pollution levels now fell into the category of … “good”? “It’s positively alpine!” exclaimed one message.

A nationwide lockdown imposed across India almost two weeks ago to stop the spread of the coronavirus – the largest lockdown of its kind attempted anywhere – has led to widespread chaos and suffering, especially among the country’s 300 million poor. Yet in Delhi, the world’s most polluted city, it has also resulted in some of the freshest air the capital has seen in decades.