GRAPHIC-How air quality has improved during the coronavirus crisis

To contain the coronavirus pandemic, billions of people have been told to stay at home. In China, authorities placed almost half a billion people under lockdown, the equivalent of nearly 7% of the world's population. Many other countries have since taken similar measures, initially in hard-hit Italy and Spain, and more recently in the United States and India.

The restrictions have sent financial markets into free fall. But they have also given residents in some of the world's most polluted cities something they have not experienced in years: clean air.