In India, the coronavirus cloud has a silver lining: clear blue skies.

India entered the world's biggest lockdown last month and the government ordered 1.3 billion people to stay home as the number of coronavirus cases climbed.

The jury is still out on the effectiveness of those stringent measures in halting the spread of COVID-19. India has some 6,000 active cases and more than 200 deaths, with the number of new cases rising steadily. But the lockdown measures seem to have inadvertently solved, at least temporarily, another public health crisis: air pollution.

Across India, vehicular traffic has been cut to almost zero. Big industries billowing black smoke into the atmosphere are closed. Construction sites that are usually buzzing with activity, spewing dust and dry cement particles into the air, are eerily vacant.

All this has dramatically reduced the concentration in the air of fine particulate matter known as PM2.5 and PM10.

Perhaps nowhere is the drop in pollutants more pronounced than in the country's capital New Delhi, which usually has some of the dirtiest air in the world.

Delhi residents are used to looking up to see a hazy, gray sky. Now they're posting pictures of clear blue horizons on social media.

The air is typically so polluted that it leaves an acrid taste. During winter, smoke from crops burning across northern India wafts into the city and the pollution reading crosses 900 — up to 20 times above the safe limit prescribed by the World Health Organization. Flights are grounded periodically and schools are forced to close.

In late March, as India began its 21-day lockdown, the Air Quality Index in Delhi dropped as low as 45. Around the same time last year, it was about 160. Since the lockdown, Delhi and its suburbs have even enjoyed days when the air quality was officially classified as "good" — the best category. That's happened only a handful of times in the past few years.

India's central pollution control board says 85 Indian cities noted an improvement in air quality during the first week of the lockdown. In Jalandhar, in the northwestern state of Punjab, pollution levels dropped to their lowest in a decade and residents were able to spot snow-capped Himalayan peaks more than 100 miles away.

Social media is flooded with pictures of things that people can suddenly see from their windows — some more believable than others. One person joked he could see the Eiffel Tower from central India. Another said they spotted aliens on Mars. And someone wrote that he could see gods from his balcony.

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