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A bittersweet silver lining to the COVID-19 virus is how clean the air in some of the world’s most polluted cities has become.

New Delhi is one of many megacities around the world reporting much fresher air for the first time in years since the virus forced people inside two weeks ago.

Members of a Delhi Whatsapp group exchanged screenshots of the daily air quality index last week, not believing their eyes when they saw that a green banner had replaced the familiar ominous red banner, indicating the conditions were “good.”

“It’s positively alpine,” one person wrote, according to the Guardian.

Dr. Shashi Tharoor, a Delhi politician and environmentalist, called the improved air quality a wake-up call.

“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,” Tharoor said. “Today the typical Delhi AQI hovers around 30 and one blissful afternoon, after a spurt of rain, it dropped to seven.”

Cities like Bangkok, Beijing, Sao Paulo and Bogota, which all have some type of stay-at-home order in place, are reporting unprecedented levels of clean air. The sad irony is, few can enjoy the blue skies and fresh air since most everyone has to stay inside.

The drop in pollution shows how deadly a role cars play in India’s pollution, said Delhi environmentalist Sunita Narain.

Narain stressed environmentalists aren’t “celebrating” the virus that has ravaged many cities.

“We have to make sure we take this breath of fresh air and think about the serious efforts we need to deal with pollution in Delhi.”