Coral Davenport

In India, where some of the most polluted skies in the world turned clear and blue for the first time in decades, Sarath Guttikunda, director of Urban Emissions.info, a New Delhi-based research organization, spent the shutdown monitoring air quality data gathered by government-operated atmospheric monitors across 122 Indian cities. “This is a really good experiment that we hope will never be repeated again,” he said. “Every day we learned something new.”

In a country where much of the population suffers under an opaque stew of pollution, the Indian government has little information about which sources of emissions — cars, power plants, factories or cookstoves — are the worst culprits, Dr. Guttikunda said. But as the shutdown cleared cars off the roads and brought factories to a halt, coal plants and cookstoves kept emitting. That allowed Dr. Guttikunda and his colleagues to develop a more precise profile of pollution, source by source, city by city, region by region.

“If you want to clean up your air pollution problem, you have to know what to target,” he said.

Other experts agreed. “These studies, particularly in India, can make it much easier to get a good bead on emissions,” said Maureen Cropper, a senior fellow at Resources for the Future, a nonpartisan environmental research organization in Washington. “You don’t want to be controlling the wrong thing.”

Among the most surprising of Dr. Guttikunda’s observations: In some cities, as vehicle traffic and tailpipe pollution declined, levels of one major smog-causing pollutant, ozone, actually shot up.

Dr. Guttikunda said the sharp rise was a real-life validation of a theory of atmospheric chemistry that says ozone — which is linked to asthma, heart disease and premature death — will increase, at least temporarily, as emissions of the tailpipe pollutants nitrogen oxide and sulfur dioxide go down.

“This is a theory that atmospheric chemists learn in class, but we haven’t seen it work in real time,” said Dr. Guttikunda.



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