COVID-19 Clears the Air (in one sense)

Nitrous oxide pollution in Wuhan, 2019 (top) and 2020 (bottom). Chinese New Year is responsible for the temporary decline shown on the top line. The quarantine associated with COVID-19 is responsible for the deeper and more persistent reduction this year. The coverage by the Independent correctly attributes the reduction of smog-forming NOx to the extensive quarantines in the region. It also mentions the concomitant reduction in greenhouse gases, but can leave readers with the incorrect impression that the maps depict the presence or absence of carbon dioxide.

The situation in China is reminiscent of the clearing of the air in Mexico City in 1985. At the time, 14 million people lived in the high-altitude (thin-air) bowl of the Valley of Mexico, kicking up fine-particle dust from the bed of Lake Tenochtitlan and more importantly contributing the exhaust of millions of tailpipes. Two successive earthquakes essentially stopped traffic and the air cleared. Many residents saw Popocatepetl and Iztaccihuatl for the first time in their lives. These icons of the city had not been visible from the city for decades -- nor have they been visible since. Despite many efforts to clear the air of Mexico City, an active population now numbering 22 million has not taken a long enough rest to do so as effectively as the enforced vacation of an earthquake or epidemic would do.



These phenomena are reminders that the air pollution we experience in and around many of the world's great cities is directly related to the choices we have made about work and transportation in those cities, and how we regulate emissions. Unfortunately, the clean air correlates not only with illness but also with economic dislocation, as illustrated by plummeting stock prices near the end of the same period (see below). That is to say, despite some successes at the margins, pollution remains tightly linked to economic progress.

Geographic Information Systems experts at Johns Hopkins University in Baltimore are providing constant updates to the distribution map. This is a graduated-circle map, in which a place is represented by a circle whose diameter is proportional to the square root of the phenomenon associated with that place. This is the March 1 map; click the link in the caption for updates.

As of 3/1/2020, 6:23:02 PM
Current map: JHU-CSSE