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A new study of 200 world cities shows the massive decline in air pollution that coincided with worldwide lockdowns at the onset of the COVID pandemic.

The study, from Wash University, showed that ground-level air pollution declined 30 percent in the first quarter of 2020, as compared to 2019.

As cited in St. Louis Public Radio:

“With fewer cars, trucks, and buses on the roads, air quality visibly improved in cities worldwide. In Los Angeles, the clear air offered a rare glimpse of the San Gabriel Mountains, while the normally thick haze of smog dissipated in New Delhi.

Washington University researchers have found concentrations of nitrogen dioxide, a harmful air pollutant that comes from burning fossil fuels, dipped dramatically during the first six months of 2020. Using satellite data, the team found the pollutant dropped by more than 30% on average worldwide, compared to 2019.”

Known as a spectrometer, the device measures how much light is reflected back toward the satellite at different wavelengths, allowing scientists to calculate the concentration of specific air pollutants in the atmosphere. They then feed the data into a mathematical model that accounts for weather conditions and nitrogen dioxide emissions, producing a detailed map of fluctuating nitrogen dioxide over time.

The results showed a “dramatic short-term change” in nitrogen dioxide concentrations worldwide during the pandemic, said Randall Martin, a Washington University engineering professor.

Certain technological advances, such as better fuel efficiency, have slowly reduced air pollution over time — but pandemic-related changes in transportation had a much larger and more immediate effect.

“The reductions that occurred during these COVID lockdowns are comparable to 15 years of technologically driven reductions globally,” said Martin, one of the study’s co-authors.