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On March 19, California was one of the first states to set mandatory stay-at-home restrictions in an attempt to slow the spread of COVID-19. Arizona and Nevada followed suit around April 1.

The Ozone Monitoring Instrument (OMI) on board NASA's Aura satellite provided data that indicate that these restrictions have led to about a 31% decrease in NO₂ levels in the Los Angeles basin relative to previous years.

NO₂, or nitrogen dioxide, is an air pollutant measured by OMI. The estimated reductions for other cities in the Southwest U.S. before and after the quarantine restrictions are 22% for the San Francisco Bay Area; 25% for San Diego and Tijuana, Mexico; 16% for Phoenix; and 10% for Las Vegas.

Nitrogen Dioxide (NO₂) Decreases Over American Southwest

The slider above shows satellite estimates of NO₂ from Aura’s Ozone Monitoring Instrument (OMI) as an average of March 25 through April 25. The left image shows the mean of the 150-day period from 2015 through 2019, while the right image shows the mean of the 30-day period for 2020. Credit: NASA

For more information on NASA's air quality research, visit https://aura.gsfc.nasa.gov.

The visual for this article and other regions can be downloaded from NASA's Scientific Visualization Studio.

For more information please contact:

Peter Jacobs
Public Affairs Officer
peter.jacobs@nasa.gov