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Greenhouse Gases


Pandemic experiments prove CO₂ monitoring networks provide real-time emission information

Real-time monitoring shows emissions fell in the Los Angeles and DC-Baltimore areas

by Katherine Bourzac
June 10, 2021 | A version of this story appeared in Volume 99, Issue 22


A photo of cars on a freeway in Los Angeles.
Credit: Vince360/Shutterstock
A decrease in traffic during pandemic lockdowns in April 2020 was a major reason CO2 emissions fell during that time in places like Los Angeles.

In April 2020, during the height of lockdowns designed to slow the spread of SARS-CoV-2, carbon dioxide emissions in the Los Angeles and Washington, DC–Baltimore areas fell by about 30% relative to the 2 previous years (Geophys. Res. Lett. 2021, DOI: 10.1029/2021GL092744). The data come from CO2 sensor networks established in the two regions by researchers at the Jet Propulsion Laboratory and the National Institute of Standards and Technology (NIST).

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A previous study measured the same drop in CO2 emissions in the San Francisco Bay Area during that region’s shelter-in-place order (Geophys. Res. Lett. 2020, DOI: 10.1029/2020GL090037). In all three cases, a decrease in passenger-vehicle traffic appears to have been the biggest reason for the reductions, which have since been reversed as people again ventured out of their homes.

These transient but dramatic emission changes gave chemists an opportunity to demonstrate the capabilities of their CO2 monitoring networks. Urban CO2 emissions are typically tallied indirectly each year using indicators, like gasoline sales, that don’t detect emission changes from day to day or week to week. The pandemic-era studies show that sensor networks that directly measure changes in CO2 concentration in cities can make information available much more rapidly—in near real time, says NIST’s Kimberly Mueller, one of the new study’s authors. “We’re trying to get data that could be useful for cities and city stakeholders,” she says.


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