ABSTRACT
Governments restricted mobility and effectively shuttered much of the global economy in response to the COVID-19 pandemic. Six San Francisco Bay Area counties were the first region in the United States to issue a "shelter-in-place" order asking non-essential workers to stay home. Here we use CO2 observations from 35 Berkeley Environment, Air-quality and CO2 Network (BEACO(2)N) nodes and an atmospheric transport model to quantify changes in urban CO2 emissions due to the order. We infer hourly emissions at 900-m spatial resolution for 6 weeks before and 6 weeks during the order. We observe a 30% decrease in anthropogenic CO2 emissions during the order and show that this decrease is primarily due to changes in traffic (-48%) with pronounced changes to daily and weekly cycles;non-traffic emissions show small changes (-8%). These findings provide a glimpse into a future with reduced CO2 emissions through electrification of vehicles.