Can We Detect Urban‐Scale CO 2 Emission Changes Within Medium‐Sized Cities?

The COVID‐19 pandemic resulted in a widespread lockdown during the spring of 2020. Measurements collected on a light rail system in the Salt Lake Valley (SLV), combined with observations from the Utah Urban Carbon Dioxide Network observed a notable decrease in urban CO 2 concentrations during the spring of 2020 relative to previous years. These decreases coincided with a ∼30% reduction in average traffic volume. CO 2 measurements across the SLV were used within a Bayesian inverse model to spatially allocate anthropogenic emission reductions for the first COVID‐19 lockdown. The inverse model was first used to constrain anthropogenic emissions for the previous year (2019) to provide the best possible estimate of emissions for 2020, before accounting for emission reductions observed during the COVID‐19 lockdown. The posterior emissions for 2019 were then used as the prior emission estimate for the 2020 COVID‐19 lockdown analysis. Results from the inverse analysis suggest that the SLV observed a 20% decrease in afternoon CO 2 emissions from March to April 2020 (−90.5 tC hr −1 ). The largest reductions in CO 2 emissions were centered over the northern part of the valley (downtown Salt Lake City), near major roadways, and potentially at industrial point sources. These results demonstrate that CO 2 monitoring networks can track reductions in CO 2 emissions even in medium‐sized cities like Salt Lake City. High‐density measurements of CO 2 were combined with a statistical model to estimate emission reductions across Salt Lake City during the COVID‐19 lockdown. Reduced traffic throughout the COVID‐19 lockdown was likely the primary driver behind lower CO 2 emissions in Salt Lake City. There was also evidence that industrial‐based emission sources may of had an observable decrease in CO 2 emissions during the lockdown. Finally, this analysis suggests that high‐density CO 2 monitoring networks could be used to track progress toward decarbonization in the future. High‐density CO 2 measurements provided constraints on emission reductions during the COVID‐19 lockdown CO 2 emissions across the Salt Lake Valley were reduced by ∼20% relative to 2019 during the first COVID‐19 lockdown The largest reductions in CO 2 were likely driven by reduced traffic, especially in downtown Salt Lake City