Abstract The COVID-19 pandemic led to widespread reductions in mobility and induced observable changes in atmospheric emissions. Recent work has employed novel mobility datasets as a proxy for trace gas emissions from traffic by scaling CO2 emissions linearly with those near-real-time mobility data. Yet there has been little work evaluating these emission numbers. Here, we systematically compare these mobility datasets to traffic data from local governments in seven diverse urban and national/state regions to characterize the magnitude of errors that result from using the mobility data. We observe differences in excess of 60% between these mobility datasets and local traffic data. We could not find a general functional relationship between mobility data and traffic flow over all regions and observe higher deviations from using such general relationships than the original data. Finally, we give an overview of potential errors that come from estimating CO2 emissions using (mobility or traffic) activity data. Future work should be cautious when using these mobility metrics for emission estimates.
What are different measures of mobility telling us about surface transportation CO2 emissions during the COVID-19 pandemic?