Cartoon demonstrating the domain-filling problem. The left panel shows the ideal case where each source sector’s spatial distribution and corresponding tracer are known a priori. In the right panel, representing the real-world case, the lack of a priori bottom-up flux inventory information for most of the measured atmospheric species used in this analysis is a problem. Emissions could have come from anywhere within the atmospheric footprint. There is no way to precisely and accurately identify a source within this area using just this individual footprint, although it may be possible to overcome this limitation given enough footprints with a wide enough variety of source sectors being overlapped. DOI: https://doi.org/10.1525/elementa.131.f4