Localization estimates. The ability to estimate emission source locations, referred to as "localization," is an important aspect of CMS. For example, operators can use these estimates to determine if a site visit is necessary to fix a fugitive leak. However, not all of the CMS vendors involved in this study provided localization estimates. Therefore, we apply the DLQ algorithm to the minute-frequency concentration data from each CMS solution and compare the resulting localization estimates from this algorithm. The DLQ algorithm infers localization estimates by comparing the CMS concentration measurements to forward simulated concentrations from each possible source. The source whose simulated concentrations most closely match the actual concentration measurements (assessed using correlation) is selected as the localization estimate. Note that this procedure imposes the assumption that one source is emitting at a time. We use the Gaussian puff atmospheric dispersion model to forward simulate, which accounts for time-varying wind conditions and is described in detail in Jia et al. .