Finally, we note a number of limitations of the PDM as currently implemented. First, it assigns zero probability of combining adjacent naive events if their source estimates are different, meaning that errors in localization estimates can propagate to errors in duration estimates. Second, periods of information are subject to errors in the Gaussian puff dispersion model, which can result in naive events that occur during periods of no information (e.g., naive events I, III, and IV in Figure ). Third, the PDM assumes a single emission source for all emission events. The ability to localize multi-source emissions will be necessary for accurate CMS-based duration estimates on complex sites where this assumption breaks down, and methods to do so are currently under development.