Vehicle-based surveys are one of the most accessible techniques to measure spatially distributed sources in cities, which may account for the relatively high number of studies reporting this approach. Other methods such as flux chambers, surface enclosures, tracer releases, and mapping with handheld CH4 sensors were also used to measure distribution pipeline emissions . Measurements of ethane (C2H6) and δ 13 C were common methods in the studies to attribute the emissions to natural gas, although the number of samples taken for attribution relative to the total number of detected plumes is often very limited (e.g., . Moreover, natural gas and wastewater sources can mix, which results in ambiguous chemical signatures ( §3.2.1.2.). In general, there is significant uncertainty in attributing city-level estimates of leaks to different sources based on current methods.