Two reports challenge these findings: First, Williams et al. ( ) measured three "superemitting" manholes in Montreal. When scaled up to the city-level, they estimated that manholes (including sewers and storm drains) are the third largest CH4 source in Montreal, following active and historic landfills. The super-emitting manholes measured in were close to or within historical landfills in Montreal and it is possible that landfill gas is migrating into these manholes and escaping to the atmosphere, or that the manhole within the landfill is associated with a permanent leachate or run-off management system. The overlapping source signatures of δ 13 C for manholes and historic landfills reported in the study corroborate this hypothesis . This could have highbiased the city-level estimate and potentially misattributed the CH4 to wastewater when the source origin was the landfill. Second, de Foy et al. ( ) estimated total CH4 emissions from 61 cities and urban areas globally using TROPOMI and a 2D Gaussian fit method, including 19 U.S. cities and one Canadian city (Toronto). The pairing of this measurement platform and method does not permit identification of individual sources of CH4 emissions; however, de found that city-level emissions rates correlated with rates of untreated wastewater, inclusive of cities in high-income countries such as the U.S. and Canada. While this suggests that the collection and discharge of untreated wastewater may be an important source of emissions in cities in these countries, most studies in the review indicate that total city-level CH4 emissions are dominantly related to natural gas and landfills ( §3.1.2.).