Figure shows results from studies in the review that reported city-level CH4 emissions rates derived from TD measurements and disambiguated between major source types; methods used to attribute emissions are listed in S2. We extracted the studies' reported emissions rates and proportional contributions from these sources. The granularity of disambiguation differed between the studies depending on the measurement and attribution methods used; some studies only disambiguated between thermogenic and biogenic emissions, whereas others estimated emissions from landfills as a proportion of biogenic and total urban emissions. Therefore, we use a single category in Figure that encompasses all biogenic emissions to avoid potential issues in understating the importance of landfills across the estimates from the studies. Notably, landfills were generally responsible for most biogenic emissions in studies that separated landfill from other biogenic emissions (e.g., . Additional details on the data extraction and preparation for Figure are in S1. Figure . City/regional-level CH4 emissions rates by major source type reported in the studies. The abbreviations for cities/urban regions following the references on the y-axis are SFBA -San Francisco Bay Area, NY -New York, LA -Los Angeles, BOS -Boston, WSH, DC -Washington, District of Columbia, BLT -Baltimore, PHI -Philadelphia, IND -Indianapolis, PRV -Providence. The fossil fuel estimates in are associated with natural gas combustion/end-use only. Error bars show measurement uncertainty as reported in the studies. Figure indicates that CH4 emissions from fossil fuels dominate the emissions profile of most U.S. cities; however, we observe regional differences and exceptions. The mean fossil fuel percentage (FFP) derived from measurements in U.S. east coast cities is 74.6% (± 20.4%). FFPs reported by from TD measurements in five U.S. east coast cities were included in this estimate but are not shown in Figure because the study disambiguated the city-level CH4 flux but did not quantify emissions. The FFP relative to total city-level emissions differs between individual cities and may be affected by differences in natural gas infrastructure and the time of the year when measurements are performed. found lower FFPs in the summer than winter for some cities such as Philadelphia and Washington, DC, but less noticeable changes between seasons for others like Boston and New York. The U.S. east coast cities of Washington, DC, Baltimore, and Richmond (reported in Floerchinger et al. but not shown in Figure ) have larger contributions from biogenic emissions, specifically landfills, and thus have smaller FFPs relative to other cities in this region . The FFP does vary between studies for these cities - estimated that almost all measured CH4 emissions for Washington, DC and Baltimore were of fossil fuel origin. Differences in the FFP for the same city estimated across different studies may also be due to spatial variability in the area measured between studies.