The ratios between TD and BU estimates of city-level CH4 emissions underpinning Figure 1 range from 0.7 to 4.9 after averaging the ratios reported in individual studies. The data allude to possible regional differences in the extent of the discrepancy between TD and BU estimates when grouped. The median ratio for the U.S. West Coast is the lowest of the four regions at 1.4, and the median ratio for U.S. Central is slightly higher than the U.S. West Coast at 1.6. Each of these regions have outliers at 2.9 for Los Angeles, CA and 4.9 for Houston, TX , respectively. Notably, both outliers for these regions were reported in studies that used satellites to estimate emissions. Oil and gas production in Houston, TX may explain the high ratio for this city relative to other cities. The U.S. East Coast has a higher median ratio than the other U.S. regions at 2.2 and notably larger ratio variability indicated by the lower and upper quartiles. Ratios for the U.S. East Coast range between 1.1 . We typically did not observe ratios this high for non-satellite studies. The high ratio reported in the later study may be related to the timing of the stationary sensor measurements in , which may have corresponded with increased CH4 emissions from natural gas sources in winter in Philadelphia, PA. Canada had the highest median ratio of all regions in Figure (3.4), but a small sample size limits further comparison; the ratio is based on three TD estimates for Canadian cities reported only in two satellite-based studies .