Table 3. Statistics from Surveys on Methane Enhancements from Natural Gas Sources Found in Each Citya.
| city name | high CH4 enhancement | medium CH4 enhancement | low CH4 enhancement | lowest CH4 enhancement | leak indications per 100 km calculated following Weller et al.8 (only accounting for high, medium, and low enhancements) | leak indications per 100 km calculated following Ars et al.15 (including the lowest enhancement category) | roads covered (km) | total roads within domain (km) |
|---|---|---|---|---|---|---|---|---|
| ≥7.6 ppm | 7.59 to 1.6 ppm | 1.59 to 0.2 ppm | 0.19 to 0.04 ppm | |||||
| Barcelona, Spain | 0 | 1 | 5 | 59 | 2 | 18 | 367 | 2171 |
| Birmingham, United Kingdom | 0 | 1 | 12 | 26 | 6 | 19 | 206 | 1121 |
| Bucharest, Romania | 8 | 36 | 384 | 881 | 60 | 183 | 715 | 2086 |
| Groningen, The Netherlands | 1 | 5 | 18 | 32 | 9 | 20 | 277 | 709 |
| Hamburg, Germany | 0 | 5 | 52 | 196 | 3 | 14 | 1576 | 4617 |
| Katowice, Poland | 0 | 5 | 38 | 39 | 4 | 8 | 1062 | 3889 |
| London, United Kingdom | 4 | 65 | 494 | 802 | 16 | 38 | 3615 | 18,397 |
| Munich, Germany | 0 | 1 | 2 | 20 | 2 | 18 | 129 | 2081 |
| Paris, France | 0 | 3 | 59 | 313 | 13 | 77 | 485 | 3394 |
| Swansea, United Kingdom | 0 | 3 | 17 | 37 | 8 | 23 | 244 | 745 |
| Toronto, Canada | 0 | 1 | 18 | 227 | 2 | 22 | 1110 | 5750 |
| Utrecht, The Netherlands | 1 | 5 | 19 | 162 | 5 | 40 | 472 | 757 |
a
Unique road kilometers covered calculated from GPS data and total road kilometers within domain from OpenStreetMap data. The leak indications per 100 km are reported as a range, with the lower end only accounting for large, medium, and small peaks (as common in previous US studies), while the upper end of the range includes the lowest peak category as well, as introduced by Ars et al.15