Street-level methane emissions of Bucharest, Romania and the dominance of urban wastewater.

Atmospheric methane (CH4) continues to increase, but there are multiple anthropogenic source categories that can be targeted for cost-effective emissions reduction. Cities emit CH4 the atmosphere from a mixture of sources, which include, not limited to, fugitive natural gas distribution systems, wastewater treatment facilities, waste-and rainwater networks, and landfills. Therefore, target mitigation measures, it is important locate quantify local urban prioritize opportunities in large cities. Using mobile measurement techniques, we located street-level leak indications, measured flux rates, determined potential origins (using carbon hydrogen stable isotopic composition along with ethane: ratios) Bucharest, Romania. We found 969 confirmed indication locations, where maximum mole fraction elevation (above background) was 38.3 ppm (mean = 0.9 ± 0.1 s.e.; n 2482). Individual indicator fluxes, derived using previously established empirical relation, ranged up around 15 metric tons yr-1 0.8 0.05, 969). The total estimated city emission rate 1832 (min 1577 t max 2113 yr-1). More than half (58%–63%) elevations were attributed biogenic wastewater, mostly venting storm grates manholes connecting sewer pipelines. Hydrogen ethane:methane ratios most useful tracers due similarities isotope between gas. annual city-wide estimate Bucharest exceeded Hamburg, Germany by 76% Paris, France 90%.