Estimating Urban CH4 ${\text{CH}}_{4}$ Emissions From Satellite‐Derived Enhancement Ratios of CH4 ${\text{CH}}_{4}$, CO2 ${\text{CO}}_{2}$, and CO

Abstract Urban centers are an important source of anthropogenic methane emissions and the focus of recent policy efforts aimed at emission reductions. But, emissions from urban areas are poorly characterized except in the few cities with robust measurement infrastructure. Satellite measurements offer a means for monitoring urban emissions. We use colocated measurements of methane () and carbon monoxide (CO) from the TROPOspheric Monitoring Instrument (TROPOMI) and carbon dioxide () from the Orbiting Carbon Observatory 2 and Orbiting Carbon Observatory 3 (OCO‐2/3) to calculate :, :CO, and CO: enhancement ratios over 103 cities. We compare our enhancement ratios to those derived from ground‐based instruments in Los Angeles and find good agreement. Then, we combine our enhancement ratios with CO and inventories to calculate emissions and find good agreement with estimates from past studies. Finally, we compare our satellite‐based enhancement ratios to those computed from the bottom‐up globally gridded emission inventories, and we find significant differences between them. Combining results from the three enhancement ratios, we find EDGARv8 to best represent emissions in urban areas with mean errors of 34% compared to CAMS‐GLOB‐ANTv6.2 (based on EDGARv6.1), and CEDSv2021 with mean errors of 43% and 49%, respectively. These differences are largely driven by EDGARv8 changes in South‐Central and East Asia. We also find that EDGARv8 and HTAPv3 underestimate CO emissions by a factor of 2–5 for cities in Iran, Turkmenistan, and Argentina. Finally, we find that CO emissions are overestimated in some cities in Europe by a factor of 2.