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. The objective of this study is to derive methane(CH4) emissions from three landfills, which are found to be the mostsignificant CH4 sources in the metropolitan area of Madrid in Spain. Wederive CH4 emissions from the CH4 enhancements observed byspaceborne and ground-based instruments. We apply satellite-basedmeasurements from the TROPOspheric Monitoring Instrument (TROPOMI) and theInfrared Atmospheric Sounding Interferometer (IASI) together withmeasurements from the ground-based COllaborative Carbon Column ObservingNetwork (COCCON) instruments. In 2018, a 2-week field campaign for measuring the atmosphericconcentrations of greenhouse gases was performed in Madrid in the frameworkof Monitoring of the Greenhouse Gases Concentrations in Madrid (MEGEI-MAD) project.Five COCCON instruments were deployed at different locations around theMadrid city center, enabling the observation of total column-averagedCH4 mixing ratios (XCH4). Considering the prevalent wind regimes,we calculate the wind-assigned XCH4 anomalies for two opposite winddirections. Pronounced bipolar plumes are found when applying the method toNO2, which implies that our method of wind-assigned anomaly is suitableto estimate enhancements of trace gases at the urban level from satellite-basedmeasurements. For quantifying the CH4 emissions, the wind-assignedplume method is applied to the TROPOMI XCH4 and to the lowertropospheric CH4 / dry-air column ratio (TXCH4) of the combinedTROPOMI+IASI product. As CH4 emission strength we estimate 7.4 × 1025 ± 6.4 × 1024 molec. s−1 from the TROPOMI XCH4 data and7.1 × 1025 ± 1.0 × 1025 molec. s−1 fromthe TROPOMI+IASI merged TXCH4 data. We use COCCON observations toestimate the local source strength as an independent method. COCCONobservations indicate a weaker CH4 emission strength of 3.7 × 1025 molec. s−1 from a local source (the Valdemingómez wasteplant) based on observations from a single day. This strength is lower thanthe one derived from the satellite observations, and it is a plausibleresult. This is because the analysis of the satellite data refers to alarger area, covering further emission sources in the study region, whereasthe signal observed by COCCON is generated by a nearby local source. Allemission rates estimated from the different observations are significantlylarger than the emission rates provided via the official Spanish Register ofEmissions and Pollutant Sources.

atmospheric chemistry and physics

Quantification of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; emissions from waste disposal sites near the city of Madrid using ground- and space-based observations of COCCON, TROPOMI and IASI