Greenhouse gases in the tall tower of El Arenosillo station in Southwestern Europe: First-year of measurements

Carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) were measured at 10, 50 and 100 m in a tall tower located at El Arenosillo observatory (Southwestern Europe) from December 2021 to December 2022. Depending on the height, hourly averages varied between 418 ± 5 at 100 m and 422 ± 8 μmol mol−1 at 10 m for CO2, while CH4 varied between 1999 ± 30 nmol mol−1 at 100 m and 1986 ± 25 at 10 m and ~ 102 ± 19 nmol mol−1 for CO. A monthly variation with a common maximum in January–February was obtained while the minimum was found in June for CH4 and CO, whereas the minimum for CO2 was in August. The seasonal daily patterns showed a maximum between 5:00 and 10:00 UTC while the minimum was observed at 15:00–18:00 UTC. The daily variations are controlled by atmospheric stability, photochemical activity and vegetation influence, among other factors. The CO2 gradient was strongly conditioned by the photosynthesis, plant and soil respiration and vertical mixing with peaks higher than 19 × 10−2 μmol mol−1 m−1 at ~5:00 UTC in spring and autumn. The CH4 gradient, greater in winter and autumn (12–27 × 10−2 μmol mol−1 m−1) is affected by vertical stability, local emissions and photochemical activity while CO depicted small vertical gradients. A different behavior was found in the CO2 and CH4 gradients, for CO2 the 10–50 m gradient is higher than 50–100 m while CH4 was the opposite; which could reflect a lower CO2 surface layer than CH4. The observations at 100 m registered CO and CH4 peaks that were not recorded at 10 m, which could be associated with the arrival of a forest fire plume and potential CH4 fugitive emissions.