In the tall tower of the El Arenosillo station, located on the Atlantic coast of southwestern Europe, greenhouse gas observations began in November 2021. Carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) were measured at 10, 50 and 100 m; an initial study was conducted using the measurements from the first year, until 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 (Adame et al., 2024). 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 (Fig. 1).

Fig. 1. Temporal evolution of the daily averages of CO2 (a), CH4 (b) and CO (c) in the three heights (10 – orange line, 50 – green line and 100 m-blue line) from December 2021 to December 2022.

The seasonal daily patterns were also investigated, revealing a daily variation for the three gases with a peak between 5:00 and 10:00 UTC, while the minimum was observed at 15:00-18:00 UTC. These daily variations are controlled by atmospheric stability, photochemical activity and vegetation influence, among other factors.

Thanks to the availability of measurements at three heights, the average daily seasonal gradients could be analysed. The CO2 gradient was strongly conditioned by the photosynthesis, plant and soil respiration and vertical mixing; the CH4 gradient, greater in winter and autumn is affected by vertical stability, local emissions and photochemical activity while CO depicted small vertical gradients.

The observations at the 100 m level allowed the detection of the arrival of fire plumes, with peaks of CO, and even the impact of air masses enriched with methane, most likely associated with fugitive emissions. Ongoing studies are being conducted to enhance our understanding of the dynamics of greenhouse gases and to determine their trends.


Adame, J. A., Padilla, R., Gutierrez-Alvarez, I., Bogeat, J. A., Lopez, A., Yela, M. 2024. Greenhouse gases in the tall tower of El Arenosillo station in Southwestern Europe: First-year of measurements. Atmospheric Research, 107221. DOI: 10.1016/j.atmosres.2024.107221.