Periodical behaviour of air CO2 time series after Cumbre Vieja volcanic eruption

In the aftermath of the 2021 eruption of Cumbre Vieja volcano, a network of four low-cost air sensors was installed at four different sites in the village of Puerto Naos in La Palma, Canary Islands. These sensors measure CO₂, temperature, and relative humidity every one minute.

The measurements made between January and December of 2022 showed that all sensors frequently overpassed the 0.5 vol.%, defined by several organizations as the Permissible Exposure Limit (PEL) for safety in work environments. In addition, three of the sensors reached the instrument’s full scale (4.0 vol. %), a concentration above the STEL (short-term exposure limit) that can cause symptoms such as headache, weakness and breathing acceleration.

The Lomb-Scargle power spectral density estimate, obtained applying the plomb function of Matlab R2021a to the data, revealed diurnal cycles on the atmospheric CO₂ concentration time series in all monitored sites. All sites showed at least one cycle per day, with two of the sites having two cycles per day. One site, with an outdoor sensor, showed three cycles per day during the monitored period. Air temperature and relative humidity at the same sites showed similar periodicity, suggesting that the gas concentrations are correlated with the meteorological parameters. These observations, as far as we know, are the first to highlight the cyclic behaviour on volcanic air CO₂ time series.

This work was partially funded by FCT – Fundação para a Ciência e Tecnologia, under project SONDA - Synchronous Oceanic and Atmospheric Data Acquisition (PTDC/EME-SIS/1960/2020), and VOLRISKMAC II - Fortalecimiento de las capacidades de I+D+i para el desarrollo de la resiliencia frente a emergencias volcánicas en la Macaronesia (INTERREG MAC2/3.5b/328).