Air CO2 monitoring network in the urban areas of Puerto Naos and La Bombilla, La Palma, Canary Islands

Carbon dioxide (CO₂) is colorless, odorless and also heavier than air, which means it can accumulate at low elevations. At high concentrations, CO₂ can be hazardous and can cause asphyxiation by reducing the amount of oxygen available to breathe. In high concentrations, it can also irritate the eyes, nose, and throat. During the post-eruptive phase of Tajogaite eruption, high concentrations of air CO₂, up to 20% (200,000 ppmv), have been detected both outdoor and indoor of buildings at La Bombilla and Puerto Naos, which are located about 5 km from the eruption vent. Hazardous CO₂ concentrations were detected not only in the basements, but also on the ground floors and even inside of some upper floors buildings in Puerto Naos. In the case of La Bombilla, relatively high CO₂ concentrations were just observed on the ground floors. The spatial distribution of these hazardous indoor CO2 concentrations is not uniform throughout both populated areas (Hernández et al, 2022).

In order to study and assess this volcanic hazard, in both evacuated neighborhoods, an instrumental network for air CO₂ monitoring has been established by INVOLCAN in collaboration with the DGSE-GOBCAN and the Universities of the Azores (Portugal) and Düsseldorf Applied Sciences (Germany). The first CO₂ monitoring station was installed on 9 January 2022 and by the time being this network consists of 35 air CO₂ monitoring stations with different full scale (2 of 100%, 22 of 20%, 7 of 5% and 4 of 4%). In the case of La Bombilla the air CO₂ monitoring network consists of 10 different stations monitoring the indoor (7) and outdoor (3) CO₂ concentrations, respectively. The other 25 stations are located in Puerto Naos to monitor the indoor (21) and outdoor (4) ambient air CO₂ concentrations.

Observed outdoor CO₂ maximum and mean daily average concentrations > 5% (> 50,000 ppmv) and 0.9% (9,000 ppmv), respectively, have been recorded at Puerto Naos. However, indoor CO₂ monitoring at Puerto Naos have reached maximum and mean daily average concentrations about 20% (200,000 ppmv) and 12% (120,000 ppmv), respectively. In the case of La Bombilla, outdoor CO₂ measurements have reached maximum and mean daily average concentrations > 5% (> 50,000 ppmv) and about 2% (20,000 ppmv). Stations to monitor the indoor air CO₂ concentrations at La Bombilla were just installed (December 2022) and by the time being are recording maximum and mean CO₂ concentrations about 6% (60,000 ppmv) and 1.9% (19,000 ppmv), respectively. Most of the air CO₂ monitoring stations, both outdoor and indoor, shows that the daily averages of CO₂ concentrations from fifteen-minute data during the night are usually higher than during the day.

To mitigate the observed hazardous CO₂ concentrations some remediation techniques have been suggested, such as the installation of an indoor air CO₂ monitoring network with a larger number of stations and an automatic alert system for air CO₂ concentration inside residences with forced air ventilation systems.

Hernández P. A. et al., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7705, https://doi.org/10.5194/egusphere-egu22-7705, 2022.