ALERTACO2 Project update: An extensive monitoring network for monitor and mitigate the CO2 hazard of indoor and outdoor air CO2 at the inhabited areas of Puerto Naos and La Bombilla, La Palma (Canary Islands)

As a result of the Tajogaite eruption (2021), La Palma island, anomalous volcanic CO₂ emissions were observed by the end of November 2021 in the neighborhoods of La Bombilla, Puerto Naos, and some banana plantations, where appear daily many dead fauna (insects, birds, lizards and small mammals), located at about 6 km southwestern from Tajogaite eruption vents. These urban areas, not directly damaged by lava flows, were included in the exclusion zone due to the strong volcanic-hydrothermal CO₂ concentrations (>5-20%). CO₂ enters into the homes and premises through hydraulic and electrical conduits and the vertical structure of the buildings itself, causing an accumulation of CO₂ indoor that reaches high or very high concentrations. CO₂ is an asphyxiating and toxic gas in very high concentrations, as it implies a corresponding reduction in the oxygen (O₂) content. Immediate evacuation of indoor spaces is recommended if the CO₂ concentration excedes 1.5% (15,000ppm).

During the last two years after the eruption, several institutions deployed indoor and outdoor own gas networks, to try to delimitate the CO₂ anomalies where CO₂ air concentration exceed hazardous thresholds, but with an insufficient number of CO₂ sensors (less than 100) to cover all homes, garages, basements and stores in real time. These studies aim to understand the dynamics of CO₂ emission to delimitate the CO₂ anomalies where CO₂ air concentration exceed the hazardous thresholds, and help the authorities’ decision-making of people's return to their homes and stores.  

The ALERTACO2 project, participated by IGN and INVOLCAN institutes, was financed by the Spanish Government with an amount of 3M€ during a period of 4 years (2023-2026), and has the goals of implementing a much more extensive network of CO₂ sensors (around 1,200 NDIR sensor developed by Sieltec Canarias) in real time in most of the building of both inhabited areas, the creation of a 24-hour monitoring room and an information and awareness campaign for the population about this volcanic hazard.

At the present time, 1294 sensors are installed (1,287 indoor and 7 outdoor), of which 147 are in La Bombilla and 1,133 in Puerto Naos and 7 moving stations and 7 outside these places. Each sensor has a color light code to indicate the CO₂ concentration (green, yellow, orange and blue if the sensor is not working), and a QR code to view the information remotely. Each sensor sends the data to the 24-hour monitoring room via a gateway installed at the roof of each building. Thanks to ALERTACO2, many families have been able to return to their homes in safety conditions since December 2023, because their homes average CO₂ concentrations were below 1,000 ppm.