A team of researchers from the National Museum of Natural Sciences (MNCN-CSIC) has verified that methane gas (CH4) disappears in underground environments with a high degree of humidity.
In this way, they act as sinks and help reduce the concentration of methane in the atmosphere. The study, published in the journal Nature Communications , could help develop cost-effective ways to mitigate emissions of this greenhouse gas and thereby reduce global warming.
After CO2, methane is the most abundant greenhouse gas on Earth. According to co-author Ángel Fernández-Cortés, a researcher at the MNCN and Marie Curie Fellow at the Royal Holloway (University of London), “there are many doubts about the diversity of existing methane sources and sinks, as well as their temporal evolution.
We have found that caves and other underground environments such as tunnels act as sinkholes. We also know that this can be extrapolated to other enclaves in the vadose zone (the one above the water table) with porous or fissured rocks connected to the outer atmosphere. “
They discovered this phenomenon while analyzing the behavior of carbon dioxide in relation to other gases such as radon or methane in the Altamira Cave. When studying the measurements, they detected that the atmospheric methane disappeared once the air from outside entered the cave , according to the MNCN researcher Sergio Sánchez-Moral.
To carry out their work, the research group has taken samples in different cavities of the vadose zone. They have monitored seven caves and other underground environments such as the Porto tunnels, and have taken samples at different times of the year and in diverse environments and ecosystems. With this they have verified that the concentration of methane gas decreases and even disappears completely. It is a very fast general oxidation process.
Until now, it was known that methane disappears from the atmosphere mainly due to photooxidation that, in the presence of water vapor, produces ultraviolet light in the troposphere, through the oxidation of methanotrophic bacteria in the soil and through its exit to the stratosphere. . “Now we know that underground environments also act as natural sinks for this gas.
In addition, we have verified that oxidation by methanotrophic bacteria, which eliminate it in the soil, is not the main elimination mechanism in underground environments , since the analyzes of the samples, which have been carried out at the Institute of Natural Resources and Agrobiology from Seville, also from the CSIC, show that they are not present in caves such as that of Castañar de Ibor (Cáceres), where the concentration of methane is zero throughout the year “, explains Soledad Cuezva, a researcher linked to the MNCN.
“We believe that the disappearance of the gas is related to a strong degree of ionization of the air in the cavities, but we still have to investigate what chemical reaction occurs so that it is eliminated. We must also quantify the effect to include it in global methane balances” , Fernández Cortés concludes.
