This is how sulfur dioxide is measured: the key gas to understand the evolution of the La Palma volcano

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The latest forecasts offered by the Volcanological Institute of the Canary Islands (INVOLCAN) indicate that the eruption of the La Palma volcano could last between 24 and 84 days. An essential forecast to know when you can start with the reconstruction of more than 100 hectares of the island that have been buried by the lava flows of the Cumbre Vieja.

One of the parameters considered key in which scientists are paying more attention is in the sulfur dioxide emissions. A decrease or an increase in the concentration of this gas in the atmosphere may indicate a relaxation or a rise in volcanic activity, respectively.

The latest data reported by INVOLCAN are “normal in an effusive eruption stage”, as they have published. And they understand between 8,000 and 10,500 tons of sulfur dioxide per day, very similar to those measured at the Fogo volcano (Cape Verde) in 2014. Before the eruption, La Palma had some fixed measurement units. But needs have changed radically since last Sunday and now it has mobile miniDOAS systems that roam the island.

Measuring gases

“Sulfur dioxide is naturally found within magma and is released with the eruption”, has told EL ESPAÑOL – Omicrono Arnau Folch, a volcanologist at the Barcelona Institute of Geosciences under the CSIC. “The main problem with this gas is that it directly affects air quality“He continues. This is especially important for the inhabitants of La Palma and the neighboring islands, who” will be able to experience the characteristic smell of rotten eggs “.

miniDOAS installed in a van

miniDOAS installed in a van


MiniDOAS are remote optical sensors capable of detecting the presence of sulfur dioxide, in the case of the volcanic eruption, and of many other trace gases such as ozone or nitrogen dioxide. They base their technology on Differential Optical Absorption Spectroscopy (DOAS) and it is used to measure the concentration of so-called trace gases in the air.

This device is capable of calculating the concentration of sulfur dioxide – and the other gases – in the atmosphere using nothing more than sunlight. When that light (radiation after all) hits the atmosphere with sulfur dioxide, the gas absorbs a certain radiation and the miniDOAS sensor is capable of capturing this difference with respect to a spectrum without polluting gases. Also providing a quantitative analysis of the trace gas analyzed.

Currently, INVOLCAN has mobile ground stations installed in vans that travel the island recording the amount of sulfur dioxide in the atmosphere and georeferencing it using GPS. In addition, they have also placed one in a helicopter that the Civil Guard has given to obtain aerial measurements.

By collecting all this data, scientists can create maps of the concentration of sulfur dioxide and, with them, learn about the volcano’s emissions and assess potential environmental risks.

MiniDOAS sensor installed in a Civil Guard helicopter

MiniDOAS sensor installed in a Civil Guard helicopter


“The sulfur dioxide is an indirect indicator of the amount of magma still accumulating in the volcano“and the experts use it as a ‘thermometer’ to make their predictions.” By looking at the eruptive rate, which is the amount of magma that comes out per unit of time, and the amount of gas, you can make estimates of the duration of the eruption. eruption”.

Causes acid rain

In addition to the discomfort of the smell and its negative effect on the respiratory tract, sulfur dioxide can produce acid rain. “When gas mixes with water in the atmosphere, it results in the chemical reaction of the well-known acid rain how damaging it is to vegetation, “says Foch.

“As the days go by, the emission of gases will increase”, which will provide more clues as to whether this type of rain can be produced. One of the most determining factors will be the windIf it is very intense or blows towards the sea, it will not affect the population or the vegetation.

“If the winds are looser and go towards the mainland it is possible that the concentration will increase and will have to be evaluated”, emphasizes the expert. The forecasts are aimed at sulfur dioxide reaching the Peninsula – entering the Region of Murcia – throughout Thursday or Friday and spread throughout the area, according to the simulation of a scientist who works in the European Copernicus emergency system. Although everything indicates that it will be in a concentration too low to cause problems.

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