The sulphur dioxide (SO2) emissions from a volcanic eruption in the Caribbean reached India April 16, 2021 sparking fear of increased pollution levels in the northern parts of the country and acid rain. Sulphur dioxide reacts with water to form sulphuric acid which can come down with rainfall. Volcanic “plumes can cause aviation and air quality hazards.
La Soufrière volcano on St Vincent Island in the West Indies started erupting on April 9 after spewing out lava into a dome and threatening to erupt since December 2020. The last time the volcano had erupted was in 1979. Of the 45 currently erupting volcanoes on Earth, La Soufriere is among those that worry volcanologists the most and this is because of its “explosive and erratic eruption style”. The volcanic eruptions that occurred on April 10 were energetic enough for the plumes to be recorded at a height of 20-km above the Earth’s surface by the Multi-Angle Imaging Spectro Radiometer instrument on NASA’s Terra satellite.
NASA scientists have found evidence for the entry of sulphate aerosol particles (precursors for sulphuric acid) in the stratosphere, the second layer of the Earth’s atmosphere. Scientists watch closely for emissions reaching the relatively dry stratosphere because particles last much longer and travel much farther than if they remain in the lower, wetter troposphere. This might be the reason that the particles have reached as far as India and will likely travel beyond to reach South East Asia. Volcanic emissions reaching the stratosphere can have a cooling effect on global temperatures. “The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulphur dioxide to sulphuric acid, which condenses rapidly in the stratosphere to form fine sulphate aerosols,” says the United States Geological Survey’s website.
“The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth’s lower atmosphere or troposphere,” it added. Bigger eruptions during the past century have caused a decrease in temperature of 0.27 degree Celsius or more on the Earth’s surface for up to three years.
“The current thinking is that a volcano needs to inject at least 5 teragrams of SO2 into the stratosphere to have measurable climate impacts,” explained Simon Carn, a volcanologist at Michigan Technological University in the United States.
La Soufrière has delivered around 0.4-0.6 teragram of SO2 into the upper atmosphere which is the highest-ever recorded after satellites started observing the Earth’s atmosphere in the mid 20th century. The amount of SO2 being vented out by the volcano could increase if the eruptions continue. NASA scientists also surmise that moderate eruptions are usually far greater in number than huge eruptions and could have a greater cumulative impact.