Volcanic Eruptions: The Air Pollution Culprit

Volcanic eruptions can have a significant impact on air quality, with the potential to affect large populations thousands of kilometres away from the source. During an eruption, volcanoes emit a range of harmful gases, including sulphur dioxide, hydrogen fluoride, and carbon dioxide, which can cause a range of respiratory issues in humans and other animals, from asthma and bronchitis to eye and throat irritation. The sulphur dioxide and other gases can also combine with water vapour in the atmosphere to cause acid rain, which further affects both terrestrial and marine ecosystems. The ash produced by volcanic eruptions can also be harmful if inhaled, and the particles can remain suspended in the atmosphere for days to weeks, travelling vast distances. While volcanic carbon dioxide emissions are dwarfed by human-caused emissions, very large volcanic eruptions can still inject significant amounts of this greenhouse gas into the atmosphere, potentially contributing to global warming.

Ash and lava

Ash is a type of particulate matter that is released into the air during volcanic eruptions. The extent of an ash cloud's spread depends on factors such as particulate size, wind speed and direction, and eruption type. Finer ash particles can travel further and be carried by winds over thousands of miles, posing hazards to communities located far from the volcano. Aircraft are particularly vulnerable to ash clouds, as they can cause engine failure and damage flight control systems. Ashfall can also contaminate water supplies, damage buildings and infrastructure, and harm vegetation.

In addition to physical damage, volcanic ash can cause respiratory issues and eye irritation, especially in vulnerable individuals such as children, the elderly, and those with pre-existing lung conditions. The ash may contain sulphuric and other acids, increasing its irritancy on airways. Hydrogen fluoride, a highly reactive and toxic gas, can be absorbed into ash particles, impairing the surrounding biosphere when it comes into contact with the Earth's surface.

Lava, on the other hand, does not directly contribute to air pollution in the same way as ash. However, during certain types of volcanic eruptions, such as the Plinian eruption, lava bombs are ejected and can travel miles from the volcano. Lava domes can also form during eruptions, producing umbrella-like ash clouds that reach significant heights and speeds.

The interaction between lava and the surrounding environment can have indirect effects on air quality. For example, lava flowing into the ocean during an effusive eruption can release large amounts of sulphur dioxide and other gases into the lower atmosphere, leading to acid rain and air pollution. The specific composition of the lava and its interaction with water can influence the types and levels of gases released, potentially impacting air quality and human health.

While lava itself does not directly contribute to air pollution, it is important to consider its role in the overall volcanic eruption process, including the release of gases and the formation of ash and aerosol particles, which are the primary drivers of air pollution during volcanic events.

Sulphur dioxide and hydrogen fluoride gases

Sulphur dioxide (SO2) is one of the most common gases released during volcanic eruptions. It is a colourless gas with a pungent odour that irritates the skin, eyes, nose, and throat. Exposure to high concentrations of SO2 can cause immediate irritation of the nose and throat, eye irritation, and skin irritation within minutes. Sulphur dioxide is hazardous to human health and has been recorded downwind of many volcanoes, with the highest concentrations often seen close to persistently degassing volcanoes. For example, during an episodic increase in activity at Kilauea, Hawaii, in 1996, ambient concentrations of SO2 in a tourist car park rose to 4.0 ppm, nearly ten times higher than the USA's 3-hour concentration guideline.

SO2 emissions contribute to air pollution downwind of a volcano. At Kilauea volcano in Hawaii, high concentrations of sulphur dioxide produce volcanic smog (VOG), causing persistent health problems for downwind populations. During very large eruptions, SO2 can be injected to altitudes greater than 10 km into the stratosphere, where it is converted to sulfate aerosols. These aerosols reflect sunlight, contributing to a cooling effect on the Earth's climate and playing a role in ozone depletion.

In addition to its direct impacts on human health and climate change, SO2 also contributes to acid rain. When SO2 is introduced to water vapour in the atmosphere, it undergoes a chemical reaction to form sulphuric acid (H2SO4), which falls as acid rain. Acid rain expelled over land can have detrimental effects on terrestrial ecosystems and organisms, including humans.

Another gas released during volcanic eruptions is hydrogen fluoride (HF). Hydrogen fluoride is a highly soluble halogen that rapidly dissolves in water droplets within volcanic plumes or the atmosphere, potentially contributing to acid rain. In an ash-producing eruption, ash particles are often coated with hydrogen fluoride. Exposure to hydrogen fluoride can have severe detrimental effects on the respiratory systems of humans and other animal species.

Carbon dioxide and other gases

Carbon dioxide is lighter than other expelled gases, but it is heavier than air. This means that carbon dioxide expelled during volcanic eruptions sits lower in the atmosphere. High concentrations of carbon dioxide remain close to the Earth's surface, trapped under a heavier barrier of air, and are unable to diffuse upward into the higher atmosphere.

Carbon dioxide is a greenhouse gas and is the primary gas blamed for climate change. While the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming, it has been proposed that intense volcanic releases of carbon dioxide in the deep geologic past caused global warming and possibly some mass extinctions. This is a topic of scientific debate.

Volcanic eruptions can inject significant amounts of carbon dioxide into the atmosphere. The 1980 eruption of Mount St. Helens, for example, vented approximately 10 million tons of carbon dioxide into the atmosphere in only 9 hours. However, it is important to note that human activities now far exceed volcanic emissions of carbon dioxide. For instance, in 2010, human activities emitted 35 billion metric tons of carbon dioxide, which is about 80 to 270 times larger than the annual global volcanic carbon dioxide emission estimates.

In addition to carbon dioxide, volcanoes emit other gases, including sulphur dioxide and hydrogen fluoride, which can have severe impacts on both human health and the environment. Sulphur dioxide, for instance, can cause irritation of the nose, throat, eyes, and skin, and when it is introduced into water vapour in the atmosphere, it causes acid rain on a global scale. Hydrogen fluoride also poses a threat to the respiratory systems of humans and animals.

Acid rain

Volcanic eruptions can cause air pollution by releasing large quantities of sulphuric acid into marine and terrestrial ecosystems. The sulphuric acid in the rain expelled over land affects large populations of land-based organisms, especially humans. The introduction of sulphur dioxide to water vapour in the atmosphere causes acid rain on a global scale.

The 1980 eruption of Mount St. Helens in Washington state, which killed 57 people, released approximately 10 million tons of carbon dioxide into the atmosphere in just 9 hours. The eruption also resulted in an international pollution event, with 520 million tons of ash migrating eastward across the United States in three days and reaching the rest of the world in 15 days.

The 1991 eruption of Mount Pinatubo and the 1783-1784 Laki fissure eruption in Iceland are other examples of volcanic eruptions causing acid rain. The Laki eruption released 120 million tons of sulphur dioxide, killing thousands across Europe and affecting farm output. The Mount Pinatubo eruption, on the other hand, released a much smaller amount of sulphur dioxide (approximately 20 million tons) but still caused regional cooling in Europe and North America.

Volcanic acid rain typically contains hydrochloric acid and sulphuric acid, which form from the plume gases hydrochloric acid and sulphur dioxide. The formation of acid rain from volcanic eruptions can be summarised as follows: sulphur dioxide emitted from the volcano reacts with oxygen and moisture in the atmosphere to produce vog (volcanic smog) and acid rain. Acid rain can contaminate drinking water sources and damage vegetation, as well as cause health problems, especially for the elderly, infants, and those with respiratory and cardiovascular conditions.

Health impacts and safety concerns

Volcanic eruptions can have severe health impacts and safety concerns. Firstly, volcanic eruptions release harmful gases, such as sulfur dioxide, hydrogen sulfide, hydrogen halides, and carbon dioxide. These gases can cause global cooling, acid rain, and air pollution, leading to respiratory issues and irritation of the eyes, skin, and mucous membranes. High concentrations of carbon dioxide can result in headaches, dizziness, increased heart rate, breathing difficulties, unconsciousness, and even death. Additionally, volcanic ash can be abrasive and corrosive, causing eye and skin irritation and posing risks to those with respiratory ailments.

The health effects of volcanic air pollution can be felt by populations thousands of kilometers away and can last for days, decades, or even centuries. During an eruption, it is crucial to prioritize sanitary conditions for evacuated communities and monitor for infectious disease outbreaks. Volcanic gases are often odorless and invisible, making it challenging to avoid exposure. To protect oneself, individuals can wear respirators, carry medication, and follow local guidance and asthma action plans.

The impact of volcanic pollution extends beyond human health, affecting animals, plant life, marine ecosystems, and infrastructure. Toxic and harmful pollutants can damage or destroy vegetation and disrupt water treatment facilities. Additionally, volcanic activity can release halogens such as fluorine, chlorine, and bromine, which can contribute to acid rain and further environmental degradation.

Volcanic eruptions can also inject enormous amounts of carbon dioxide into the atmosphere, contributing to climate change. While human emissions of carbon dioxide currently dwarf those of volcanic eruptions, large explosive eruptions can release significant amounts of carbon dioxide in a short period. For example, the 1980 eruption of Mount St. Helens emitted approximately 10 million tons of carbon dioxide in just 9 hours.

The health and safety concerns associated with volcanic eruptions are diverse and far-reaching. The release of harmful gases, ash, and pollutants can impact humans, animals, and the environment, underscoring the importance of preparedness, monitoring, and protective measures to mitigate the potential risks posed by volcanic activity.

Frequently asked questions