Volcanic Eruptions: Pollution, Causes, And Impacts

Volcanic eruptions are a source of international pollution and a hazard. They can inject huge amounts of volcanic gas, dust, aerosol droplets, and ash into the stratosphere, causing air pollution. These emissions can have a detrimental impact on the climate, vegetation, human and animal health, and infrastructure. The most abundant volcanic gas is water vapour, which is harmless. However, volcanoes also emit significant amounts of carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen halides, and other toxic gases and particles. These gases and particles can cause acid rain, air pollution, and health issues such as irritation to the skin, eyes, nose, and throat, as well as more serious respiratory problems.

The impact of volcanic gases on human and animal respiratory systems

Volcanic eruptions release a mixture of gases, lava flows, and rock fragments (including ash and pumice) into the Earth's atmosphere. While water vapour is the most common volcanic gas and is harmless, volcanic emissions also include significant amounts of carbon dioxide (CO2), sulphur dioxide (SO2), hydrogen sulfide (H2S), and lesser amounts of hydrogen chloride (HCl), hydrogen fluoride (HF), and carbon monoxide (CO). These gases can have detrimental impacts on the respiratory systems of both humans and animals.

Sulphur dioxide, a colourless gas with a pungent odour, can irritate the skin and the mucous membranes of the eyes, nose, and throat in humans. Breathing in SO2 gas can also cause respiratory effects in animals. High concentrations of SO2 produce volcanic smog (VOG), which is a persistent health problem for downwind populations. During very large eruptions, SO2 can be injected into the stratosphere, where it is converted into sulfate aerosols that reflect sunlight and have a cooling effect on the Earth's climate.

Similarly, hydrogen sulfide is a colourless, flammable gas with a strong, offensive odour. At low concentrations, it is associated with a rotten egg smell, but at higher concentrations, it becomes odourless and toxic, causing irritation of the upper respiratory tract. Exposure to 500 parts per million (ppm) of H2S can cause a human to fall unconscious in 5 minutes and die in under an hour.

Carbon dioxide, while typically not life-threatening, can pose serious risks to people and animals when it accumulates in low-lying areas and reaches high concentrations under certain stable atmospheric conditions. Breathing air with more than 3% CO2 can lead to headaches, dizziness, increased heart rate, and difficulty breathing. At mixing ratios above 15%, carbon dioxide quickly causes unconsciousness and death.

Other gases, such as hydrogen chloride and hydrogen fluoride, contribute to acid rain, which can have detrimental effects on vegetation and agriculture. Acid rain can lower the pH of the soil, deterring plant growth and impacting crop yields. Additionally, volcanic emissions may raise fluoride concentrations in drinking water, potentially leading to fluorosis, which can damage teeth and bones.

The release of carbon dioxide and its effect on global warming

Volcanic eruptions can cause pollution by injecting huge amounts of volcanic gas, aerosol droplets, and ash into the stratosphere. While the ash falls rapidly and has little impact on climate change, volcanic gases like sulfur dioxide can cause global cooling, and volcanic carbon dioxide (CO2), a greenhouse gas, can promote global warming.

Carbon dioxide is a greenhouse gas and is the primary gas blamed for climate change. While contemporary volcanic eruptions have occasionally caused detectable global cooling of the lower atmosphere through the release of sulfur dioxide, the carbon dioxide released has never caused detectable global warming. This is because human activities emit 60 or more times the amount of carbon dioxide released by volcanoes annually. Since the Industrial Revolution, human emissions of carbon dioxide from fossil fuels and cement production have risen to about 35 billion metric tons per year, while volcanoes produce less than 1 billion metric tons.

However, it is important to note that volcanic activity has contributed to global warming over the course of geological time by producing significant amounts of carbon dioxide and other greenhouse gases. For example, geologists hypothesize that 250 million years ago, a large-scale, long-lasting eruption in Siberia likely raised global temperatures, causing one of the worst extinction events in Earth's history. While such eruptions are rare today, they have the potential to inject substantial amounts of carbon dioxide into the atmosphere.

Carbon dioxide in the atmosphere can lead to global warming through various mechanisms. One way is by increasing the K.E. (kinetic energy) of the troposphere through collisional relaxation of 15μ vibrationally excited CO2. Additionally, carbon dioxide dissolves into the ocean, reacting with water molecules to produce carbonic acid and increasing ocean acidity, a process known as ocean acidification. This has already had observable effects, such as the corrosion of marine snail shells. Furthermore, higher carbon dioxide levels can result in increased vegetation, which can contribute to cooling by providing more coverage over the Earth's surface.

In conclusion, while human activities are currently the primary driver of global warming through carbon dioxide emissions, volcanic eruptions can also contribute to global warming, particularly over geological timescales.

Sulphur dioxide's conversion to sulphuric acid aerosol and its cooling effect

During a volcanic eruption, a mixture of gases and particulates are expelled. One of the gases released is sulphur dioxide (SO2), which is a precursor gas. When sulphur dioxide is released into the stratosphere, it can be converted to sulphuric acid aerosol. This conversion is important as it has a cooling effect on the Earth's atmosphere.

Sulphur dioxide is a toxic gas that is harmful to humans and animals. It is dangerous to the respiratory system and can be lethal to plant life over a long period of time. When sulphur dioxide is released during a volcanic eruption, it rises into the stratosphere. In the stratosphere, sulphur dioxide is converted to sulphuric acid aerosol through a reaction with water vapour. This reaction typically occurs in clouds, where the water vapour and sulphur dioxide undergo an oxidation reaction to form gaseous sulphuric acid and various salts.

The sulphuric acid aerosol particles formed through this process are very small, with a diameter of about 0.1 to 1.0 micrometres. These microscopic liquid droplets or fine solid particles are then dispersed through atmospheric circulation. The sulphuric acid aerosol particles can remain in the stratosphere for up to seven years, reflecting radiation from the Sun back into space and causing a cooling effect on the Earth's lower atmosphere or troposphere.

The conversion of sulphur dioxide to sulphuric acid aerosol has been observed following major volcanic eruptions, such as the 1991 eruption of Mount Pinatubo in the Philippines. This eruption injected a significant amount of sulphur dioxide into the stratosphere, which converted to sulphuric acid aerosol and contributed to a global cooling effect. The cooling impact of these aerosol particles was noticeable even amidst rising human greenhouse gas emissions and the occurrence of an El Nino event during the study period following the eruption.

The emission of metal pollutants and their impact on the environment

While volcanoes are a natural source of metal pollutants, human activity is the primary cause of metal pollution. Metal pollutants from volcanoes derive from the molten rock that ascends from the mantle through the asthenosphere to the Earth's crust. During an eruption, large amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. These emissions can have severe detrimental impacts on the environment, including the quality of the air, soil, and water.

Volcanic soil and ash can contain various metals, including Fe, Mn, As, Pb, Zn, and Li. While Fe, Mn, and As may be derived from human activities, Pb, Zn, and Li may have anthropogenic sources. The presence of Pb and Zn in the soil and ash of the Changbai Mountain Nature Reserve in China, for example, has been linked to increasing tourism and vehicle traffic in the area. Zn has been found in automobile exhaust, tires, engines, fuels, and lubricants, which can be discharged into the environment and contribute to soil pollution.

Volcanic eruptions can also emit environmentally reactive, volatile metal pollutants such as selenium (Se), cadmium (Cd), and lead (Pb). These metal pollutants can accumulate in the soil, rain, snow, and plants in the immediate vicinity of active volcanic vents, and their presence has been detected in airborne particles or adsorbed to ash downwind. The 2018 eruption of Kīlauea in Hawai'i produced an exceptionally high discharge of metal pollutants, providing an opportunity to track their deposition. Studies have shown that volatile metal pollutants can be depleted in the plume up to 100 times faster than refractory species like magnesium and iron. This rapid wet deposition of complexes containing reactive and potentially toxic volatile metal pollutants may disproportionately impact localized areas close to the vent.

The emission of metal pollutants from volcanoes can have significant ecological and human health risks. Metal pollutants can affect the biodegradability of organic pollutants, making them less degradable and causing a double pollution effect. They can be taken up by plants through direct ingestion or absorption, posing hazards to the plant itself and any species within the food chain that consumes it. Metal pollutants can alter the properties of the soil, such as pH, colour, porosity, and natural chemistry, impacting soil quality and contaminating water sources. Additionally, the introduction of sulphur dioxide (SO2) into water vapour can lead to acid rain on a global scale, further damaging vegetation and agricultural lands.

The immediate health impact of volcanic air pollution on nearby populations

Volcanic eruptions can have detrimental immediate health impacts on nearby populations due to the release of harmful volcanic air pollution. The inhalation of volcanic ash and gases can pose serious respiratory hazards, with potential consequences ranging from the exacerbation of asthma symptoms to long-term damage to the respiratory system. Sulphur dioxide (SO2), a common volcanic gas, can have severe detrimental impacts when inhaled. It can also mix with water vapour in the atmosphere to form acid rain, which can affect vegetation and agriculture on a global scale.

The extent of the immediate health impact on nearby populations depends on various factors, including the proximity to the volcano, the magnitude of the eruption, and the composition of the emitted particles. During a volcanic eruption, ash columns can reach up to 50 kilometres in height, and the ash can disperse over distances of 100 to 1,000 miles. This wide reach means that volcanic air pollution can affect large populations, even those located thousands of kilometres away from the volcano.

The particle size, shape, surface area, and presence of leachable elements in the volcanic ash play a crucial role in determining its potential harm to human health. However, the health effects of volcanic ash inhalation are not yet fully understood due to limited evidence and varied methodologies in existing studies. Nevertheless, it is generally recognised as a probable respiratory hazard, and its impact can range from short-term to long-term health consequences.

Additionally, the dynamics of the eruption and the composition of the magma can influence the specific hazards posed to nearby populations. For example, the release of hydrogen chloride during a volcanic eruption can form hydrochloric acid when it comes into contact with water droplets. This strong acid contributes to acid rain, which lowers the pH of the soil, making it detrimental to plant growth and negatively impacting agricultural yields.

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