Volcanic Eruptions: Air Pollutants And Their Impact

Volcanic eruptions are a source of international pollution and a hazard to human health, vegetation, and infrastructure. They release a variety of gases and particulates, including water vapour, carbon dioxide, sulphur dioxide, hydrogen fluoride, hydrogen sulfide, hydrogen halides, and ash. These emissions can lead to air pollution, acid rain, and volcanic smog, which can have detrimental effects on the respiratory systems of humans and animals, as well as cause damage to vegetation and infrastructure. The scale of the impact can vary, affecting large populations thousands of kilometres away for extended periods, from days to decades or even centuries. The challenge lies in timely ash sample collection, analysis, and decision-making during an eruption when transportation and laboratory access may be disrupted.

Sulphur dioxide

SO2 is hazardous to human health, and concentrations of the gas have been recorded downwind of many volcanoes. For example, the Kilauea volcano in Hawaii has released high concentrations of SO2, leading to volcanic smog (VOG) and causing persistent health issues for nearby populations. The 1980 eruption of Mount St. Helens also resulted in an international pollution event, with up to 3750 tons of SO2 released into the atmosphere daily.

The effects of SO2 exposure can vary depending on an individual's sensitivity. The gas is generally perceived between 0.3-1.4 ppm, and its odour is easily noticeable at 3 ppm. At higher concentrations, SO2 can cause vomiting and loss of consciousness. For instance, in 1991, inhabitants of the Huemules valley near the Cerro Hudson volcano in Chile experienced vomiting and loss of consciousness due to intense sulphurous fumes.

SO2 also has a significant impact on climate change. During large eruptions, SO2 can be injected into the stratosphere at altitudes exceeding 10 km. In the stratosphere, SO2 is converted into sulphate aerosols, which reflect sunlight and contribute to a cooling effect on the Earth's climate. This conversion process also plays a role in ozone depletion.

To protect people from the dangers of SO2, several guidelines and advisory systems have been implemented by volcano observatories. These guidelines include evacuation protocols when SO2 levels exceed certain thresholds.

Hydrogen fluoride

Fluorine is highly soluble in water, and can therefore be quickly introduced into watercourses if the ash falls on wet ground or rain falls on it. This can lead to contamination of drinking water and soils, which is well-documented. In 2003, water tanks collecting rainwater in several localities downwind of the Nyiragongo volcano in the DR Congo were found to have fluoride concentrations up to 23 mg L-1, 15 times greater than the WHO guideline. In 1988, during the eruption of Lonquimay in Chile, thousands of people suffered from health effects associated with high concentrations of fine ash contaminated with fluoride.

In addition to the contamination of water, hydrogen fluoride can also have an impact on vegetation. High levels of fluoride have been found in vegetation at volcanoes in Etna, Italy; Kilauea, Hawaii; La Soufriere, Guadeloupe; and Furnas Caldera, Azores. In the Azores, high fluoride levels in lichen suggest that volcanic emissions may be responsible for high ground water fluoride levels, which have caused dental fluorosis in the local population.

Furthermore, hydrogen fluoride can impact animals, both through consuming affected vegetation and ash mixed with soil. In 1970, following the eruption of Hekla in Iceland, a combination of a poor hay crop and fluorosis from fluoride adsorbed on ash caused the deaths of 3% of adult sheep and 8-9% of lambs in areas where there was as little as 1 mm thickness of tephra. In 1995, the deaths of several thousand sheep following the eruption of Ruapehu in New Zealand were thought to be due to fluorosis, and isolated cases of fluorosis in cattle were reported following both the 1995 and 1996 eruptions.

While levels of primary volcanic HF at degassing volcanoes are rarely hazardous, the contamination of drinking water and soils by fluoride as a secondary effect is a significant concern.

Carbon dioxide

During volcanic eruptions, large amounts of gas, aerosol droplets, and ash are injected into the stratosphere. Carbon dioxide is released from the liquid portion of the magma (melt) as it rises towards the surface and pressure decreases. Even when magma does not reach the surface, carbon dioxide can escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems.

Volcanic carbon dioxide is a greenhouse gas that has the potential to promote global warming. While contemporary volcanic eruptions have not caused detectable global warming, carbon dioxide from intense volcanic activity in the deep geologic past may have contributed to global warming and possibly some mass extinctions.

In an average year, volcanoes release between about 180 and 440 million tonnes of carbon dioxide. While this gas is typically diluted to low concentrations and is not life-threatening, it can accumulate in low-lying areas under certain stable atmospheric conditions. Breathing air with more than 3% CO2 can lead to headaches, dizziness, increased heart rate, and difficulty breathing. Concentrations above 15% can cause unconsciousness and death.

Scientists have developed methods to quantify volcanic carbon dioxide emissions, combining measurements of volcanic fluxes of sulfur dioxide with C/S molar ratios to derive volcanic CO2 fluxes. Global estimates for annual volcanic carbon dioxide emissions range from about 0.13 to 0.44 gigatons, which is dwarfed by human carbon dioxide emissions, which were approximately 35 gigatons in 2010.

Volcanic ash

Volcanic eruptions are a significant source of air pollution, releasing a mixture of gases and particulates. One of the most well-known and hazardous types of air pollution associated with volcanic eruptions is volcanic ash.

The inhalation of volcanic ash can pose serious health risks, particularly for individuals with pre-existing respiratory conditions, children, older adults, and those with sensitive airways. Exposure to volcanic ash has been linked to respiratory irritation, triggering asthma attacks, and causing wheezing, coughing, and difficulty breathing. The small size of the ash particles allows them to reach deep into the respiratory system, potentially leading to long-term health issues.

The health impacts of volcanic ash inhalation are challenging to study due to the limited epidemiological evidence available. However, existing research suggests that the health effects of volcanic ash exposure may be similar to those of other types of particulate matter air pollution, such as outdoor smog or pollution from wildfires. By applying concentration-response functions (CRFs) and comparing them with outdoor air pollution health impact assessments (HIA), researchers can better understand the potential health consequences of volcanic ash inhalation.

To protect public health during volcanic eruptions, it is crucial to monitor and minimize exposure to volcanic ash. This includes following local authorities' instructions, wearing protective gear during cleanup, improving indoor ventilation, and using damp cleaning methods to prevent ash from becoming airborne again. Understanding the health risks associated with volcanic ash is essential for developing effective intervention strategies and guidelines to safeguard communities near volcanic activity.

Volcanic smog

Volcanic eruptions release a mixture of gases and particles into the atmosphere, which can have detrimental effects on the environment and human health. One of the most significant air pollutants associated with volcanic activity is sulphur dioxide (SO2), which is a colourless gas with a pungent odour. SO2 emissions can irritate the skin and mucous membranes of the eyes, nose and throat, and high concentrations of the gas can cause serious health issues. Sulphur dioxide also contributes to air pollution and acid rain, which further exacerbates its environmental impact.

Another pollutant that is often associated with volcanic eruptions is hydrogen fluoride (HF). This gas can be emitted during eruptions or seep out of cracks and fissures in the volcano's surface between major eruption events. Hydrogen fluoride dissolves rapidly in water droplets within volcanic plumes or the atmosphere, leading to acid rain. This acid rain can contaminate water supplies and harm both human health and the environment.

Vog poses several health and environmental risks. The acidic droplets in vog have corrosive properties similar to battery acid, and they can cause respiratory issues, watery eyes, sore throat, flu-like symptoms, and general lethargy. The aerosol particles in vog can scatter light, reducing visibility and creating hazards for transportation. Additionally, the sulphuric acid and other sulphates in vog contribute to air pollution and can negatively impact agriculture and water supplies.

The Kilauea volcano, located on the Island of Hawai'i, is a significant source of volcanic smog. Since its first eruption in 1983, Kilauea has continuously emitted large quantities of sulphur dioxide, with daily emissions ranging from 2,000 to 4,000 tons. The Pu'u 'Ō'ō eruption of Kilauea, which began in 1983, has released lava flows that have buried vast areas of land and added new land to the island. The volcanic gases from Kilauea, primarily sulphur oxides, react with sunlight, oxygen, and moisture to produce vog.

In summary, volcanic smog, or vog, is a hazardous air pollutant that forms when volcanic emissions interact with the atmosphere. It poses risks to human health, the environment, and transportation due to its corrosive nature and reduced visibility. The Kilauea volcano in Hawaii is a prominent source of vog, and its eruptions have had significant impacts on the surrounding communities and the island's geography.

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