Natural Air Pollutants: The Unseen Threat

Air pollution is a mix of hazardous substances from both human-made and natural sources. Natural sources of air pollution include wind-blown dust, wildfires, and volcanoes. Wildfires release smoke and ash into the atmosphere, while volcanoes emit ash, gases, and methane. Natural sources of air pollution can have significant impacts, but they do not usually create ongoing pollution problems like human-made sources.

Wildfires

PM2.5 accounts for most health effects due to air pollution in the US. Exposure to PM2.5 from wildfires has been associated with various adverse health effects, including respiratory diseases, asthma, lung disease, cardiovascular disease, and premature mortality. Individuals at greater risk of health effects from wildfire smoke include those with pre-existing cardiovascular or respiratory diseases, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status.

Wildfire smoke contains fine particles, also known as PM2.5, and coarse particles, known as PM10-2.5. According to Vicente et al. (2013) and Groβ et al. (2013), wildfire smoke is composed of approximately 90% fine particles, with a small percentage of coarse particles. These coarse particles are primarily generated from mechanical operations such as construction and agriculture.

The health effects of wildfire smoke exposure have been extensively studied, and the evidence demonstrates a clear relationship between exposure to fine particle pollution and various adverse health outcomes. While individual wildfire events may be short-lived, lasting only days or weeks, the health impacts can be significant and may result in increased hospital admissions, particularly for at-risk individuals.

As the world warms, air pollution from wildfires is expected to surge, posing serious risks to human health through transboundary air pollution. The recent WMO report used satellite data and ground-based monitoring to track the spread of air pollution during the 2021 summer fire season in North America and Russia. It found that PM2.5 levels spiked over western North America, reaching several times the level recommended by the World Health Organization.

Some countries have made progress in combating wildfires. For example, Indonesia experienced a series of wildfires in 2015 that impacted the health of thousands of people and caused significant economic losses. The Indonesian government is now working with local communities to promote alternative methods for clearing land without resorting to fires and is focusing on restoring degraded landscapes.

Volcanic eruptions

Volcanoes emit a variety of gases and particles during eruptions, including sulphur dioxide (SO2), hydrogen fluoride (HF), carbon monoxide (CO), water vapour, ash, and volcanic smog, or "vog". Sulphur dioxide and hydrogen fluoride are particularly harmful to humans and animals, damaging the respiratory system and posing lethal risks upon exposure. Sulphur dioxide also contributes to acid rain on a global scale. The Kilauea volcano in Hawaii, which has been erupting since 1983, is a notable example of a volcanic source of air pollution, releasing sulphur oxides that react with other atmospheric components to form fine particles and vog, a recognised health hazard.

The magnitude of volcanic pollution can be substantial, with the eruption of Mount St. Helens in 1980 releasing up to 3750 tons of sulphur dioxide daily. The resulting ash cloud migrated across the United States in three days and reached a global scale in 15 days. Similarly, the 1883 eruption of Krakatau in Indonesia produced an aerosol cloud that dispersed as far as New York, leading to conflagrations in New Haven.

The health risks associated with volcanic air pollution are significant. Inhaling volcanic gases and ash can be harmful, and many of these gases are odourless and invisible, making it difficult to avoid exposure. Volcanic ash can also cause practical challenges, as its weight may lead to structural issues and block air intake, limiting the amount of time individuals can remain indoors during heavy ashfall.

Decomposing organic matter

The rate of decomposition is influenced by various factors, including climatic conditions such as temperature, humidity, and precipitation. The quality and quantity of the soil also play a significant role, with clay content and water-holding capacity being important factors. The type of organic matter and the presence of certain organisms also impact the rate of decomposition. For example, in anaerobic conditions, bacteria break down organic matter, producing methane as a byproduct.

Anaerobic composting, or decomposition in the absence or limited supply of oxygen, involves collecting organic materials in pits and layering them with soil. The mixture is left undisturbed for around 6 to 8 months, allowing anaerobic microorganisms to flourish and decompose the organic matter. This process produces intermediates like hydrogen sulfide, methane, organic acids, and other substances with a pungent smell and potential phytotoxicity.

The decomposition of organic matter in soil can also help reduce pollutant concentrations through chemical dissipation and dilution, enabling microbial degradation. However, soils are facing a loss of organic matter due to factors such as population growth, urbanization, intensive farming, chemicalization, and fossil fuel combustion, which contribute to climate change.

While decomposing organic matter is a natural source of air pollution, it is important to note that natural sources typically do not create ongoing air pollution problems compared to human-made sources, such as vehicle emissions, fuel oils, and industrial processes.

Wind-blown dust

Dust storms, a specific phenomenon associated with wind-blown dust, can result in high levels of both PM10 and PM2.5 particles. While PM10 particles are larger and associated with coarse aerosol, PM2.5 particles are thinner and more hazardous to human health. It is important to understand the differences between these particle sizes and their respective health effects to address public safety concerns accurately.

The impacts of wind-blown dust extend beyond health risks. It can disrupt transportation on land, sea, and air, impact renewable energy systems, and transport pathogens and toxic substances. Additionally, wind erosion and dust emissions degrade agricultural lands, resulting in losses of nutrients and soil carbon essential for soil water retention.

To mitigate the effects of wind-blown dust, various dust control methods are employed, especially in regions susceptible to dust storms and high wind erosion, such as California. These methods include habitat restoration, managed vegetation, and tillage. While there is no universal solution, these approaches aim to reduce wind speeds, trap windblown soil particles, and minimize dust emissions.

Gases like methane

Methane emissions arise from both natural sources and human activities. Natural sources, such as wetlands, thawing permafrost, and decomposing organic matter in soils, account for about 40% of methane emissions. On the other hand, human activities, particularly in the agriculture, fossil fuel, and waste management sectors, contribute to the remaining 60% of methane emissions.

In the agriculture sector, methane emissions are associated with animal agriculture and livestock distribution. Oil and gas production, pipelines, refineries, and the storage and transportation of fossil fuels are also significant sources of methane leaks. Additionally, methane emissions can result from landfills, mining activities, and the decomposition of landfill waste.

The impact of methane on climate change is significant. While methane has a shorter lifespan in the atmosphere compared to carbon dioxide, it absorbs much more energy. This results in a higher global warming potential for methane. Reducing methane emissions is crucial to mitigate the rate of climate change and its associated health risks, including respiratory diseases, cardiovascular issues, and neurological disorders.

International efforts, such as the Global Methane Pledge, aim to reduce methane emissions across various sectors. Technologies like Bridger Photonics Gas Mapping LiDAR and NASA's Airborne Visible InfraRed Imaging Spectrometer (AVIRIS-NG) are being employed to detect and quantify methane leaks, helping industries identify and address the worst offenders. These collective efforts reflect a growing recognition of the urgent need to curb methane emissions and their detrimental effects on the environment and public health.

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