Natural Air Pollutants: What Are Their Sources And Effects?

Air pollution is a pressing issue that poses a significant threat to global health and prosperity. It is caused by a combination of human-made and natural sources, with vehicles, fuel oils, natural gas, manufacturing, and power generation being the primary contributors to human-made air pollution. However, natural sources such as wildfires, volcanic eruptions, and decomposing organic matter also release hazardous substances into the air. These natural sources of air pollution raise the question: are there any natural forms of air pollutants?

Wildfires

The particles emitted by wildfires are primarily fine particles, known as PM2.5, which are less than or equal to 2.5 micrometres in diameter. These fine particles can be inhaled deeply into the lungs and have been linked to various adverse health effects, including respiratory and cardiovascular issues. Research has shown that exposure to wildfire smoke can worsen respiratory tract infections and has been associated with more severe cases of COVID-19 and even deaths.

The intensity and duration of wildfire events also play a role in their impact on air quality. While wildfires typically burn for a relatively short period (days to weeks), the smoke they produce can contain high concentrations of fine particles, leading to a rapid increase in air pollution levels. This sudden spike in pollution can have acute health effects, particularly for vulnerable individuals with pre-existing respiratory or cardiovascular conditions.

In addition to the immediate health risks, the cumulative impact of wildfires on air quality over time can be significant. Repeated exposure to wildfire smoke, especially for individuals living in areas prone to wildfires, can have long-term consequences for respiratory and cardiovascular health. The frequency and severity of wildfires are also influenced by climate change, creating a vicious cycle where wildfires contribute to climate change through air pollution, and the resulting extreme weather conditions further increase the risk of wildfires.

To mitigate the impact of wildfires on air quality and human health, it is crucial to develop strategies for wildfire prevention, early detection, and effective response. This includes implementing land management practices that reduce the risk of wildfires, such as controlled burns and fuel reduction techniques. Additionally, improving air quality monitoring systems and public health measures can help protect vulnerable populations during wildfire events.

Volcanic eruptions

Volcanoes emit a range of gases, including sulphur dioxide (SO2), hydrogen fluoride (HF), carbon monoxide (CO), and water vapour, which accounts for about 80% of the gases emitted. These gases can have detrimental effects on human health, particularly the respiratory system. Sulphur dioxide and hydrogen fluoride exposure can severely damage the respiratory systems of humans and other animals. Additionally, sulphur dioxide reacts with water vapour in the atmosphere to produce acid rain, causing further environmental harm.

The amount of sulphur dioxide released during volcanic eruptions can be substantial. For example, the 1980 eruption of Mount St. Helens released up to 3750 tons of sulphur dioxide per day, leading to an international pollution event. The Kilauea volcano in Hawaii, which has been erupting since 1983, is another example of a significant source of volcanic air pollution. The sulphur oxides released by Kilauea react with sunlight, atmospheric gases, and aerosols, forming fine particles that create volcanic smog, or "vog," recognised as a health hazard.

The impact of volcanic air pollution can be immediate and far-reaching, affecting people and the environment hundreds of miles away. It is essential to follow local guidance during volcanic eruptions to minimise exposure to these harmful pollutants and protect health.

Gases from decomposing organic matter

Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars, and mineral salts. It is a gradual process that has been taking place in nature since life first appeared on Earth. The speed of decomposition varies based on factors such as temperature, humidity, and season. For instance, warmer temperatures increase the rate of decomposition, while colder temperatures decrease it.

Decomposition can be categorised into two types: aerobic and anaerobic. Aerobic decomposition occurs in the presence of oxygen, where living organisms that require oxygen to survive feed on the organic matter. They use nitrogen, phosphorus, some carbon, and other nutrients. Carbon serves as a source of energy for these organisms and is released as carbon dioxide (CO2).

On the other hand, anaerobic decomposition occurs in the absence of oxygen. This can happen when a body is buried in organic material, and oxygen cannot reach it. This process, known as putrefaction, produces unpleasant odours due to the presence of hydrogen sulfide and other reduced organic compounds containing sulfur, such as mercaptans. The organic compounds are broken down by organisms that do not require oxygen, and they use nitrogen, phosphorus, and other nutrients to develop cell protoplasm. This process results in the release of organic acids, ammonia, and methane (CH4).

The process of anaerobic decomposition involves multiple steps and different types of organisms. Firstly, fermentation breaks down organic matter into simple fatty acids and CO2. Then, other organisms convert these fatty acids into more CO2 and H2. Finally, methane-generating bacteria, called methanogens, metabolise these substrates to produce methane as a byproduct.

Both types of decomposition play a crucial role in the nutrient cycle, recycling finite matter within the biosphere. They also influence the productivity of photosynthetic plants by mineralising or immobilising nutrients during the process.

Wind-blown dust

Air pollution is a mix of hazardous substances from both human-made and natural sources. Natural sources of air pollution include smoke from wildfires, ash and gases from volcanic eruptions, and gases like methane emitted from decomposing organic matter in soils.

One of the natural sources of air pollution is wind-blown dust. Wind-blown dust is a result of dust emitted from loose soils or disturbed natural lands by wind action. Weather conditions, the natural environment, and human activities can all contribute to the creation of wind-blown dust. Wind-blown dust is of particular concern in agricultural lands and semiarid to arid regions with loose sediments and flat, poorly vegetated land prone to wind erosion. Wind erosion and dust emissions degrade productive agricultural lands, resulting in losses of nutrients and the fine fractions of mineral soil and soil carbon responsible for soil water retention.

Additionally, wind-blown dust can menace transportation on land, sea, and air; disrupt renewable energy systems; and transport pathogens and toxic substances. It can also have economic impacts, such as costs for farmers to replace lost nutrients in the soil and underestimations of the actual impact of dust on highway safety due to inconsistent recording practices.

To mitigate the effects of wind-blown dust, various dust control methods are employed, taking into account local soil properties, topography, and meteorology. Public education is also important, as individuals should be advised to take precautions to avoid exposure to wind-blown dust, similar to the precautions taken during other strong air pollution episodes.

Agricultural burning

Air pollution is a mix of hazardous substances from both human-made and natural sources. While natural sources of air pollution include wildfires, ash and gases from volcanic eruptions, and gases like methane emitted from decomposing organic matter in soils, agricultural burning is a human-made source of air pollution that significantly contributes to poor air quality.

In India, for example, agricultural burning is a recurring issue due to the tight schedule of the harvest-to-sowing transition under the predominant rice-wheat rotation cropping system in northwestern India. However, countries like India are working to reduce air pollution from agricultural burning. The Climate and Clean Air Coalition works with countries and regional networks to promote alternatives to field burning. In India, the coalition provides farmers with information and assistance to access alternatives to crop fires, using satellites to monitor fires and track their impact, supporting policy interventions, and subsidizing farmers. For example, in Punjab, the coalition and the UN Food and Agriculture Organization (FAO) are looking at ways to turn crop residue that would otherwise be burned into a renewable fuel source.

To reduce the public health and welfare impacts of using burning in support of agricultural production, the AAQTF Agricultural Burning Policy recommends that states and tribes adopt a Smoke Management Program (SMP). The SMP is implemented through an Agricultural Burning Manager (ABM) who is responsible for managing agricultural burning at the state, local, or tribal level. The policy is founded on two basic principles: allowing the use of fire as an accepted management practice to maintain agricultural production, and protecting public health and welfare by mitigating the impacts of air pollution emissions on air quality and visibility.

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