Natural Air Pollutants: Sources And Impacts

Air pollution is caused by the release of gases, finely divided solids, and finely dispersed liquid aerosols into the atmosphere. These particles and gases can come from car and truck exhaust, factories, dust, pollen, mold spores, volcanoes, and wildfires. Natural sources of air pollution include organic compounds from plants, sea salt, suspended soils, and dust. Additionally, microbial decaying processes result in the natural release of gases, particularly methane gas.

Volcanic eruptions

One of the primary ways volcanic eruptions contribute to air pollution is through the emission of ash. Ash clouds formed during volcanic eruptions can disperse across vast distances, spreading fine particles that remain suspended in the air. The extent of the ash cloud's dispersal depends on factors such as particulate size, wind speed, wind direction, and the type of eruption. For example, the eruption of Mount St. Helens in 1980 released about 520 million tons of ash, which migrated across the United States in three days and reached around the world in 15 days.

Additionally, volcanic eruptions can emit toxic chemicals and particles that negatively impact human health. The United States Geological Survey (USGS) has stated that acid rain and air pollution from volcanic eruptions can pose persistent health problems for nearby populations. The ash and chemicals released during volcanic events may require the expertise of toxicologists and other specialists to evaluate their environmental and health impacts on surrounding areas.

Wildfires

Particulate matter, or PM, is the primary pollutant of concern in wildfire smoke. These particles are incredibly small, often measuring 2.5 micrometers or less in diameter. Due to their minuscule size, these particles can easily penetrate deep into the respiratory system, reaching the lungs and even entering the bloodstream. This intrusion of particulate matter can have severe health consequences, particularly for individuals with pre-existing cardiovascular or respiratory conditions, the elderly, children, pregnant women, and those engaged in outdoor work.

The health risks associated with exposure to wildfire smoke are well documented. Fine particles (PM2.5) account for approximately 90% of the total particle mass in wildfire smoke. These particles have been linked to various adverse health effects, including eye and lung irritation, exacerbation of respiratory and cardiovascular conditions, and an increased risk of heart attacks and strokes. The impact of wildfire smoke on human health is so significant that it has prompted the creation of guides to assist public officials and communities in mitigating its effects.

The size and intensity of wildfires have been increasing, and they now pose a substantial public health challenge. As wildfires become more frequent and severe, the resulting air pollution affects a broader geographic area and a larger number of people. This trend is particularly concerning for populations living near wildfire-prone regions or downwind of them. To protect themselves from the harmful effects of wildfire smoke, individuals are advised to stay indoors, close windows and doors, and use air conditioning with the recirculate function turned on. In areas with poor air quality, it is recommended to eliminate outdoor activities, especially strenuous exercise, to minimize exposure to harmful particulate matter.

Microbial decay

Air pollution is caused by solid and liquid particles, known as aerosols, and certain gases that are suspended in the air. These particles and gases can come from car and truck exhaust, factories, dust, pollen, mould spores, volcanoes, and wildfires.

The fungal community in polluted air was mostly comprised of saprotroph species, which thrive due to the abundance of nutrients supplied by apoptotic cells. The overall health risks posed by these microbes decrease significantly after 20 days, regardless of whether the air is polluted or not. This indicates that the biological effectiveness of these microbial communities is limited to a certain timeframe.

Air pollution has been linked to an imbalance in the human microbiota, which refers to the beneficial, neutral, and sometimes opportunistic microbes that are present in the human body. This imbalance can lead to an overgrowth of pathogens and a disruption in the production of beneficial metabolites, resulting in various health issues. For example, exposure to polluted air has been shown to cause pathological changes in the intestinal microbiota of both mice and humans, which can lead to allergies, respiratory diseases, and potentially severe acute respiratory syndrome (SARS) coronavirus infections.

Radioactive decay

Radioactive contamination is a natural cause of air pollution. Radioactive decay of contaminants produces ionizing radiation in the form of alpha, beta, gamma rays, and free neutrons. The degree of hazard posed by this radiation depends on the concentration of the contaminants, the energy of the radiation being emitted, the type of radiation, and the proximity of the contamination to organs of the body.

Radioactive contamination can be caused by natural or man-made sources. Natural sources include elements like uranium and thorium, and their decay products, which are present in rock and soil. Uranium mill tailings, for example, contain the radioactive element radium, which decays to produce the radioactive gas radon. To prevent radon from escaping into the atmosphere, uranium mill tailings are covered with a sealing barrier of material such as clay, and this is then covered by a layer of soil, rocks, or other materials to prevent erosion of the sealing barrier.

Radioactive contamination can occur through the release of radioactive gases, liquids, or particles. For instance, if a radionuclide used in nuclear medicine is spilled, the material could be spread by people walking around. Radioactive contamination may also be an inevitable result of certain processes, such as nuclear fuel reprocessing, which releases radioactive xenon. In cases where radioactive material cannot be contained, it may be diluted to safe concentrations.

There are a variety of techniques for containing radioactive materials to prevent them from becoming airborne and causing air pollution. For instance, liquids are stored in high-integrity tanks or containers with a sump system to detect leakage. When there is a risk of the material becoming airborne, a glovebox is often used, which is kept under slight negative pressure, and the vent gas is filtered through high-efficiency filters.

Nuclear power plants do not produce air pollution while operating, but the processes for mining and refining uranium ore and making reactor fuel require large amounts of energy. Additionally, the creation of radioactive wastes is a major environmental concern related to nuclear power. These wastes, such as uranium mill tailings and spent reactor fuel, can remain radioactive and dangerous to human health for thousands of years.

Industrial processes

Specific industrial sectors with high greenhouse gas emissions include cement manufacturing, metal production, refineries, pulp and paper mills, and chemical manufacturing. For example, the production of liquid natural gas and the operation of kilns, boilers, drying operations, and asphalt and cement production use landfill methane gas as fuel. Additionally, the burning of coal in power plants emits gases and particulate matter containing metals and organic compounds, including polycyclic aromatic hydrocarbons (PAHs). PAHs are also produced as a byproduct in various industrial processes, such as iron, steel, and rubber product manufacturing, as well as power generation.

Fluorinated gases, such as hydrofluorocarbons, are another type of emission produced by industries. These gases are often used as substitutes for chlorofluorocarbons (CFCs), which have been outlawed in many places due to their ozone-depleting properties. Furthermore, the heating of buildings, waste incineration, landfill disposal practices, and agricultural activities contribute to air pollution through the emission of various gases and particulate matter.

To mitigate industrial air pollution, several strategies can be employed, including industrial processes upgradation, energy efficiency improvements, agricultural waste burning control, and fuel conversion to lower-carbon alternatives. The implementation of process control and energy management systems can also help improve combustion efficiency and fuel use across industries.

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