Meghan Hodges
Natural pollutants are substances that are released into the environment by non-human sources. They can affect air quality and contribute to climate change, with potential risks to human health. Examples of natural sources of pollution include wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, radon gas, and microbial activity. While most harmful air pollution is caused by human activity, natural sources also play a significant role in emitting pollutants such as particulate matter, ozone, methane, and volatile organic compounds. These natural pollutants can have both localised and global impacts, underscoring the importance of monitoring and understanding their effects to mitigate potential risks.
| Characteristics | Values |
|---|---|
| Natural sources | Wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, radon gas, forest fires, microbial activity |
| Particulate matter | Solid or liquid compounds suspended in the air |
| Categories | PM2.5, PM10 |
| PM2.5 diameter | 2.5 micrometers or smaller |
| PM10 diameter | 10 micrometers or smaller |
| Composition | Varies based on location |
| Atmospheric deposition | Processes that remove gases and particulates from the atmosphere and incorporate them into ecosystems |
| Forms | Deposition of gases, dry deposition of particulates, wet deposition through precipitation |
| Pollutants | Ozone, methane, volatile organic compounds, black carbon, radon, sulfuric acid, hydrogen, carbon monoxide, hydrogen chloride, hydrogen fluoride, helium, nitrogen dioxide, sulfur dioxide, lead, polycyclic aromatic hydrocarbons, elemental mercury |
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What You'll Learn
Wildfires, a source of black carbon (soot)
Natural pollutants are emissions that affect air quality and are released from natural sources such as wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, and radon gas. While most harmful air pollution is caused by human activity, natural sources also contribute to the problem.
Wildfires are one of the largest sources of black carbon, also known as soot. Wildfires inject large amounts of black carbon particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. These particles can remain in the stratosphere for a long time, absorbing solar heat and contributing to global warming at a rate up to 1,500 times greater than that of CO2.
The impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere has been studied by researchers like JL Crockett, AL Westerling, and Rajan Chakrabarty. Crockett and Westerling found that temperature and precipitation extremes intensify Western US droughts, wildfire severity, and tree mortality in the Sierra Nevada. Chakrabarty, as part of a multi-institutional field campaign called FIREX-AQ, mapped fresh smoke plumes and tracked their spread.
Black carbon particles from wildfire smoke can acquire an additional layer of organic matter, which increases their heat absorption capacity. This has important implications for understanding the Earth's future climate, as current climate models may underpredict warming if they do not account for this coating.
Wildfires emit fine particle pollution, including black carbon, which can lead to a range of adverse health effects such as difficulty breathing, an increased risk of asthma, heart failure, and premature death. Wildfires also affect the climate by releasing carbon dioxide and other greenhouse gases, as well as damaging forests that would otherwise remove CO2 from the air. While renewed forest growth can offset some of the CO2 emissions, human activities are resulting in bigger and more intense fires, making their emissions a significant contributor to global warming.
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Volcanic gases, including hydrogen sulfide and carbon dioxide
Volcanic gases are gases released by active or dormant volcanoes. They include gases trapped in cavities in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, volcanic craters, or vents. They can also be emitted through groundwater heated by volcanic action.
Volcanic gases include water vapour, carbon dioxide, sulphur (as sulphur dioxide), hydrogen sulfide, nitrogen, argon, helium, neon, methane, carbon monoxide, and hydrogen. Other compounds detected in volcanic gases include hydrogen chloride, hydrogen fluoride, hydrogen bromide, and oxygen.
Carbon dioxide (CO2) is a greenhouse gas that contributes to global warming. Volcanoes release significant amounts of CO2 into the atmosphere through eruptions and underground magma. CO2 can collect in low-lying volcanic areas, posing lethal risks to humans and animals. Breathing air with more than 3% CO2 can lead to headaches, dizziness, increased heart rate, and difficulty breathing. At mixing ratios exceeding 15%, carbon dioxide quickly causes unconsciousness and death.
Hydrogen sulfide is a colourless, flammable gas with a strong, offensive odour. Hydrogen sulfide has been responsible for several deaths, including a volcanological observer at Papandayan in 1924, likely due to suffocation.
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Vegetation, which emits volatile organic compounds
Natural sources of air pollution include wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, and radon gas. Vegetation emits volatile organic compounds (VOCs) that contribute to air pollution. VOCs are signalling chemicals, similar to human pheromones, and are emitted by all plants. VOCs play a crucial role in plant interactions with biotic and abiotic factors, and they vary widely across species. They are involved in a wide class of ecological functions, including plant communication and defence mechanisms.
VOCs are emitted from leaf surfaces and are highly unstable due to their low boiling points, which cause the molecules to easily evaporate into the air. The smell of freshly cut grass, for example, is caused by a VOC. Conifer trees emit a flammable group of VOCs called terpenes, which are also emitted by pine forests. Terpenes are a class of VOCs that include isoprene, which is a significant contributor to the carbon in the atmosphere.
The emission of VOCs by plants can be influenced by various factors, including the species composition of neighbouring plants, insect herbivore feeding, and abiotic stress. For instance, red clover (Trifolium pratense) plants grown in communities containing the grass species Dactylis glomerata emitted higher amounts of monoterpenes and green leaf volatiles, resulting in overall higher VOC emissions. On the other hand, when grown with Geranium pratense, the emission of the homoterpene DMNT was significantly lower.
Additionally, VOC emissions can be induced by wounding or fluctuations of light and temperature. For example, homoterpenes were only emitted by plants subjected to herbivory by caterpillars. The measurement of VOCs can be challenging, but techniques such as chemical ionization mass spectrometry can help determine the amount and type of VOCs emitted by plants in real time.
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Sandstorms, which lift sand and dust particles into the air
Natural pollutants are emissions that affect air quality and are released from natural sources. Examples include particulate matter, ozone, methane, volatile organic compounds, and more. While most harmful air pollution is caused by human activity, natural sources such as wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, and radon gas also contribute to air pollution.
Sandstorms, also known as dust storms, are a type of natural pollutant that lifts sand and dust particles into the air. They are a meteorological phenomenon common in arid and semi-arid regions, such as deserts. Sandstorms occur when strong winds blow loose sand and dirt from dry surfaces. The fine particles are transported by saltation and suspension, moving from one place to another.
Saltation is the process by which sand particles are loosened and lifted into the air. As wind passes over loosely held particles, they start to vibrate and move across the surface. Repeatedly striking the ground, they break off smaller particles of dust that then become suspended in the air. This process induces a static electric field by friction, causing more sand particles to be lifted.
Sandstorms can have significant impacts on the environment and human health. They can reduce visibility, affecting transportation and posing risks to drivers. Intense sandstorms can force the closure of roads and airports, disrupt infrastructure, and impact energy production. Additionally, sandstorms can affect agriculture and livestock, reducing productivity and contributing to desertification over time.
The Sahara Desert is a key source of sandstorms, with dust being transported across the Mediterranean and as far as central Europe and Great Britain. Other regions affected by sandstorms include North Africa, the Middle East, Central Asia, China, and the United States. The frequency and intensity of sandstorms have been increasing due to factors such as poor land management, drought, and climate change.
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Radon gas, released from natural sources like rocks and soil
Radon is a colourless, odourless, and tasteless radioactive gas that is released from rocks and soil. It is a product of the natural radioactive decay of uranium, which is found in all rocks and soils. Radon gas escapes from the ground into the air, where it decays and produces further radioactive particles. These particles can be harmful when inhaled, as they deposit on the cells lining the airways, potentially causing lung cancer.
While radon gas is a natural pollutant, it is important to note that it primarily poses a health risk when concentrated in enclosed spaces, such as buildings. Radon concentrations tend to be higher indoors, especially in areas with minimal ventilation, and can vary significantly between adjacent buildings and within the same building over time. The greatest exposure to radon typically occurs in residential settings and indoor workplaces, where people spend a significant amount of time.
The concentration of radon in buildings depends on several factors, including local geology, the underlying rock and soil composition, construction techniques, ventilation, and domestic habits. Radon can enter buildings through various pathways, such as cracks in the floor, gaps around pipes or cables, windows, and drains. It is essential to monitor and mitigate high radon concentrations, especially in workplaces, to protect the health and safety of occupants.
Radon levels can be particularly high in certain types of workplaces, such as water treatment facilities, spa facilities using natural water, and mines. In these cases, employers are responsible for undertaking remedial or corrective actions if radon concentrations exceed established workplace norms. National authorities may also need to be notified and special regulatory requirements may apply.
The health risks associated with radon exposure have been well-studied. Radon is a major cause of lung cancer, with studies confirming that even low concentrations found in residential settings contribute to lung cancer cases worldwide. The risk of lung cancer increases proportionally with increasing radon exposure, and it is even more significant for individuals who smoke.
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Frequently asked questions
Natural pollutants are emissions that affect air quality and are released from natural sources such as wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, and radon gas.
Natural pollutants can pose health risks and contribute to climate change. For example, wildfires are a large source of black carbon, which can lead to lung and heart diseases and premature death. They also reduce sunlight, impact plant ecosystems, and absorb solar heat, contributing to global warming at a rate up to 1,500 times greater than that of CO2.
Natural sources emit particulate matter, which refers to solid or liquid compounds suspended in the air. Particulate matter can be hazardous, as it can enter our bloodstream, travel deep into our lungs, and cause respiratory and cardiovascular damage.
