Anthropogenic Air Pollution: What's Not Caused By Humans?

While most air pollution is caused by human activity, there are several natural processes and sources that contribute to air pollution. These include volcanic eruptions, dust storms, smoke and ash from wildfires, and biological decay. Natural sources of air pollution can have long-term effects on ecosystems, and it is important to monitor how natural air pollution is changing over time. While anthropogenic air pollution refers to the contamination of the atmosphere caused by human activities, primarily through the burning of fossil fuels and industrial processes, natural sources of air pollution are not caused by human activities and are instead the result of natural processes.

Volcanic eruptions

Sulphur dioxide (SO2) is a major pollutant released during volcanic eruptions. SO2 is a toxic gas that can irritate the nose, throat, and eyes, even at low concentrations. In 1980, the eruption of Mount St. Helens released up to 3750 tons of SO2 per day, causing an international pollution event. The gas formed a cloud that migrated across the United States in three days and reached around the world in 15 days.

Another significant pollutant emitted during volcanic eruptions is carbon dioxide (CO2). Due to its light weight, CO2 is easily expelled and dispersed during an eruption. However, because it is heavier than air, it tends to remain close to the Earth's surface. High concentrations of CO2 can be harmful to humans and other animal species, potentially leading to unconsciousness and death.

Volcanic ash is another byproduct of eruptions that can contribute to air pollution. The extent of the ash cloud's dispersion depends on factors such as particulate size, wind speed, and direction. Ash clouds can travel great distances and affect areas far from the eruption site. Volcanic ash can irritate the airways and cause respiratory issues, especially when mixed with other volcanic gases.

While volcanic eruptions are not anthropogenic sources of air pollution, they can have far-reaching consequences for the atmosphere and human populations. The release of gases and particles during eruptions can lead to short-term and long-term environmental and health impacts, underscoring the importance of monitoring and preparedness for volcanic activity.

Wildfires

While most air pollution is caused by human activity, there are some natural sources of air pollution. One of these is wildfires, which release a range of pollutants into the atmosphere, including black carbon, carbon monoxide, nitrogen oxides, and particulate matter. These pollutants can have severe impacts on human health and the environment, and they can also contribute to climate change.

Climate change plays a significant role in the rising frequency and intensity of wildfires. Increased drought conditions, higher temperatures, and stronger winds create an environment that is more susceptible to fires. Wildfires, in turn, release large amounts of carbon and other greenhouse gases, exacerbating climate change. This positive feedback loop between wildfires and climate change creates a vicious cycle that is challenging to break.

The impact of wildfires extends beyond their immediate physical reach. The smoke and pollutants released into the atmosphere can travel long distances, affecting areas far from the source of the fires. Fine particulate matter (PM2.5), for example, can have severe health impacts, including aggravating asthma, triggering lung disease, causing heart attacks, and leading to premature deaths. The health risks associated with wildfire smoke are of great concern, and policymakers are urged to address these super pollutants through interventions with long-term, sustainable impacts.

To break the cycle of wildfires and reduce their impact, a shift from a reactive to a proactive approach is necessary. This includes increasing investment in planning, prevention, and preparedness, as advocated by the 'Fire Ready Formula'. Additionally, initiatives such as the UN Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation (UN-REDD) and the 'REDD+' framework under the Paris Agreement aim to protect forests and reduce emissions from deforestation and forest degradation.

Wind-blown dust

Natural sources of air pollution include sulphur and chlorine gases from volcanic activity, smoke and ash from wildfires, dust storms, and biological decay. While dust storms are a natural source of air pollution, wind-blown dust can also be a result of human activity.

The impact of wind-blown dust on air quality can vary depending on factors such as wind speed, the amount of dust available, and local terrain conditions. In some regions, such as the western United States, it can be particularly challenging to simulate dust concentrations and predict the impact of wind-blown dust on regional air quality.

To assess the impact of wind-blown dust on air quality, scientists use models such as the Unified Regional Air Quality Modeling System (AURAMS) and its chemical transport model (CTM). These models take into account meteorology, regional configurations, and the distribution of soil dust aerosol to quantitatively evaluate the influence of wind-blown soil dust on a regional level.

Radon gas

Radon is a naturally occurring, radioactive gas that is produced from the natural radioactive decay of uranium, which is found in all rocks and soils. Radon is invisible, odourless, and tasteless. It can be found in water and air, and can even seep into buildings through cracks in the foundation, basement, or crawl space, or through drains, pipes, and construction gaps.

Radon is known to be harmful to human health, particularly respiratory health. When radon is inhaled, radioactive particles are deposited on the cells lining the airways, potentially causing damage to DNA and increasing the risk of lung cancer. The risk is heightened in buildings with poor ventilation, such as homes, schools, and offices, where radon can accumulate and reach dangerous concentrations. The highest levels of indoor radon are typically found in mines, caves, and water treatment facilities.

The concentration of radon in buildings depends on various factors, including local geology, the underlying rock and soil composition, the building's construction, ventilation, and air-tightness. Radon can also dissolve and accumulate in groundwater sources, such as water pumps or drilled wells in uranium-rich geological areas. While epidemiological studies have not confirmed a link between consuming radon-containing water and an increased risk of stomach cancer, inhaling radon released from water during activities like showering or laundry can pose a risk to lung health.

The World Health Organization (WHO) has published guidelines for radon in drinking water and indoor air quality. The EPA recommends taking action to reduce indoor radon levels if they reach or exceed 4.0 picocuries per liter (pCi/L) of air, which is the standard unit of measurement for radon gas. To reduce indoor radon levels, corrective actions such as radon mitigation systems, improved ventilation, and sealing of cracks and gaps can be implemented.

In summary, radon gas is a naturally occurring radioactive gas that can negatively impact indoor air quality and pose risks to human health, particularly respiratory health. It is invisible, odourless, and tasteless, making it difficult to detect without testing. High concentrations of radon, especially in enclosed spaces with poor ventilation, increase the risk of lung cancer. To mitigate these risks, it is important to test for radon and implement corrective actions to reduce indoor radon levels.

Indoor smoking

Smoking indoors is a significant contributor to indoor air pollution. Environmental tobacco smoke (ETS), also known as secondhand smoke, is a mixture of exhaled mainstream smoke and sidestream smoke released from smouldering tobacco products. Tobacco smoke contains around 5000 individual compounds, including toxic substances and carcinogens. These toxic and carcinogenic substances are also present in ETS, which is responsible for substantial levels of indoor particulate air pollution.

Particulate matter (PM) is one of the harmful components of ETS. PM is composed of a large variety of chemicals, including primary pollutants like nitric oxide and volatile organic compounds (VOCs) that come directly from smokestacks, construction sites, and fires. When released indoors, these pollutants can accumulate and result in high concentrations of indoor air pollution.

The adverse health effects of ETS are well-documented. Exposure to ETS has been linked to illness and premature death, making it a substantial public health threat. The toxicological substances in ETS can deeply penetrate the airways and deposit harmful particulate matter. This is particularly concerning in industrialized countries, where people spend a significant amount of time indoors, up to 90% according to estimates.

To mitigate the impact of ETS on indoor air quality, comprehensive smokefree policies for tobacco smoke products have been proposed and researched extensively. These policies recommend prohibiting smoking indoors, including in cars, vehicles, and near entryways to enclosed spaces. While ventilation, filtration, and air cleaning techniques can reduce exposures, the only way to eliminate secondhand exposure is through strict adherence to smokefree policies.

It is important to note that indoor smoking not only affects the smoker but also those around them. By smoking indoors, individuals expose their loved ones, neighbours, and others nearby to harmful chemicals and the risks associated with secondhand smoke. Therefore, it is strongly advised to smoke outdoors and away from enclosed spaces to protect the health and well-being of oneself and others.

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