Airborne Pollutants: Their Fate And Impact

Air pollution is a pressing issue that poses significant risks to human health and the planet. It refers to the release of pollutants into the air, which can be in the form of gases, solid particles, or liquid droplets. These pollutants contaminate the indoor or outdoor environment, modifying the natural characteristics of the atmosphere. The sources of air pollution are diverse and context-specific, but human activities, such as burning fossil fuels, industrial processes, and vehicle emissions, are major contributors. Once released into the air, pollutants can spread and have detrimental effects on human health, the environment, and even infrastructure.

So, what exactly happens to these pollutants once they are in the air?

The formation of particulate matter

Particulate matter is a term used to describe the secondary smaller particles that are formed when pollutants break down. These particles are typically microscopic particles of solid or liquid matter suspended in the air. The smaller the particulate matter, the worse it is for human health, as it can enter our lungs and airways and, in some cases, the bloodstream. Particulate matter less than 10 micrometres in diameter can get deep into the lungs, and is linked to a 13% increased risk of heart attacks. Even smaller particles, less than or equal to 2.5 micrometres in diameter, can penetrate deeper into the lungs and are associated with premature death. These smaller particles are also known as "fine particles" and are found in smoke and haze. Larger particles, between 2.5 and 10 micrometres in diameter, are known as "coarse particles" and are found in wind-blown dust.

Particulate matter can be formed from a variety of sources, including natural and anthropogenic processes. Natural sources include windblown dust, while human activities such as burning fossil fuels, aircraft, construction, and biomass burning also generate significant amounts of particulate matter. The composition of particulate matter typically includes sulfur dioxide, nitrogen oxides, carbon monoxide, mineral dust, and organic matter. These particles are hygroscopic, meaning they can absorb water, and when present in high humidity and low temperatures, sulfur dioxide is converted to sulfate, leading to reduced visibility and a red-orange-yellow haze.

The health effects of particulate matter exposure are significant, with worldwide exposure linked to millions of deaths from heart disease, stroke, lung cancer, chronic lung disease, and respiratory infections. It is considered the most harmful form of air pollution, as it can penetrate deep into the lungs and brain from bloodstreams. Even without direct exposure, particulate matter can adversely affect human health by impacting disease-causing bacteria. It also has effects on climate and precipitation.

To reduce the health risks associated with particulate matter, interventions and initiatives are necessary to promote sustainable land use, cleaner energy and transport, energy-efficient housing, improved waste management, and better urban development. These measures can help reduce the sources of ambient air pollution and protect public health.

Direct exposure to toxic gases

Toxic air pollutants, also known as hazardous air pollutants, are substances that are known or suspected to cause cancer, birth defects, and other serious health issues. They can be gases such as hydrogen chloride, benzene, and toluene, or compounds and metals such as asbestos, cadmium, mercury, and chromium. The U.S. Environmental Protection Agency has identified 188 pollutants as hazardous.

Major sources of outdoor toxic air pollutants include emissions from coal-fired power plants, industries, refineries, vehicles, trucks, and buses. Certain industries are also associated with specific toxic air pollutants. For example, ethylene oxide leaks from medical equipment sterilization facilities and other industrial sources. Chemical releases, such as accidents during the transportation of hazardous materials, can also result in the release of toxic gases into the air.

Indoor air can also contain hazardous pollutants, including tobacco smoke, asbestos from building materials, and consumer products like cleaning supplies and air fresheners. These indoor sources of pollution are of particular concern as they can directly impact the health of those who reside in the affected spaces.

The effects of direct exposure to toxic gases can vary depending on the specific gas and the individual's health. For example, exposure to lead, even in minimal amounts, can impact children's IQ and ability to learn, while larger amounts can damage their brains and kidneys. Polycyclic aromatic hydrocarbons (PAHs), which are by-products of traffic exhaust and wildfire smoke, have been linked to eye and lung irritation, blood and liver issues, and cancer.

Climate change intensifies air pollutants

Air pollution is defined as the contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. It is a pressing environmental and public health issue, causing approximately 7 million premature deaths annually. Climate change intensifies air pollutants and poses a significant threat to air quality, with a range of harmful consequences.

Firstly, climate change exacerbates the presence of specific air pollutants, such as ground-level ozone and particulate matter. Ground-level ozone, or smog, forms when emissions from burning fossil fuels interact with sunlight. Warmer temperatures associated with climate change increase the occurrence of ground-level ozone, particularly during hot and sunny days. This ground-level ozone acts as a greenhouse gas, trapping heat in the atmosphere and further contributing to climate change. Particulate matter, which includes soot, is composed of tiny particles of chemicals, soil, smoke, dust, or allergens. Climate change-related factors, such as droughts and wildfires, contribute to increased particulate matter in the air. For example, dust from droughts and smoke from wildfires can significantly reduce air quality and have detrimental health effects.

Secondly, climate change leads to an increase in allergenic air pollutants, including mold and pollen. Extreme weather events and increased flooding caused by climate change create damp conditions that foster mold growth. Mold exposure can trigger allergic reactions and asthma attacks and produce toxic effects when inhaled. Rising temperatures and higher carbon dioxide levels associated with climate change lengthen the pollen season and stimulate plants to produce more pollen. This intensification of pollen allergies poses additional health risks, particularly for individuals with respiratory conditions.

Moreover, climate change impacts indoor air quality, which is closely linked to outdoor air pollution. Increases in outdoor air pollutants, such as ozone and particulate matter, can result in higher indoor exposures. Climate change-related precipitation and storms can also lead to damp indoor environments, promoting the growth of mold, dust mites, bacteria, and other indoor pollutants. These indoor air pollutants have been linked to serious health issues, including respiratory diseases, asthma, and cancer.

The effects of climate change on air quality vary regionally, with certain areas experiencing more severe consequences. For instance, the U.S. Southwest faced a severe long-term drought in 2021, contributing to increased particulate matter and air quality issues. Additionally, regulatory initiatives, partnership programs, and individual actions can play a crucial role in mitigating the impacts of climate change on air quality. By reducing air pollutants and greenhouse gas emissions, we can address both air quality degradation and the drivers of climate change.

Natural sources of air pollution

While most harmful air pollution is caused by human activity, natural sources of air pollution are varied and include wildfires, sandstorms, sea spray, volcanoes, vegetation, decomposition, lightning, and radon gas. These natural sources release pollutants that affect air quality and can pose health risks and contribute to climate change.

Wildfires

Wildfires are one of the largest sources of black carbon, which is very harmful to human health and the environment. Black carbon, or soot, can lead to lung and heart disease and premature death. It reduces sunlight, impacts plant ecosystems, and absorbs solar heat, contributing to global warming at a rate up to 1,500 times greater than that of CO2. Wildfire pollutants can cause a range of adverse health effects, including difficulty breathing, an increased risk of asthma, heart failure, and premature death. While wildfires can be a natural phenomenon, human-driven global warming has exacerbated their frequency and intensity.

Volcanoes

Volcanoes emit massive amounts of sulphur dioxide, hydrogen sulfide, radon, sulfuric acid, hydrogen, carbon monoxide, hydrogen chloride, hydrogen fluoride, and helium into the atmosphere. These emissions can increase background pollution levels for years, even in areas far from the original source.

Livestock

Animals like cows and sheep release large amounts of methane through belching and flatulence. Methane is a colourless gas produced in their stomachs when bacteria break down their food. Livestock is the biggest source of methane worldwide, and it is the second most important greenhouse gas, which can cause climate change.

Vegetation and Organic Compounds

Organic compounds from plants, sea salt, suspended soils, and dust (e.g. from the Sahara) can contribute to air pollution. In dry regions like deserts, high winds can lift sand and dust particles, causing storms of particulate matter. These particles can be harmful when inhaled and can have adverse health effects, especially for those with respiratory issues.

Other Natural Sources

Other natural sources of air pollution include sandstorms, sea spray, decomposition, lightning, and radon gas. Additionally, natural processes such as mining, smelting, and foundry activities can emit various metals and particulate matter into the air, contributing to air pollution. Other natural sources of pollution include agricultural practices that release ammonia gas and pesticides, which contain toxic volatile organic compounds.

How air pollution affects human health

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is a major threat to global health and prosperity, causing millions of deaths each year. According to the World Health Organization (WHO), indoor and outdoor air pollution is responsible for nearly seven million deaths worldwide annually.

There are three key pathways by which pollutants can cause harm: direct exposure, formation of particulate matter, and chronic exposure. Direct exposure to toxic gases can have acute effects on health, especially for people with existing respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD). Fine particulate matter (PM 2.5) can be inhaled deeply into the lungs and contribute to serious health problems. These particles can also enter the bloodstream and cause or worsen breathing and lung diseases, leading to hospitalizations, cancer, or even premature death.

Both short-term and long-term exposure to air pollution can lead to a wide range of diseases, including respiratory infections, stroke, chronic obstructive pulmonary disease, lung cancer, and aggravated asthma. Children, adolescents, and older people are particularly vulnerable to the health impacts of air pollution, as their bodies and immune systems are still developing or weakening with age. Low-income communities and minority populations are also disproportionately affected by air pollution and are more vulnerable to adverse health outcomes.

The sources of air pollution are multiple and context-specific. Outdoor pollution comes from vehicles, power generation, industry, and residential energy use for cooking and heating. Natural sources include wildfires, volcanic eruptions, and gases emitted from decomposing organic matter in soils. Household combustion devices, motor vehicles, industrial facilities, and forest fires are common sources of human-made air pollution.

To mitigate the health risks associated with air pollution, policies and interventions that support sustainable land use, cleaner energy and transport, energy-efficient housing, and better waste management can effectively reduce key sources of ambient air pollution. The World Health Organization (WHO) and other organizations provide guidance and initiatives to address the health risks of air pollution and improve air quality.

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