Brian Barton
Air pollution is a pressing issue that affects the health and well-being of people worldwide, causing an estimated 6.7 million premature deaths annually. It arises from various sources, including mobile sources like vehicles, stationary sources like power plants and industrial facilities, area sources such as agricultural activities and cities, and natural sources like wildfires and volcanoes. These sources release pollutants into the atmosphere, including particulate matter (PM), ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and volatile organic compounds (VOCs). PM, a mixture of solid and liquid particles, can be directly emitted or formed in the atmosphere through chemical reactions. Ozone, while beneficial in the upper atmosphere, becomes harmful at ground level, contributing to smog formation and damaging vegetation. Carbon monoxide, an odourless and colourless gas, is produced through the incomplete combustion of fuels. Sulfur dioxide and nitrogen dioxide, also released from combustion processes, have adverse effects on human health and the environment. Addressing air pollution is crucial to protect public health, especially in low- and middle-income countries bearing the brunt of its impacts.
| Characteristics | Values |
|---|---|
| Number of premature deaths caused by air pollution annually | 6.7 million |
| Percentage of premature deaths caused by outdoor air pollution in 2019 | 68% ischaemic heart disease and stroke, 14% chronic obstructive pulmonary disease, 14% acute lower respiratory infections, 4% lung cancers |
| Percentage of premature deaths occurring in low- and middle-income countries | 89% |
| Region with the greatest number of premature deaths | WHO South-East Asia and Western Pacific Regions |
| Main sources of black carbon | Incomplete combustion of fossil fuels, biofuels and biomass |
| Natural sources of air pollution | Wind-blown dust, wildfires, volcanoes |
| Human-generated sources of air pollution | Cars, buses, planes, trucks, trains, power plants, oil refineries, industrial facilities, factories, agricultural areas, cities, wood-burning fireplaces |
| Pollutants included in the WHO global air quality guidelines | Particulate matter (PM), black carbon, ultrafine particles (UFP), polycyclic aromatic hydrocarbons (PAH), formaldehyde |
| Six common air pollutants ("criteria" air pollutants) | Particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, lead |
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Particulate matter (PM)
The sources of PM vary depending on the size of the particles. Coarse particles, or PM10, are primarily derived from natural sources such as pollen, sea spray, and wind-blown dust from erosion, agriculture, and natural disasters. They can also come from human activities like construction, unpaved roads, and mining operations. On the other hand, fine particles, or PM2.5, are more likely to be the result of combustion processes, such as the burning of fuels in power generation, industrial activities, and vehicle emissions. They can also form in the atmosphere through chemical reactions between gases, such as sulphur dioxide (SO2) and nitrogen oxides (NOx).
The health impacts of PM are significant. Due to their small size, fine particles (PM2.5) can penetrate deep into the lungs and even enter the bloodstream. Exposure to PM2.5 has been linked to adverse health effects, including respiratory and cardiovascular issues, aggravated asthma, decreased lung function, and an increased risk of premature death, especially in individuals with pre-existing heart or lung conditions. Long-term exposure to PM2.5 has also been associated with reduced lung function growth in children. While PM10 particles are larger and primarily affect the respiratory system, long-term exposure to these particles has been linked to respiratory mortality as well.
In addition to its health impacts, PM pollution can also influence climate change and ecosystems. Certain constituents of PM, such as black carbon, have warming effects on the atmosphere, while others like nitrate and sulphate have cooling effects. Deposition of PM on plants and water bodies can impact plant growth and water quality. Furthermore, PM can contribute to reduced visibility, often referred to as "haze," in many regions, including national parks and wilderness areas.
To protect public health and address the issues associated with PM pollution, regulatory bodies like the US Environmental Protection Agency (EPA) have established standards and implemented measures to reduce emissions of particulate matter and its precursor pollutants. The EPA's National Ambient Air Quality Standards (NAAQS) include PM as one of the criteria air pollutants, and the agency works with state, tribal, and local agencies to improve air quality across the country. Additionally, tools like the Air Quality Index (AQI) help individuals stay informed about the air quality in their areas and take appropriate actions to protect their health when necessary.
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Mobile sources
Motor vehicles emit various pollutants, including carbon monoxide, carbon dioxide, nitrogen oxides, and particulate matter. Carbon monoxide forms when carbon in fuel does not burn completely, and it reduces oxygen delivery to the body's organs and tissues, posing a significant risk to those with heart and respiratory diseases. Carbon dioxide is a prominent greenhouse gas, contributing to climate change. Nitrogen oxides form when fuel burns at high temperatures in motor vehicle engines, and they contribute to the formation of ozone and smog.
Particulate matter, or particle pollution, refers to a mixture of solid particles and liquid droplets found in the air. These particles can be emitted directly from sources such as construction sites, unpaved roads, and fires, or they can form in the atmosphere through chemical reactions involving pollutants like sulfur dioxides and nitrogen oxides emitted from vehicles and industrial sources. People living or working near major roads are at an increased risk of experiencing health problems associated with air pollution exposures, including respiratory issues, coughing, and difficulty breathing.
To address mobile source pollution, environmental regulatory agencies like the U.S. Environmental Protection Agency have established policies and regulations to minimize air pollution from these sources. This includes implementing design and fuel standards, such as corporate average fuel economy standards and laws banning leaded gasoline in the United States. However, the increasing number of motor vehicles on the road presents challenges in achieving desired emissions goals.
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Stationary sources
Power Plants
Power generation facilities, particularly those that burn fossil fuels, are significant contributors to air pollution. The combustion of fuels, such as coal, oil, and natural gas, releases various pollutants, including particulate matter (PM), nitrogen oxides (NOx), sulfur dioxide (SO2), and carbon monoxide (CO). These emissions can lead to reduced air quality, acid rain, and the formation of ground-level ozone, a major component of smog. Power plants are a major source of criteria air pollutants, which are regulated by the Clean Air Act in the United States.
Industrial Facilities
Factories and industrial processes emit a wide range of pollutants. For example, the combustion of fuels in industrial boilers can release NOx and SO2, while certain industrial activities, such as oil and gas development, contribute to elevated ozone concentrations. Additionally, industrial facilities may release particulate matter, volatile organic compounds (VOCs), heavy metals, and toxic chemicals, depending on the specific industrial processes involved.
Refineries and Petrochemical Plants
Oil refineries and petrochemical plants are responsible for emissions of various pollutants, including VOCs, NOx, SO2, and particulate matter. The refining of crude oil and the processing of petroleum products can result in the release of these pollutants, which contribute to air quality issues and have potential health impacts on nearby communities.
Boilers and Heating Systems
Boilers used for industrial processes or space heating, particularly those that burn fossil fuels, can emit pollutants such as NOx, SO2, and CO. Inefficient or improperly maintained boilers may produce higher levels of emissions, especially in older systems or those without proper emission control technologies.
Area Sources
While less significant individually, multiple smaller pollution sources grouped together can create area sources of pollution. This can include pollution from residential areas, commercial establishments, or agricultural practices. For example, the collective emissions from vehicles, heating systems, and cooking in a densely populated urban area can contribute to local air quality issues.
It is important to note that the impact of stationary sources of pollution can vary depending on factors such as the type and quantity of emissions, the presence of emission control technologies, and the surrounding environmental conditions, including wind patterns and proximity to populated areas. Regulations and standards, such as the Clean Air Act in the United States, aim to control and reduce emissions from these stationary sources to mitigate their impact on atmospheric pollution.
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Natural sources
Wildfires
Wildfires are one of the largest sources of black carbon, or soot, which is very harmful to human health and the environment. Black carbon can lead to lung and heart diseases 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 air 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 gases into the atmosphere, including hydrogen sulfide, radon, sulfuric acid, hydrogen, carbon monoxide, hydrogen chloride, hydrogen fluoride, helium, and carbon dioxide (CO2). Carbon dioxide is a greenhouse gas that contributes to global warming. Volcanoes release significant amounts of CO2 into the atmosphere both through eruptions and underground magma. Volcanic gases can be odorless, invisible, and very dangerous, and even lethal when inhaled at high concentrations. However, local authorities usually have monitoring systems in place to alert people living in at-risk areas.
Sandstorms
Sandstorms can emit particulate matter, nitrogen oxides, and volatile organic compounds, which sometimes affect human health and the climate.
Vegetation
Plants emit volatile organic compounds and organic compounds that contribute to air pollution. Livestock, such as cows and sheep, also release large amounts of methane through belching and flatulence. Methane is a colourless gas produced in their stomachs when bacteria break down the food they eat. Livestock is the biggest source of methane globally, and it is the second most important greenhouse gas, capable of causing climate change.
Sea Spray
Sea spray can contain coarse particles, including sea salt, that are considered air pollutants.
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Black carbon
Simple technologies and improved household energy solutions can also play a significant role in reducing indoor air pollution and black carbon emissions. For example, switching from solid fuels and kerosene to cleaner alternatives for cooking, lighting, and heating can reduce exposure to black carbon and improve health, especially in households that rely on crude fuels. Additionally, the use of clean cookstoves can reduce black carbon emissions and improve the well-being of women and children, who are often responsible for cooking and are more vulnerable to the health impacts of indoor air pollution.
Overall, black carbon is a significant atmospheric pollutant that contributes to both climate change and adverse health effects. However, targeted strategies to reduce black carbon emissions can provide relatively rapid climate and health benefits, making it a promising target for mitigation efforts in the near term.
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Frequently asked questions
The main sources of outdoor air pollution are mobile sources such as cars, buses, planes, trucks, and trains; stationary sources such as power plants, oil refineries, industrial facilities, and factories; area sources such as agricultural areas, cities, and wood-burning fireplaces; and natural sources such as wind-blown dust, wildfires, and volcanoes.
Air pollution is responsible for an estimated 6.8 million premature deaths annually, with 68% due to ischemic heart disease and stroke, 14% due to chronic obstructive pulmonary disease, 14% due to acute lower respiratory infections, and 4% due to lung cancer. Long-term exposure to polycyclic aromatic hydrocarbons (PAH) has also been linked to lung cancer.
PM2.5 refers to fine inhalable particles with diameters of 2.5 micrometres or smaller. It is generated by combustion processes such as motor vehicles, power plants, wood burning, certain industrial processes, and fires. PM2.5 can remain suspended in the air for weeks and have negative health effects, especially for individuals with heart or lung disease.
Ground-level ozone is an air pollutant that is harmful to breathe and damages crops, trees, and other vegetation. It is a major constituent of smog and is formed through the reaction of gases in the presence of sunlight. In contrast, the ozone layer in the stratosphere (approximately six to ten miles above the Earth's surface) protects life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun.
Household air pollution, such as that caused by cooking and heating with polluting fuels, contributes to ambient air quality. It can lead to indoor air pollution and also be transported outdoors, affecting the overall air quality in a region.
