Bronte Wells
Air pollution is a major threat to global health and prosperity, causing around 7 or 8 million deaths each year. It consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. These pollutants can take the form of gases, solid particles, or liquid droplets, and they are released into the atmosphere at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. The most common sources of air pollution include the burning of fossil fuels, vehicle emissions, industrial processes, waste management, and agriculture. Some specific examples of pollutants include ozone, nitrogen oxides, carbon monoxide, volatile organic compounds, polycyclic aromatic hydrocarbons, and particulate matter.
| Characteristics | Values |
|---|---|
| Particulate matter | Fine particulate matter (PM 2.5) is 30 times thinner than a human hair and can be inhaled deeply into lung tissue. |
| Carbon monoxide | Pollutants emitted by cars, power plants, industrial boilers, and refineries. |
| Ozone | Ground-level ozone is created when sunlight reacts with certain chemicals from sources of burning fossil fuels. |
| Nitrogen oxides | Components of motor vehicle emissions and byproducts of industrial processes. |
| Sulfur oxides | Byproducts of industrial processes. |
| Volatile organic compounds | Vaporize at or near room temperature and are released by paints, cleaning supplies, pesticides, etc. |
| Polycyclic aromatic hydrocarbons | By-products of traffic exhaust and wildfire smoke. |
| Greenhouse gases | Include carbon dioxide, methane, and ozone. |
| Allergens | Include mold and pollen. |
| Wildfire smoke | Can contain particulate matter, polycyclic aromatic hydrocarbons, and other pollutants. |
| Secondhand smoke | Can increase the risk of lung cancer. |
| Hazardous chemicals | Include dioxins, mercury, and lead. |
| Gases and particles | Include carbon dioxide, carbon monoxide, nitrogen oxides, sulfur oxides, volatile organic compounds, polycyclic aromatic hydrocarbons, and fine particulate matter. |
| Solid and liquid particles | Include aerosols, dust, and pollen. |
| Certain gases | Include ozone and volatile organic compounds. |
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What You'll Learn
- Particulate matter, including soot and other fine particles
- Gaseous pollutants, such as ozone, nitrogen oxides, and carbon monoxide
- Volatile organic compounds, which vaporize at room temperature
- Polycyclic aromatic hydrocarbons, organic compounds containing carbon and hydrogen
- Natural sources, like wildfires, dust storms, and volcanic eruptions
Particulate matter, including soot and other fine particles
Particulate matter, also known as particle pollution, refers to a mix of solid and liquid particles that vary in size and are suspended in the air we breathe. These particles are often so small that they can only be detected using an electron microscope. Particulate matter is composed of chemicals such as sulfates, nitrates, carbon, mineral dust, elemental black carbon (soot), volatile organic carbon compounds, heavy metals, and ammonia.
Sources of particulate matter include vehicle and industrial emissions from fossil fuel combustion, cigarette smoke, and the burning of organic matter such as wildfires. Human activities and natural sources emit gases that react with other gases in the atmosphere to form particles. For example, nitrogen dioxide and sulfur dioxide pollutants can react with oxygen and water vapour in the air to form nitrate and sulfate particles.
The combustion of carbon-based fuels, such as burning wood in residential fireplaces and wood stoves, as well as wildfires, agricultural fires, and prescribed fires, are some of the largest sources of particulate matter. Fine particles, known as PM2.5, with diameters of 2.5 micrometres or smaller, pose the greatest risk to human health. These fine particles can be inhaled deeply into lung tissue and have been linked to serious health issues, including respiratory and cardiovascular diseases, lung disease, decreased lung function, asthma attacks, and certain cardiovascular problems such as heart attacks and irregular heartbeats.
Health studies have shown a significant association between exposure to fine particles and premature death. The effects of particulate matter on health can vary depending on individual health risks and the cumulative impacts of multiple pollutants. Children, older adults, and people with heart and lung disease are particularly sensitive to fine particle exposure.
While air quality has improved in recent decades due to stricter standards and regulations, such as the Clean Air Act, it is important to continue monitoring and reducing emissions to protect public health and improve air quality.
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Gaseous pollutants, such as ozone, nitrogen oxides, and carbon monoxide
Gaseous air pollutants such as ozone, nitrogen oxides, and carbon monoxide are detrimental to human health and the planet. According to the World Health Organization (WHO), air pollution, including these gaseous pollutants, is responsible for nearly seven million deaths globally each year. Ninety-nine per cent of people currently breathe air that exceeds the WHO's guideline limits for pollutants, with those in low- and middle-income countries suffering the highest exposures.
Ozone (O3), often referred to as smog, is an atmospheric gas formed at ground level when pollutants from cars, power plants, industrial boilers, refineries, and other sources chemically react in the presence of sunlight. Ozone is a major public health concern, and exposure to high levels of ground-level ozone can lead to respiratory issues, particularly in children, who are more susceptible to developing asthma in high-ozone communities.
Nitrogen oxides (NOx) are produced during combustion processes, from nitrogen compounds in fuel, and by the direct combination of atmospheric oxygen and nitrogen in flames. They are also formed naturally by lightning and, to a lesser extent, by microbial processes in soils. Nitrogen oxides contribute to nitrogen deposition and can have both positive and negative effects on vegetation growth. However, their interaction with other pollutants, such as sulphur dioxide (SO2), can lead to more adverse effects, particularly in urban areas.
Carbon monoxide (CO) is a colourless and odourless gas produced by the incomplete combustion of carbonaceous fuels, including wood, petrol, coal, natural gas, and kerosene. It is commonly found in ambient air due to motor vehicle emissions. Carbon monoxide is dangerous as it impairs the body's ability to bind to oxygen, damaging tissues and cells. Exposure to carbon monoxide can cause breathing difficulties, exhaustion, dizziness, and flu-like symptoms, and high levels can be fatal.
These gaseous pollutants, ozone, nitrogen oxides, and carbon monoxide, are significant contributors to air pollution and pose severe risks to human health and the environment. Reducing emissions and improving air quality are crucial to mitigate their harmful impacts.
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Volatile organic compounds, which vaporize at room temperature
Volatile organic compounds (VOCs) are organic chemical compounds that vaporize at room temperature. They are called organic because they contain carbon. VOCs are released into the air when we use products and materials that contain them. VOCs are given off by paints, cleaning supplies, pesticides, some furnishings, and even craft materials like glue. Gasoline and natural gas are major sources of VOCs, which are released during combustion. VOCs are also emitted during certain activities, like frying or broiling foods, smoking cigarettes or vaping, and using fuel-burning appliances like gas stoves and furnaces.
VOCs are classified as Very Volatile Organic Compounds (VVOCs), Volatile Organic Compounds (VOCs), and Semivolatile Organic Compounds (SVOCs). The classification is based on the volatility or boiling point of the compound. The higher the volatility (or the lower the boiling point), the more likely the compound will be emitted from a product or surface into the air. VOCs with high volatility are difficult to measure and are found almost entirely as gases in the air.
VOCs are a significant source of indoor air pollution, with levels up to ten times higher than outdoors. New buildings experience particularly high levels of VOC off-gassing due to the abundant new materials exposed to indoor air. VOCs are also found in dry-cleaned clothing, with chemicals used in the cleaning process off-gassing long after the cleaning is complete.
Many VOCs react with other compounds in the atmosphere to form ground-level ozone, a major constituent of photochemical smog. In the United States, emissions of VOCs to the outdoors are regulated by the EPA to prevent the formation of ozone and reduce its impact on air quality.
Some VOCs, such as formaldehyde, benzene, and ethylene glycol, are harmful to human health. They are found in various products, including cleaning supplies, air fresheners, cosmetics, paints, markers, and glues. Higher air pollution levels, including VOCs, increase short-term respiratory infections and can lead to more school absences for children.
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Polycyclic aromatic hydrocarbons, organic compounds containing carbon and hydrogen
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds composed of multiple fused aromatic rings of carbon and hydrogen atoms. They are primarily colorless, white, or pale yellow solid compounds. PAHs are organic pollutants that are widespread in the environment, with more than 100 types of PAHs known to be prevalent. They are produced by the incomplete combustion of organic matter, such as engine exhaust fumes, tobacco smoke, incinerators, roasted meats, and forest fires. PAHs can also be found in fossil fuel deposits like coal and petroleum.
PAHs have various sources, including anthropogenic and natural activities. Pyrogenic PAHs, formed through the unintentional incomplete combustion of organic materials at high temperatures, are more concentrated in urban areas due to industrial processes and vehicle emissions. Petrogenic PAHs, on the other hand, are present in petroleum and its by-products, which become widespread during storage, transport, use, and leakage of crude oil.
The molecular arrangements of aromatic rings in PAHs can be linear, angular, or clustered. PAHs are classified into light-molecular weight PAHs (LMW PAHs), which have two or three aromatic rings, and high-molecular weight PAHs (HMW PAHs), which have four or more aromatic rings. LMW PAHs are emitted in the gaseous phase, while HMW PAHs are emitted in particulate form.
PAHs have been linked to adverse health effects, including eye and lung irritation, blood and liver issues, and even cancer. Studies have shown that exposure to PAHs during pregnancy can impact fetal development and lead to slower brain-processing speeds in children. They are considered highly toxic, mutagenic, carcinogenic, and immunotoxicogenic. Additionally, PAHs are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life.
Overall, polycyclic aromatic hydrocarbons are a significant concern in air pollution due to their toxicity and widespread presence in the environment. Their impact on human health and potential role in the development of early life forms make them a subject of ongoing research and regulation.
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Natural sources, like wildfires, dust storms, and volcanic eruptions
Natural sources of air pollution include wildfires, dust storms, and volcanic eruptions. These events can have significant impacts on air quality and human health.
Wildfires
Summertime wildfires can reduce visibility and cause haze in affected areas. The smoke and pollutants released into the air can have negative biological effects on humans and nature.
Dust Storms
Dust storms are characterized by strong winds carrying large amounts of fine dust particles over a wide area. These particles, known as PM2.5, have a diameter of 2.5 micrometers or less and can remain suspended in the air for extended periods. When inhaled, they can penetrate deep into the respiratory system, causing irritation and exacerbating existing conditions such as asthma and COPD. Dust storms can also transport pollutants, allergens, and potentially harmful microorganisms, further compromising air quality and impacting both short-term and long-term health.
Volcanic Eruptions
Volcanic eruptions release large quantities of gases and particles into the atmosphere, including carbon dioxide, sulphur dioxide, and volcanic ash. The extent of the volcanic ash cloud depends on particulate size, wind speed, direction, and eruption type. Smaller particulates allow the ash cloud to extend further, while wind speed and direction determine how far and at what rate the cloud spreads. Volcanic eruptions can also deposit large quantities of sulphuric acid into marine ecosystems and release harmful gases into the air, affecting terrestrial organisms, especially humans. The eruption of Mount St. Helens in 1980, for example, resulted in an international pollution event, with the ash cloud reaching around the world in 15 days.
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Frequently asked questions
Natural sources of air pollution include wildfires, dust storms, and volcanic eruptions.
Human sources of air pollution include the burning of fossil fuels, vehicle emissions, industrial processes, waste management, and agriculture.
The main types of air pollution are particulate matter, carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide.
Air pollution can cause respiratory and other diseases, including strokes, heart disease, lung cancer, asthma, and chronic obstructive pulmonary disease (COPD). It is also associated with oxidative stress and inflammation in human cells, which can lead to chronic diseases and cancer.
