Air Pollutants: 4 Most Common Toxins In Our Air

Air pollution is a pressing issue that affects billions of people worldwide. According to the World Health Organization (WHO), 99% of the global population breathes air that exceeds healthy air quality guidelines, leading to various health issues and even premature deaths. While there are numerous air pollutants, this article will focus on the four most common ones: particulate matter (often referred to as particle pollution), ground-level ozone, carbon monoxide, and nitrogen dioxide. These pollutants are not only harmful to human health but also have significant impacts on the environment and contribute to property damage. Understanding these four common air pollutants is crucial in our efforts to improve air quality and protect public health.

Particulate matter (PM)

PM is classified according to the diameter of the particles. Particles with a diameter of 10 micrometres or less (known as PM10) can be inhaled into the lungs and cause adverse health effects. Fine particulate matter, or PM2.5, refers to particles with a diameter of 2.5 micrometres or less, which pose the greatest risk to health. These particles are so small that they can get deep into the lungs and even enter the bloodstream. Long-term exposure to PM2.5 has been linked to premature death, particularly in people with pre-existing heart or lung conditions, and reduced lung function development in children. It is also the main cause of reduced visibility (haze) in some regions of the United States.

The sources of PM10 and PM2.5 are often different, and the two types of particles have distinct chemical compositions. PM2.5 particles are primarily emitted directly from sources, while most PM10 particles form in the atmosphere as a result of chemical reactions. PM2.5 particles are more likely to come from indoor sources and enter buildings through doors, windows, or small gaps in the structure.

To protect yourself from harmful levels of PM, you can refer to daily Air Quality Index (AQI) reports, which indicate the cleanliness or pollution levels of the outdoor air and provide information on associated health risks. The EPA also provides national and regional guidelines to reduce emissions of pollutants that contribute to PM, helping state and local governments meet national air quality standards.

Ground-level ozone

Ozone is often referred to as "good" or "bad" depending on its location in the atmosphere. While stratospheric ozone is considered "good" because it protects living things from the sun's harmful ultraviolet rays, ground-level ozone is categorized as "bad" due to its negative impacts on health and the environment. Ground-level ozone is the main ingredient in smog, which is a harmful mixture of pollutants that affects air quality and visibility.

To address the issue of ground-level ozone, the United States Environmental Protection Agency (EPA) has implemented regulations and standards to reduce ozone levels in outdoor air. The EPA works with states, tribes, and local air agencies to attain National Ambient Air Quality Standards (NAAQS) and improve air quality in areas that do not meet the standards. These regulations aim to reduce emissions of pollutants that contribute to the formation of ground-level ozone, thereby improving air quality and protecting public health.

In addition to its impact on human health, ground-level ozone can also affect vegetation and crops. It can injure flowers, shrubs, and trees, contributing to forest decline in certain regions. Furthermore, ozone can damage synthetic materials, cause cracks in rubber, accelerate the fading of dyes, and deteriorate paints and coatings. These effects have economic implications for industries that rely on these materials and products.

Carbon monoxide

CO pollution occurs primarily from emissions produced by fossil fuel-powered engines, including motor vehicles and non-road engines and vehicles such as construction equipment and boats. Higher levels of CO generally occur in areas with heavy traffic congestion. Other sources of CO emissions include industrial processes such as metal processing and chemical manufacturing, residential wood burning, and natural sources like forest fires.

Indoor sources of CO include wood stoves, gas stoves, malfunctioning or improperly vented gas appliances (e.g. water heaters, furnaces, clothes dryers), space heaters, fireplaces, tobacco smoke, and car emissions. The highest levels of CO typically occur during the colder months when inversion conditions are more frequent, trapping air pollution near the ground beneath a layer of warm air.

CO can have harmful health effects by reducing oxygen delivery to the body's organs and tissues. Exposure to lower levels of CO is particularly serious for those with heart disease, potentially causing chest pain, reduced exercise capacity, and other cardiovascular complications with repeated exposure. Even healthy individuals can experience negative effects from high levels of CO exposure, including vision problems, reduced ability to work or learn, impaired manual dexterity, and difficulty performing complex tasks.

To mitigate the health risks associated with CO, the U.S. Environmental Protection Agency (EPA) sets and reviews standards for CO in outdoor air under the Clean Air Act. These standards help state, tribal, and local agencies ensure that CO levels are maintained within safe limits.

Nitrogen dioxides

Nitrogen dioxide (NO2) is a reddish-brown gas that is soluble in water and a strong oxidant. It is produced from the burning of fossil fuels for transportation, power generation, and industrial activity, as well as from wildfires. Nitrogen dioxide is a harmful pollutant that can irritate airways and aggravate respiratory diseases. It plays a significant role in the formation of ground-level ozone and particulate matter pollution, which are closely linked to asthma and other respiratory conditions.

Nitrogen dioxide is monitored by the Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument, which measures sunlight reflected and scattered off the Earth's surface, clouds, and the atmosphere. TEMPO has revealed high levels of nitrogen dioxide over multiple urban areas across North America, including cities, major highways, and regions such as D.C./Philadelphia/New York City and Dallas/Houston/New Orleans. The measurements show that pollution levels fluctuate throughout the day, with morning pollution often dissipating and then rising again during the second rush hour.

As an air pollutant, nitrogen dioxide has significant health impacts. It is capable of penetrating deep into the lungs and entering the bloodstream, causing cardiovascular and cerebrovascular issues such as ischaemic heart disease and stroke. Both short-term and long-term exposure to nitrogen dioxide have been associated with morbidity and mortality from cardiovascular and respiratory diseases. Long-term exposure has also been linked to adverse perinatal outcomes and lung cancer.

The primary sources of nitrogen dioxide pollution are high-temperature combustion processes used for heating, transportation, industrial activities, and power generation. Household sources of nitrogen oxides (NOx) include fuel-burning equipment such as furnaces, fireplaces, and gas stoves and ovens. Incomplete combustion of fuels and chemical reactions between gases are significant contributors to both ambient and household air pollution.

To address nitrogen dioxide pollution, regulations such as the Clean Air Act in the United States have been implemented. The Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for criteria air pollutants, including nitrogen dioxide. These standards are then worked towards throughout the country in collaboration with state, tribal, and local air agencies.

Sulfur oxides

SO2 is a major air pollutant and is the focus of EPA regulations aimed at reducing people's exposure to SOx. High concentrations of SO2 in the air can lead to the formation of other SOx gases, which can have adverse health and environmental effects. These gases can react with other atmospheric compounds to form small particles, contributing to particulate matter (PM) pollution. These particles can penetrate deep into the lungs, causing respiratory issues and potentially entering the bloodstream, leading to cardiovascular and cerebrovascular problems. Long-term exposure to PM has been linked to adverse perinatal outcomes and lung cancer.

In addition to the health risks, SO2 and other SOx contribute to acid rain, which can damage trees, inhibit plant growth, and harm sensitive ecosystems and waterways. SOx can also react with other compounds to form fine particles that reduce visibility (haze) and stain and damage stone and other materials, including culturally significant objects.

To address these concerns, the EPA has established national and regional rules to reduce SO2 emissions and other pollutants that form SOx. These regulations are designed to help state and local governments meet the Agency's national air quality standards and protect public health and the environment.

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