Air Pollutants: What's Harming Our Air?

Air pollution is caused by the release of various gases, finely divided solids, or finely dispersed liquid aerosols into the atmosphere at rates that exceed the environment's capacity to dilute or absorb them. These air pollutants have adverse effects on human health and ecosystems, causing respiratory diseases, cancer, and other serious health issues. The U.S. Clean Air Act identifies six common air pollutants, including particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These criteria pollutants are regulated by the EPA to protect human health and the environment. Other hazardous air pollutants, or air toxics, include asbestos, benzene, and heavy metals, which are suspected of causing cancer and other chronic conditions. Air pollution is a serious issue, with European city dwellers facing unsafe levels of exposure, leading to premature deaths and negative impacts on the environment.

Particulate matter

The size of particulate matter is measured in micrometers, and particles with a diameter of 10 micrometers or less (known as PM10) are considered inhalable. These larger particles can irritate the eyes, nose, and throat and are often associated with the worsening of respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD).

However, the smaller particles, with diameters of 2.5 micrometers or less (PM2.5), pose the greatest risk to health. These fine particles can penetrate deep into the lungs and may even enter the bloodstream. Long-term exposure to PM2.5 has been linked to premature death, particularly in individuals with pre-existing heart or lung conditions. Additionally, PM2.5 is the main cause of reduced visibility (haze) in many parts of the world, including national parks and wilderness areas.

To protect public health, the U.S. Environmental Protection Agency (EPA) regulates particulate matter as one of the six "criteria" air pollutants. The EPA develops limits for these pollutants based on human health and environmental criteria. The Air Quality Index (AQI) is a useful tool that informs individuals about the air quality in their area and provides guidance on taking appropriate actions to protect their health.

Ground-level ozone

Ozone is considered "bad" due to its adverse effects on human health and the environment. Exposure to ground-level ozone has been linked to premature mortality and an array of health issues, especially for children, the elderly, and individuals with lung diseases like asthma. It can trigger asthma attacks, hospital admissions, and other respiratory problems.

In addition to its impacts on human health, ground-level ozone can also damage vegetation and reduce crop productivity. It can injure flowers and shrubs and may contribute to forest decline. Furthermore, it can harm synthetic materials, causing cracks in rubber, accelerating the fading of dyes, and deteriorating paints and coatings.

To address the issues associated with ground-level ozone, the EPA in the United States has implemented regulations and standards. They work with states and tribes to monitor air quality and designate areas as attainment or nonattainment based on national ambient air quality standards. States with nonattainment areas must develop state implementation plans (SIPs) to outline measures for improving air quality. These efforts aim to reduce emissions of pollutants that contribute to ground-level ozone and help governments meet national air quality standards.

Carbon monoxide

Indoors, carbon monoxide can be released by a variety of household items, including unvented kerosene and gas space heaters, leaking chimneys and furnaces, and gas stoves. In homes in developing countries, the burning of biomass fuels and tobacco smoke are the most important sources of exposure to carbon monoxide. Clogged chimneys, wood-burning fireplaces, decorative fireplaces, and supplementary heaters without properly working safety features can also vent carbon monoxide into indoor spaces. Tobacco smoke can be a major source of indoor exposure, as can exhaust from motor vehicles operating in attached garages.

Breathing air with a high concentration of CO reduces the amount of oxygen that can be transported in the blood to critical organs like the heart and brain. At very high levels, which are possible indoors or in other enclosed environments, CO can cause dizziness, confusion, unconsciousness, and even death. While very high levels of CO are not likely to occur outdoors, elevated outdoor CO levels can be of particular concern for people with some types of heart disease. Short-term exposure to elevated CO levels may result in reduced oxygen to the heart, accompanied by chest pain, also known as angina.

Several studies have investigated the health effects of carbon monoxide exposure. For example, Mar et al. evaluated the association between mortality in the elderly and air pollutants over a three-year period in Phoenix, Arizona, finding a significant correlation between total mortality and changes in ambient carbon monoxide and nitrogen dioxide. Chen and Wang reviewed the health effects of carbon monoxide in air pollution in major Chinese cities in 2000.

Nitrogen oxides

Nitrogen dioxide (NO2) is one of the most common nitrogen oxides and is a primary pollutant. It is produced by the combustion of fossil fuels such as coal, oil, and gas, as well as by vehicle emissions, power plants, and off-road equipment. NO2 is a foul-smelling, reddish-brown gas that can irritate the airways and aggravate respiratory diseases, especially asthma. Prolonged exposure to high levels of NO2 can cause irreversible damage to the respiratory system.

Nitric oxide (NO) is another important nitrogen oxide. While it is not considered hazardous under typical ambient conditions, excess NO and its products can have negative health effects, including respiratory ailments, hematologic side effects, metabolic disorders, low blood pressure, nausea, vomiting, and diarrhoea. High levels of NO can also harm vegetation by increasing their susceptibility to diseases and frost damage.

Overall, nitrogen oxides are a significant contributor to air pollution and can have detrimental effects on human health and the environment. It is important to monitor and regulate their emissions to mitigate their impact.

Hazardous air pollutants

These hazardous air pollutants come from a range of sources, including industrial facilities, power plants, refineries, vehicles, and consumer products. For example, ethylene oxide is released from medical equipment sterilization facilities, and perchloroethylene is emitted from certain dry cleaning establishments.

Outdoor air quality has shown improvement since the 1990s, but hazardous air pollutants continue to pose significant challenges to public health. Particle pollution, ground-level ozone, carbon monoxide, nitrogen oxides, and sulfur oxides are among the most common hazardous air pollutants. These pollutants can have detrimental effects on human health, causing irritation to the eyes, nose, and throat, and, in more severe cases, leading to respiratory issues and other serious health complications.

To address these issues, the Clean Air Act mandates that the EPA establish National Ambient Air Quality Standards for six widespread air pollutants, known as "criteria pollutants." These criteria pollutants are regulated based on human health and environmental criteria. While the EPA has made reducing urban air toxics emissions a priority, it is important to recognize that even pollutants not classified as "hazardous" can still be harmful and unsafe.

The impact of hazardous air pollutants extends beyond immediate health concerns. These pollutants can settle into waterways, streams, rivers, and lakes, leading to potential ingestion through drinking water or consumption of fish from these sources. Furthermore, indoor air quality is also affected by hazardous pollutants from tobacco smoke, building materials, and consumer products.

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