Air Pollutants: Understanding The Many Threats To Our Atmosphere

Air pollution is a pressing issue that affects the health of people and the planet. The World Health Organization (WHO) reports that nearly seven million people die annually due to indoor and outdoor air pollution, with 99% of people currently breathing air that exceeds the recommended guideline limits for pollutants. There are various air pollutants, including common or 'criteria' pollutants, and hazardous air pollutants (HAPs). Criteria pollutants include ground-level ozone, particle pollution, carbon monoxide, nitrogen oxides, sulfur oxides, and lead. HAPs, which are known or suspected to cause cancer and other serious health issues, include benzene, perchloroethylene, and asbestos. Other air pollutants include formaldehyde, radon, mold, and allergens from trees, weeds, and grass, which can be hazardous to human health.

Particulate matter

The size of particulate matter varies, with some particles measuring between 2.5 and 10 micrometers in diameter, known as "inhalable coarse particles" or PM10. These larger particles can irritate the eyes, nose, and throat and are commonly composed of dust from roads, farms, dry riverbeds, construction sites, and mines.

However, the more concerning particles are those designated as PM2.5, with diameters of 2.5 micrometers or less. These fine particles pose the greatest risk to health as they can penetrate deep into the lungs and even enter the bloodstream. The health effects of inhaling these fine particles have been extensively studied, and they include respiratory diseases, cardiovascular issues, developmental and neurodegenerative disorders, and an increased risk of premature death.

The Air Quality Index (AQI) is a useful tool provided by AirNow that helps individuals understand the level of pollution in their outdoor air and take necessary actions to protect their health. The EPA also plays a crucial role in regulating emissions of pollutants that form particulate matter, implementing rules to help state and local governments meet national air quality standards.

The impact of particulate matter on human health is significant, with studies estimating that it contributes to thousands of deaths annually in the United States and hundreds of thousands of premature deaths globally. Fine particle pollution, in particular, has been associated with a large number of these deaths and health problems. As a result, it is crucial to monitor and regulate particulate matter to minimize its harmful effects on human health and the environment.

Ground-level ozone

Ozone is a gas composed of three atoms of oxygen. While stratospheric ozone occurs naturally in the upper atmosphere and protects living things from ultraviolet radiation, ground-level ozone is considered "bad" due to its negative impact on human health and the environment. Exposure to ground-level ozone has been linked to pre-mature mortality and a range of health issues, particularly for children, the elderly, and people with lung diseases such as asthma. It can irritate the eyes, nose, and throat, and even reach the deep parts of the lungs or the bloodstream.

To address the issue of ground-level ozone, the US Environmental Protection Agency (EPA) has implemented regulations to help states reduce ozone levels in outdoor air. These include national and regional rules to reduce emissions of pollutants that form ground-level ozone, as well as air quality standards that areas must meet. If an area does not meet the national standard, it is designated as a "nonattainment area," and the state must develop a plan to improve air quality.

Internationally, the Ozone Annex was added to the Canada-United States Air Quality Agreement in December 2000 to address the transboundary air pollution leading to high levels of ground-level ozone. Ground-level ozone not only affects human health but also has significant impacts on vegetation and crops. It can injure flowers and shrubs and may contribute to forest decline. Additionally, it can damage synthetic materials, textiles, and paints.

Carbon monoxide

CO is a harmful air pollutant that can have adverse effects on human health. When inhaled, it reduces the amount of oxygen that can be transported in the bloodstream to vital organs like the heart and brain. Exposure to carbon monoxide can cause chest pain, reduced exercise capacity, and other cardiovascular issues, especially in individuals with pre-existing heart conditions. Even healthy individuals can experience harmful effects from high levels of CO, including vision problems, reduced ability to work or learn, impaired manual dexterity, and difficulty with complex tasks.

Indoor sources of CO include gas stoves, malfunctioning or improperly vented gas appliances (such as water heaters, furnaces, and clothes dryers), space heaters, fireplaces, tobacco smoke, and car emissions. The highest levels of indoor CO typically occur during colder months when inversion conditions trap air pollution near the ground. Outdoor CO levels are generally safe due to EPA regulations and standards, but elevated levels can be concerning for individuals with heart disease.

To mitigate the harmful effects of CO, the U.S. Environmental Protection Agency (EPA) sets and reviews standards for acceptable CO levels in outdoor air under the Clean Air Act. These standards help state, tribal, and local agencies ensure that CO is maintained at safe levels. Additionally, CO emission reductions are considered a potential strategy to mitigate the effects of global warming, as CO contributes to climate change through chemical reactions that produce ozone, a potent climate change gas.

Nitrogen oxides

Nitrogen dioxide (NO2) and nitric oxide (NO) are the two main nitrogen oxides associated with combustion sources. The higher the combustion temperature, the more nitric oxide is generated. Typically, 90-95% of nitrogen oxides are emitted as nitric oxide, while only 5-10% are emitted as nitrogen dioxide. However, nitric oxide rapidly oxidizes in the air to form nitrogen dioxide, which is why the latter is considered the primary pollutant.

Sulfur oxides

SO2 is a component of smog and acid rain, which can harm sensitive ecosystems, including trees and plants, by damaging foliage and inhibiting growth. It can also contribute to respiratory illness and aggravate existing heart and lung conditions. Like nitrogen dioxide, sulfur dioxide can create secondary pollutants, such as sulfate aerosols, particulate matter, and acid rain, once released into the air.

Other sulfur oxides (e.g., SO3) are found in the atmosphere at much lower concentrations than SO2. However, emissions that lead to high concentrations of SO2 generally also lead to the formation of other SOx. SOx can react with other compounds in the atmosphere to form small particles that contribute to particulate matter (PM) pollution. These particles may penetrate deeply into the lungs and, in sufficient quantities, can cause respiratory issues and other health problems.

The EPA has established national ambient air quality standards for SO2 to protect against exposure to sulfur oxides. These standards are designed to prevent adverse effects on human health and the environment. The EPA also works with state and local governments to identify areas that do not meet SO2 standards and develop plans to reduce SO2 levels.

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