Air Pollutants: Five Major Hazards To Breathe Easy

Air pollution is a pressing issue that poses significant risks to both human health and the environment. While various factors contribute to poor air quality, six major air pollutants are of particular concern: particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants, regulated by organizations like the EPA in the US, have far-reaching impacts and are known to cause a range of health issues and environmental degradation. Despite improvements in outdoor air quality over time, these pollutants continue to pose challenges and remain a focus area for regulatory bodies and public health officials.

Ground-level ozone

In contrast, ground-level ozone is considered "bad" due to its negative impact on human health and the environment. It is the main ingredient in smog and is formed by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. These reactions are more common during the summer months when there is more heat and sunlight, leading to higher levels of pollution. Ground-level ozone is not directly emitted into the air but is a byproduct of emissions from cars, power plants, industrial boilers, refineries, and chemical plants. It can also be carried by wind, affecting rural areas as well.

Ozone is a greenhouse gas and the third most important after CO2 and CH4, contributing to global warming. It has various health effects, especially for children, the elderly, and people with lung diseases such as asthma. It can irritate the eyes, nose, and throat, and higher concentrations can lead to respiratory issues and impact the deep parts of the lungs, and even the blood. To protect oneself, it is recommended to plan outdoor activities when ozone levels are lower, usually in the morning or evening, and to spend more time indoors or in less populated areas.

To address the issue of ground-level ozone, the Environmental Protection Agency (EPA) in the United States works with states and tribes to monitor and regulate air quality. They designate areas as attainment or nonattainment based on national ambient air quality standards, and states are required to implement plans to improve air quality in nonattainment areas. These efforts aim to reduce emissions of pollutants that contribute to ground-level ozone and help governments meet national air quality standards.

Particle pollution

The particles that make up particle pollution vary in size. Some are as small as a few microns, while others are one-tenth the diameter of a human hair. The smaller particles, known as PM2.5, can penetrate deep into the respiratory tract, reaching the lungs and causing irritation to the eyes, nose, throat, and lungs. They can also worsen medical conditions like heart disease and asthma and increase the risk of heart attacks. Larger particles, called PM10, are still small enough to irritate the eyes, nose, and throat.

Carbon monoxide

Indoor sources of CO include wood stoves, gas stoves, cigarette smoke, and unvented gas and kerosene space heaters. CO levels tend to be higher during the colder months when inversion conditions are more frequent, trapping air pollution near the ground. Indoor CO levels can be considerably higher than outdoor levels.

The health effects of carbon monoxide are primarily due to its ability to reduce oxygen delivery to the body's organs and tissues. Exposure to carbon monoxide can cause chest pain, reduced exercise capacity, and other cardiovascular effects, particularly in individuals with heart disease. Even healthy individuals can experience adverse effects from high levels of CO, including vision problems, reduced cognitive function, and difficulty performing complex tasks.

To mitigate the health risks associated with carbon monoxide, 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 at safe levels. Additionally, the EPA conducted a review of the National Ambient Air Quality Standard for Carbon Monoxide in 2011, which led to the consideration of CO emission reductions as a potential strategy to combat global warming.

Nitrogen oxides

There are seven oxides of nitrogen that can be found in ambient air, with nitric oxide (NO) and nitrogen dioxide (NO2) being the two principal nitrogen oxides associated with combustion sources. High combustion temperatures result in higher nitric oxide emissions, with 90-95% of nitrogen oxides typically emitted as nitric oxide and only 5-10% as nitrogen dioxide. These gases are emitted from cars, trucks, and other vehicles or machinery that burn fuel, as well as from power plants and other fuel combustion equipment.

Nitrogen dioxide is a highly reactive and foul-smelling gas that can irritate the airways in the human respiratory system. Short-term exposure to high concentrations of NO2 can aggravate respiratory diseases, especially asthma, leading to symptoms such as coughing, wheezing, or difficulty breathing. Longer exposures may contribute to the development of asthma and increase susceptibility to respiratory infections, with children, the elderly, and people with asthma being at greater risk.

Lead

Sources of lead emissions vary from one area to another. At the national level, major sources of lead in the air are ore and metals processing, and piston-engine aircraft operating on leaded aviation fuel. Other sources include waste incinerators, utilities, and lead-acid battery manufacturers. The highest air concentrations of lead are usually found near lead smelters.

Historically, motor vehicles were a major source of lead air emissions, but the phasing out of leaded gasoline has significantly reduced these emissions. As a result of regulatory efforts, levels of lead in the air decreased by 98% between 1980 and 2014.

Humans may be exposed to lead from air pollution through inhalation or by ingesting lead that has settled onto soil or dust. Once in the body, lead distributes throughout the blood and accumulates in the bones. Depending on the level of exposure, lead can have adverse effects on various systems in the body, including the nervous system, kidney function, immune system, reproductive and developmental systems, and the cardiovascular system. Lead exposure can also affect the oxygen-carrying capacity of the blood.

Children are especially sensitive to the effects of lead exposure, which can contribute to behavioural problems, learning deficits, and lowered IQ. In ecosystems, elevated lead levels can result in decreased growth and reproduction in plants and animals, as well as neurological effects in vertebrates.

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