Air Pollutants: What's Not Harming Our Atmosphere?

The Clean Air Act requires the US Environmental Protection Agency (EPA) to set standards for six common pollutants. These pollutants are known as criteria pollutants and are found all over the United States. They include particulate matter (often referred to as particle pollution), ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants can cause harm to human health, the environment, and property damage. While these are common atmospheric pollutants, there are other harmful pollutants that are not specifically regulated in the Clean Air Act, such as toxic organic compounds (TOCs) and volatile organic compounds (VOCs).

Particulate matter

The health risks associated with particulate matter are primarily linked to the size of the particles. Larger particles, such as sand and big dust particles, are typically unable to enter the respiratory system and cause harm. However, smaller particles, classified as PM10 and PM2.5, pose significant health risks. PM10 particles, with diameters of 10 microns or less, can be inhaled into the lungs and induce adverse health effects, particularly for individuals with respiratory conditions. PM2.5 particles, with diameters of 2.5 microns or less, are even more harmful. They can penetrate deep into the lungs and even enter the bloodstream. Long-term exposure to PM2.5 has been linked to premature death, especially in people with chronic heart or lung diseases, and impaired lung development in children.

The sources of PM2.5 and PM10 particles differ, resulting in distinct chemical compositions. PM2.5 particles are primarily produced by the combustion of gasoline, oil, diesel fuel, or wood. They are also emitted from construction sites, landfills, agriculture, wildfires, and industrial processes. In contrast, PM10 particles include dust from various sources, such as construction, landfills, agriculture, wildfires, industrial emissions, wind-blown dust, pollen, and bacterial fragments.

To address the health risks associated with particulate matter, the United States Environmental Protection Agency (EPA) has implemented measures to regulate and reduce emissions of pollutants that contribute to PM. The EPA's national and regional rules aim to assist state and local governments in meeting the Agency's national air quality standards. Additionally, the Air Quality Index (AQI) provides daily information on outdoor air quality and associated health risks, helping individuals take necessary precautions to protect their health.

Ground-level ozone

Ozone is a gas composed of three oxygen atoms. Depending on where it is found in the atmosphere, it can be either "good" or "bad". Stratospheric ozone is "good" because it occurs naturally in the upper atmosphere and forms a protective layer that acts as a shield from the sun's harmful ultraviolet rays. This "good" ozone has been partially destroyed by man-made chemicals, creating what is known as a "hole in the ozone".

To address this issue, the US Environmental Protection Agency (EPA) has established regulations and standards for ground-level ozone. These include National Ambient Air Quality Standards (NAAQS) and state implementation plans (SIPs) to improve air quality in areas that do not meet the standards. EPA's rules aim to reduce emissions of pollutants that contribute to ground-level ozone, helping state and local governments achieve the Agency's air quality standards.

Carbon monoxide

The U.S. Environmental Protection Agency (EPA) is tasked with setting National Ambient Air Quality Standards (NAAQS) for six common air pollutants, including CO, under the Clean Air Act (CAA). These standards are based on health and environmental criteria to ensure that CO levels remain safe for humans and the environment.

CO is harmful to both health and air quality. At low levels, it can exacerbate cardiovascular disease, while at high levels, it can damage the central nervous system. Extremely high levels of CO are poisonous and can lead to death. Therefore, regulatory efforts are crucial to mitigate the adverse impacts of CO pollution.

Areas with heavy traffic congestion typically experience higher levels of CO. Local, state, and tribal agencies collaborate with the EPA to implement and maintain air quality standards that help reduce CO pollution. These collective efforts are essential to safeguard public health and minimise the environmental consequences associated with CO emissions.

In summary, carbon monoxide (CO) is a significant atmospheric pollutant that poses risks to human health and the environment. Regulatory measures, such as those implemented by the EPA and other agencies, play a critical role in managing CO emissions and mitigating their potential harm. Continuous monitoring and adherence to air quality standards are necessary to ensure the well-being of communities and ecosystems affected by this invisible and odourless atmospheric pollutant.

Sulfur dioxide

SO2 is a major air pollutant and is harmful to both human health and the environment. In the atmosphere, SO2 can react with other compounds to form small particles that contribute to particulate matter (PM) pollution. These particles can penetrate deeply into the lungs and, in sufficient quantities, can cause respiratory issues and other health problems. SO2 and other sulfur oxides are also a major component of acid rain, which can harm sensitive ecosystems.

The largest source of SO2 emissions is the burning of fossil fuels, particularly by power plants and other industrial facilities. Control measures that reduce SO2 emissions can generally be expected to reduce people's exposure to all gaseous sulfur oxides. This may also have the co-benefit of reducing the formation of particulate sulfur pollutants, such as fine sulfate particles.

To protect human health and the environment, the United States Environmental Protection Agency (EPA) has established national ambient air quality standards for SO2. These standards are designed to reduce SO2 emissions and help state and local governments meet the Agency's broader air quality goals. EPA's rules to reduce SO2 emissions include identifying areas where air quality does not meet SO2 standards and working with state, local, and tribal governments to develop plans to reduce SO2 levels.

Nitrogen dioxide

NO2 is not only harmful to human health but also contributes to the formation of other pollutants, known as secondary pollutants. These include ozone, particulate matter (PM), acid rain, and other toxic chemicals. Ozone, in particular, is a powerful oxidant that can reduce lung function, aggravate asthma, increase the chances of respiratory illness, and even lead to permanent lung damage. It also damages plant life and reduces farm yields.

To address the issue of NO2 pollution, many cities have implemented measures to reduce traffic-related air pollution. For example, London's Ultra Low Emission Zone initiative resulted in a 36% reduction in NO2 levels in the first six months after its launch in 2019. High-income countries are also experiencing a rapid decline in NO2 exposures due to sustained policy action and technological advancements.

While progress is being made, nitrogen dioxide remains a significant atmospheric pollutant, posing health risks and environmental challenges worldwide. It is important to continue efforts to reduce NO2 emissions and improve air quality to protect public health and mitigate the negative impacts of this common pollutant.

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