Air Pollutants: Criteria For Clean Air

Air pollution is a major global public health risk factor, causing 6.7 million premature deaths annually, according to the World Health Organization (WHO). In 2021, the WHO updated its 2005 Global Air Quality Guidelines (AQG) to address the large impact of air pollution on global health. These guidelines provide uniform targets for air quality and are addressed to all countries of the world. In the United States, the Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as criteria air pollutants. These pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead, and they can have harmful effects on both human health and the environment.

Health risks

The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants known as "criteria air pollutants". These pollutants are particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are harmful to human health, especially for sensitive populations such as asthmatics, children, and the elderly.

Particulate matter, also known as particle pollution, is made up of tiny pieces of solids or liquids in the air. These particles can be large enough to be visible, like smoke, or so small that they are invisible. When inhaled, these particles can irritate the eyes, nose, and throat, and the smaller particles can penetrate deep into the lungs and even enter the bloodstream. This can lead to cardiovascular and respiratory issues, such as ischaemic heart disease and stroke, and has been linked to adverse perinatal outcomes and lung cancer. Long-term exposure to particulate matter is associated with increased morbidity and mortality from cardiovascular and respiratory diseases.

Ground-level ozone is another major health threat among the criteria air pollutants. Ozone in the upper atmosphere protects us from the sun's ultraviolet rays, but at ground level, it is a harmful pollutant and a key component of smog. Breathing in ground-level ozone can cause chest pain, coughing, throat irritation, and airway inflammation, as well as reduce lung function and harm lung tissue. It can also worsen respiratory conditions such as bronchitis, emphysema, and asthma. People with asthma, children, older adults, and those who spend a lot of time outdoors are particularly vulnerable to the harmful effects of ground-level ozone.

Carbon monoxide, sulfur dioxide, and nitrogen dioxide are additional criteria air pollutants that pose significant health risks. Exposure to these pollutants can lead to a range of health problems, with nitrogen dioxide being a strong oxidant and soluble in water. Furthermore, there is no safe threshold for some of these pollutants, meaning that any level of exposure can potentially cause adverse health effects.

The health risks associated with these criteria air pollutants are well documented, and they contribute to millions of premature deaths each year. The EPA sets standards and regulations to protect public health and welfare, but it is important for individuals to be aware of the potential dangers and take necessary precautions to minimize their exposure to these harmful pollutants.

Environmental impact

Air pollution is the greatest environmental threat to health, and it poses a significant threat to people worldwide. According to the World Health Organization (WHO), there are 7 million premature deaths every year due to the combined effects of outdoor and household air pollution, with millions more falling ill from breathing polluted air.

The WHO Air Quality Guidelines are a set of evidence-based recommendations of limit values for specific air pollutants. These guidelines are designed to offer guidance in reducing the health impacts of air pollution based on expert evaluations of current scientific evidence. They are not legally binding standards but are intended to be used in diverse conditions in all WHO regions to support a broad range of policy options for air quality management.

The six common air pollutants, also known as "criteria air pollutants", include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These criteria air pollutants are found all over the United States and much of the world. They are generally combustion products released by the burning of fossil fuels. For example, sulfur dioxide (SO2) largely comes from burning fossil fuels like coal and oil in power plants and industrial facilities, as well as burning diesel fuel in vehicles. Short-term exposure to SO2 can harm the human respiratory system, and elevated concentrations can contribute to particulate matter pollution, reduce visibility, and cause regional haze. At high concentrations, gaseous sulfur oxides can harm trees and plants by damaging foliage and decreasing growth as a result of acid rain.

Particulate matter (PM) is another significant pollutant, with fine particles (PM2.5) capable of penetrating deep into the lungs and entering the bloodstream, causing adverse health effects such as cardiovascular disease, stroke, and respiratory issues. The sources of particulate matter vary depending on location, but typically include traffic and transportation, industrial activities, power plants, construction sites, waste burning, fires, or fields.

In summary, the environmental impact of air pollutants is far-reaching, with criteria air pollutants causing harm to human health, the environment, and property damage. The WHO Air Quality Guidelines play a crucial role in providing evidence-based recommendations to reduce the health impacts of these pollutants and protect public health.

Policy and regulation

Air pollution is a major environmental health problem affecting people in low-, middle-, and high-income countries. The World Health Organization (WHO) estimates that one out of every nine deaths worldwide is the result of ambient air pollution-related conditions. In 2019, outdoor and household air pollution together accounted for approximately 12% of all deaths worldwide. The latest burden estimates reflect the significant role of air pollution in cardiovascular illness and death.

The WHO has been working to address this issue by updating its global air quality guidelines, which provide uniform targets for air quality to all countries. The guidelines, which were last updated in 2021, set targets for particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). These targets are much stricter than most national standards, and if applied, could save numerous lives. For example, in the European Union alone, exposure to fine particulate matter (PM2.5) caused approximately 307,000 premature deaths in 2019. The WHO recommends a maximum exposure of 10 µg/m3 for PM2.5, while the EU's current limit is 25 µg/m3.

To reduce air pollution, the WHO and other organizations have proposed several policies and regulations. These include:

• Cleaner technologies in industries to reduce industrial smokestack emissions.
• Improved management of urban and agricultural waste, including capturing methane gas emitted from waste sites and using it as biogas instead of incinerating it.
• Ensuring access to affordable clean household energy solutions for cooking, heating, and lighting.
• Prioritizing cleaner modes of power generation and promoting the use of renewable, combustion-free power sources such as solar and wind energy.
• Promoting sustainable mobility and prioritizing rapid urban transit, walking, and cycling networks in cities, as well as improving the energy efficiency of buildings.
• Reducing emissions of pollutants from traffic and heating, and expanding urban green spaces, such as planting trees.

The implementation of these policies and regulations has the potential to significantly reduce air pollution and improve public health. In the United States, for example, the benefits of the Clean Air Act are estimated to be around 30 times greater than the costs, resulting in improved economic growth and population welfare. Similarly, in China, public health benefits were found to be 50% greater than the costs of air quality improvement measures.

Industry and energy

Industrial activities and energy generation are major sources of air pollution. The World Health Organization (WHO) has developed Air Quality Guidelines (AQG) to help countries improve air quality and protect public health. These guidelines are based on scientific evidence and are designed to reduce the health impacts of air pollution.

Industrial processes, such as high-temperature combustion of fuels, can release various pollutants into the air. Nitrogen dioxide (NO2), a reddish-brown and water-soluble gas, is one such pollutant. It is an irritant to the airways and can aggravate respiratory diseases. NO2 is produced during combustion processes used for heating, transportation, industrial activities, and power generation. It is also an important precursor to ozone, another pollutant linked to asthma and respiratory conditions.

Particulate matter (PM) is another significant pollutant from industrial and energy sources. PM consists of inhalable particles composed of sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust, or water. The size of PM varies, with PM2.5 and PM10 being the most common in regulatory frameworks due to their health relevance. Industrial activities and power generation facilities contribute to ambient air pollution by emitting PM2.5, which can penetrate deep into the lungs and enter the bloodstream, causing cardiovascular and respiratory issues. Long-term exposure to PM has also been linked to adverse perinatal outcomes and lung cancer.

Additionally, energy generation activities, particularly the burning of fossil fuels (coal, oil, and diesel) by power plants and industrial facilities, are major sources of sulfur dioxide (SO2) emissions. SO2, along with carbon monoxide (CO) and nitrogen oxides (NOx), are pollutants that contribute to the formation of ground-level ozone (O3). O3 is a major component of smog and is formed through photochemical reactions with volatile organic compounds and other pollutants emitted from vehicles and industrial processes.

Addressing air pollution from industry and energy sources is crucial for improving air quality and protecting public health. By following the WHO's AQG and implementing policies in energy, waste management, agriculture, and urban planning, significant health benefits can be achieved by reducing populations' exposure to harmful pollutants.

Transport

Air pollution is a complex mixture of solid particles, liquid droplets, and gases. It can originate from various sources, such as household fuel burning, industrial chimneys, traffic exhausts, power generation, waste burning, agricultural practices, and more. Transport is a significant contributor to air pollution, and efforts to reduce transport-related emissions have had varying levels of success.

The World Health Organization's Air Quality Guidelines (AQG) provide global targets for governments to strive towards improving air quality and protecting their citizens' health. While these guidelines are not legally binding, they offer valuable guidance in mitigating the health impacts of air pollution based on scientific evidence.

The Ozone Transport Region (OTR) in the United States includes states like New Hampshire, which must submit State Implementation Plans (SIPs) for ozone-forming pollutants regardless of their attainment status. This region recognizes the importance of addressing ground-level ozone as a harmful air pollutant that poses risks to vulnerable individuals, including those with asthma, children, older adults, and outdoor workers.

To effectively tackle transport-related air pollution, a comprehensive approach is necessary. This includes implementing policies and measures in the transport sector, such as adapting pollution reduction technologies from the road sector to marine diesel engines in the maritime sector. Additionally, the increasing relevance of non-exhaust emissions, such as those from brake and tyre wear or road abrasion, should be addressed. By combining efforts across different sectors and focusing on evidence-based recommendations, significant health benefits can be achieved by reducing populations' exposure to air pollution from transport activities.

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