Air Quality Criteria: Understanding Key Pollutants

The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards for six common air pollutants. These pollutants, also known as criteria air pollutants, are particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are harmful to human health, the environment, and property. The EPA categorises particle pollution into two groups: PM 10 or Inhalable coarse particles, and PM 2.5 or Fine particles. Ground-level ozone is the primary constituent of smog and is created by chemical reactions between oxides of nitrogen and volatile organic compounds in the presence of sunlight.

Ground-level ozone is the primary constituent of smog and is created by chemical reactions between oxides of nitrogen and volatile organic compounds

Ground-level ozone is a harmful air pollutant and the main ingredient in smog. It is not emitted directly into the air but is instead created by chemical reactions between volatile organic compounds (VOCs) and oxides of nitrogen (NOx) in the presence of sunlight. VOCs and NOx are emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources. These chemical reactions occur most efficiently during the summer months when the days are longer, sunlight is stronger, and temperatures are warmest.

Ozone in the air we breathe can harm our health, especially on hot, sunny days when ozone levels can reach unhealthy levels. Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels. Breathing ozone can reduce lung function and inflame lung linings, triggering a variety of health problems, including chest pain, coughing, throat irritation, and congestion. It can also worsen pre-existing conditions like bronchitis, emphysema, and asthma. Repeated exposure may permanently scar lung tissue.

People with lung disease, older adults, people who are active outdoors, and especially children, may be particularly sensitive to ozone. Ozone has two properties of interest to human health. Firstly, it absorbs UV light, reducing human exposure to harmful UV radiation that causes skin cancer and cataracts. Secondly, when inhaled, it reacts chemically with many biological molecules in the respiratory tract, leading to adverse health effects.

To improve air quality, states must draft a plan known as a state implementation plan (SIP) to address nonattainment areas, or areas that do not meet the national ambient air quality standards. The plan outlines the measures the state will take to improve air quality. Once a nonattainment area meets the standards, the EPA designates the area as a "maintenance area." The EPA's national and regional rules to reduce emissions of pollutants that form ground-level ozone help state and local governments meet the Agency's national air quality standards.

Particle pollution, or PM, is a mixture of small particles and liquid droplets that can be from natural or human-made sources

Particle pollution, also known as particulate matter (PM), is a complex mixture of solid particles and liquid droplets found in the air. These particles are often so small that they can be inhaled, causing serious health issues. PM is categorised by particle size, with PM10 referring to particles smaller than 10 micrometers in diameter, and PM2.5 referring to particles 2.5 micrometers or smaller in diameter. These particles can be directly emitted from sources or formed in the atmosphere through chemical reactions.

Sources of particle pollution can be natural or human-made. Natural sources include pollen, wildfires, dust, sea salt, and volcanic eruptions. Human-made sources, on the other hand, include charbroiling, construction equipment, trains, vehicle exhausts, and more. The size of the particles is directly linked to their potential health hazards. Smaller particles, such as PM2.5, can penetrate deeper into the respiratory system, even reaching the bloodstream.

PM2.5 particles are associated with a range of adverse health effects, including premature mortality, increased hospital admissions for heart or lung-related issues, acute and chronic bronchitis, asthma attacks, and respiratory symptoms. They are also the main cause of reduced visibility (haze) in many parts of the United States, including national parks and wilderness areas. Human activities, such as the combustion of fossil fuels and industrial processes, contribute significantly to PM2.5 pollution in outdoor air.

While PM10 particles are larger and less likely to be inhaled into the lungs, they can still have negative health impacts, especially on individuals with pre-existing respiratory or cardiovascular conditions. Sources of PM10 particles include construction sites, agricultural activities, wildfires, industrial emissions, and wind-blown dust.

It is important to note that particle pollution is one of the six widespread air pollutants regulated by national air quality standards. These standards aim to limit the levels of particle pollution in outdoor air to protect human health and the environment.

Carbon monoxide is a colourless, odourless gas produced by the incomplete combustion of fossil fuels

Carbon monoxide (CO) is a colourless, odourless, and highly toxic gas. It is produced when carbon does not fully oxidise during the incomplete combustion of fossil fuels, resulting in the formation of soot or carbon monoxide. In this process, carbon and hydrogen atoms in the fossil fuels react with oxygen, but due to insufficient oxygen, the carbon is only partially oxidised, leading to the creation of carbon monoxide instead of carbon dioxide. This incomplete combustion is inefficient and dangerous, as carbon monoxide is a significant health hazard.

The Clean Air Act mandates that the EPA establish National Ambient Air Quality Standards for six common air pollutants, also known as "criteria air pollutants". Carbon monoxide is one of these criteria air pollutants, which also include particle pollution, ground-level ozone, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are harmful to human health, the environment, and can cause property damage.

Carbon monoxide is particularly dangerous because it is challenging to detect due to its colourless and odourless nature. It is highly poisonous, even at low concentrations of 0.1% (1000 parts per million). Prolonged exposure to carbon monoxide can be fatal, as it binds strongly with haemoglobin in red blood cells, preventing them from carrying sufficient oxygen throughout the body. This property has made it a poison of choice for suicides and, unfortunately, in historical events such as its use by Nazis in WWII death camps.

The incomplete combustion of fossil fuels, primarily from mobile sources of air pollution like passenger vehicles, transit trucks, and construction equipment, is a significant contributor to carbon monoxide production. Simple actions, such as placing a cold pan on a stove burner or blowing air across an unvented burner, can also increase carbon monoxide output. Additionally, holes in heat exchangers and improperly maintained gas appliances can lead to carbon monoxide leaks, posing a severe health risk to occupants.

To address the dangers of carbon monoxide, the law in the UK now requires annual inspections of boilers, gas cookers, and gas fires by registered engineers. Additionally, hardware stores offer special spots impregnated with palladium compounds that darken when exposed to carbon monoxide, making detection easier. Understanding the hazards of carbon monoxide and taking preventive measures are crucial to ensure the safety of individuals and the environment.

Sulfur dioxide and nitrogen dioxide are two of the six criteria air pollutants

The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards for six common air pollutants. These pollutants, also known as "criteria air pollutants", are found all over the United States and can harm human health, the environment, and cause property damage. Sulfur dioxide and nitrogen dioxide are two of these six criteria air pollutants.

Sulfur dioxide (SO2) is a gaseous air pollutant composed of sulfur and oxygen. It is formed when sulfur-containing fuels such as coal, petroleum oil, or diesel are burned. The largest sources of SO2 emissions are from fossil fuel combustion at power plants and other industrial facilities. As of 2020, human-made sources in the U.S. emitted about 1.8 million short tons of sulfur dioxide per year, mainly from burning fuels. Power plants, commercial and institutional boilers, internal combustion engines, and industrial processes such as petroleum refining and metal processing are the largest sources of emissions. SO2 emissions can lead to the formation of other sulfur oxides (SOx) in the atmosphere, which can contribute to particulate matter (PM) pollution and acid rain. SO2 can also react with other compounds in the atmosphere to form fine particles that reduce visibility and damage materials such as stone, statues, and monuments. Long-term exposure to high levels of SO2 can cause respiratory symptoms and reduce lung function, while short exposures to peak levels can make it difficult for people with asthma to breathe during physical activity.

Nitrogen dioxide (NO2) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). It is formed from the burning of fuel, primarily from emissions from cars, trucks, buses, power plants, and off-road equipment. Breathing air with high concentrations of NO2 can irritate the airways and aggravate respiratory diseases, especially asthma. Longer exposures to elevated NO2 levels may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. The nitrate particles that result from NOx make the air hazy and difficult to see through, affecting visibility in many national parks.

To protect human health and the environment, the EPA has established national and regional rules to reduce emissions of SO2 and NO2. These rules help state and local governments meet the Agency's national air quality standards. The EPA identifies areas where the air quality does not meet the standards and works with local governments to develop plans to reduce the amount of these pollutants in the air.

Lead is one of the six criteria air pollutants that can harm health, the environment, and cause property damage

Lead is one of the six criteria air pollutants that can have detrimental effects on human health, the environment, and property. The six criteria air pollutants, as defined by the EPA, include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are common across the United States and are known to cause significant harm.

Lead is a naturally occurring toxic metal found in the Earth's crust. Its widespread use, particularly in the automotive sector, has led to extensive environmental contamination and severe health issues. Lead was previously used in gasoline, resulting in large amounts of lead emissions from vehicles. While lead has been phased out of gasoline, it is still present in the soil, especially in urban areas, and can resuspend into the air.

The harmful health effects of lead exposure are well-documented. Lead is known to accumulate in the body, especially in the bones, and can cause serious health problems over time. Young children are especially vulnerable to lead poisoning, which can severely impact their mental and physical development. Lead exposure during pregnancy can also cause adverse effects on fetal development, increasing the risk of reduced fetal growth and preterm birth. In children, lead exposure can cause permanent brain damage, reduced intelligence, behavioural problems, and impaired educational attainment. Additionally, lead poisoning can lead to a range of health issues in both children and adults, including kidney damage, nervous system disorders, high blood pressure, and reproductive problems.

The presence of lead in the environment contributes to extensive environmental contamination. Lead accumulates in soils and sediments through air emissions, waste discharge, mining activities, and erosion. It persists in the environment and can be resuspended into the air, leading to air pollution and further contamination. Lead has also been known to contaminate drinking water supplies through lead pipes, solders, and fittings, posing risks to human health.

In summary, lead is a significant health and environmental hazard. Its inclusion as one of the six criteria air pollutants underscores the importance of regulating and reducing lead emissions to protect human health, the environment, and property. While progress has been made in reducing lead exposure, it continues to pose a serious threat, highlighting the need for ongoing efforts to mitigate its harmful impacts.

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