Air Quality: Criteria Pollutants And Their Impact

Air pollution is a pressing issue that affects the health of people and the environment, and it also causes property damage. The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also known as criteria air pollutants. These pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are found all over the United States and are known to have detrimental effects on human health, causing respiratory issues and aggravating existing conditions such as asthma. To address this, the EPA establishes standards and regulations to control and reduce the presence of these harmful substances in the air, with the goal of improving air quality and protecting public health.

Particulate matter

PM10 and PM2.5 often derive from different emission sources and have different chemical compositions. PM10 is inhalable into the lungs and can induce adverse health effects. PM2.5 is associated with the greatest proportion of adverse health effects related to air pollution, both in the United States and worldwide. Short-term exposures to PM10 have been linked to the worsening of respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Long-term exposure to PM2.5 has been connected to premature death, especially in people with chronic heart or lung diseases, and reduced lung function growth in children.

The sources of PM are both natural and anthropogenic. Manmade sources include combustion in mechanical and industrial processes, vehicle emissions, and tobacco smoke. Natural sources include volcanoes, fires, dust storms, and aerosolized sea salt. Indoor sources of PM include biological components, such as pollen, mould spores, dust mites, and cockroaches. Indoor activities, such as smoking tobacco, cooking, and burning wood, candles, or incense, also generate PM. Additionally, particles can form indoors from complex reactions of gaseous pollutants emitted from household cleaning products and air fresheners.

The health effects of PM are significant. The World Health Organization estimates that PM air pollution contributes to approximately 800,000 premature deaths each year, ranking it as the 13th leading cause of mortality worldwide. PM has been linked to cardiovascular and cerebrovascular disease through mechanisms such as systemic inflammation, coagulation activation, and direct translocation into systemic circulation. It can also worsen respiratory conditions and increase susceptibility to respiratory infections.

Ground-level ozone

Ozone is a gas composed of three atoms of oxygen. It occurs naturally in the upper atmosphere, where it forms a protective layer that acts as a shield against the sun's harmful ultraviolet rays. This ozone layer has been partially destroyed by man-made chemicals, creating a "hole in the ozone".

The formation of ground-level ozone is influenced by factors such as heat and sunlight, with higher levels typically occurring during the summer months. It is also affected by wind patterns, which can transport ozone over long distances, leading to high ozone levels even in rural areas. Additionally, the concentration of ground-level ozone is influenced by the presence of nitrogen monoxide (NO), which can initiate a chain reaction that increases ozone levels in the atmosphere.

To address the harmful effects of ground-level ozone, states develop implementation plans to reduce emissions and improve air quality. These plans outline specific measures to be taken, such as regulating emissions from vehicles, power plants, and industrial sources. By implementing these plans and following EPA regulations, states can effectively reduce ground-level ozone levels and mitigate their impact on human health and the environment.

Carbon monoxide

In the past, certain areas of the US have been designated as nonattainment for the carbon monoxide NAAQS, indicating that the air quality in those regions did not meet the required standards. However, through various measures such as federal tailpipe standards for new automobiles, traffic flow improvements, and emissions inspection programs, significant improvements have been made in reducing carbon monoxide levels. As a result, many areas, including New Hampshire, have achieved and maintained attainment status for the carbon monoxide NAAQS.

It is important to continue monitoring and regulating carbon monoxide levels to ensure that air quality meets the necessary standards. High concentrations of carbon monoxide in the air can have detrimental effects on human health, particularly for sensitive populations such as people with asthma, children, and the elderly. Additionally, carbon monoxide contributes to the formation of smog and has negative impacts on the environment, including damage to crops, vegetation, and buildings. By adhering to the NAAQS and implementing measures to reduce carbon monoxide emissions, we can protect public health and welfare and mitigate the harmful effects of this criteria air pollutant.

Nitrogen dioxide

NO2 emissions contribute to particle pollution and the formation of ozone or "smog." It can irritate the airways, aggravate respiratory diseases, especially asthma, and lead to respiratory symptoms such as coughing, wheezing, or difficulty breathing. Short-term exposures to high concentrations of NO2 can result in hospital admissions and emergency room visits. Longer exposures to elevated NO2 levels may contribute to the development of asthma and increase susceptibility to respiratory infections.

According to the WHO Guidelines for Indoor Air Quality, indoor sources of nitrogen dioxide include tobacco smoke and gas-, wood-, oil-, kerosene-, and coal-burning appliances such as stoves, ovens, heaters, and fireplaces, particularly those that are unflued or poorly maintained. A Canadian study found that the use of unvented gas stoves was associated with higher NO2 concentrations, while another study in Ethiopia reported a mean 24-hour concentration of 97 μg/m3 in households that primarily used wood, crop residues, and animal dung as fuel.

To reduce NO2 pollution, the EPA has implemented national and regional rules to help state and local governments meet the National Ambient Air Quality Standard (NAAQS). These regulations aim to reduce emissions from various sources, including power plants, industrial sites, and on-road vehicles, leading to improvements in air quality across the nation.

Lead

Historically, motor vehicles and industrial sources were the primary contributors to lead air emissions. The phasing out of leaded gasoline for motor vehicles has significantly reduced lead emissions, yet lead remains present in general-aviation gasoline for piston-engine aircraft. As a result of regulatory efforts, such as the removal of lead from motor vehicle gasoline, the levels of lead in the air nationally have decreased by 98% between 1980 and 2014.

The health effects of lead exposure depend on the level and duration of exposure. Lead can adversely affect multiple 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. Infants, young children, and sensitive populations such as asthmatics are particularly vulnerable to the harmful effects of lead. Even low levels of lead exposure can contribute to behavioural problems, learning deficits, and lowered IQ in children.

To ensure compliance with lead standards, air quality is monitored through 36 three-month rolling averages. For an area to meet the lead National Ambient Air Quality Standard (NAAQS), no three-month rolling average in the previous 36 months may exceed 0.15 micrograms per cubic meter. The Clean Air Act, enforced by the EPA, plays a crucial role in regulating lead emissions and setting standards to protect public health and welfare.

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