Air Pollutants: Understanding The Invisible Danger Around Us

Air pollutants are contaminants that can cause serious long-term effects on human health, including cancer and respiratory diseases. These pollutants can be categorised as either criteria pollutants or hazardous air pollutants (HAPs), also known as air toxics. Criteria pollutants, such as particle pollution, ground-level ozone, carbon monoxide, and nitrogen oxides, are used to assess whether a region meets air quality standards. On the other hand, HAPs are chemical compounds that are known or suspected to cause cancer and other adverse health effects. These pollutants are generally more localised and originate from human-made sources such as vehicles, factories, and power plants. Exposure to air pollutants can lead to a range of respiratory issues, especially in vulnerable populations like infants, older adults, and people with pre-existing lung conditions.

Hazardous air pollutants (HAPs)

HAPs include a range of substances such as benzene, perchloroethylene, methylene chloride, dioxins, asbestos, toluene, and metals like cadmium, mercury, chromium, and lead compounds. Many of these pollutants are known to accumulate in the body over time, even at low levels of exposure, and can lead to long-term health issues. For example, asbestos exposure has been linked to mesothelioma, lung cancer, and asbestosis. Similarly, benzene, a component of gasoline, is another well-known HAP associated with adverse health effects, including cancer and reproductive issues.

The Clean Air Act, enacted in 1990, originally identified 189 HAPs for regulation. Since then, the list has been modified through rulemaking, with pollutants being added or delisted based on emerging scientific evidence and changing environmental conditions. As of 2022, there are 188 federally regulated HAPs in the United States. The Environmental Protection Agency (EPA) is tasked with regulating these hazardous air pollutants and reducing their emissions to protect public health and the environment.

To achieve this goal, the EPA employs various strategies, including developing regulatory programs, setting national emission standards, and conducting inspections of facilities to ensure compliance with the established standards. These standards, known as Maximum Achievable Control Technology (MACT) standards and Generally Achievable Control Technology (GACT) standards, aim to minimize HAP emissions from industrial and area sources, such as paper mills and fuel combustion sources. The EPA also collaborates with state, local, and tribal governments to address HAPs more effectively and protect communities across the country from the detrimental effects of these toxic pollutants.

Respiratory diseases caused by air pollutants

Air pollutants are chemical compounds that are known or suspected to cause cancer and other serious health issues, including respiratory diseases. These respiratory diseases caused by air pollutants can be acute or chronic.

Acute respiratory diseases range from mild irritations, inflammation, and allergic reactions to impaired lung function and even complete respiratory failure, depending on the level of exposure to the air pollutant.

Chronic respiratory diseases caused by air pollutants include chronic obstructive pulmonary diseases (COPD), cardiovascular diseases, asthma, and lung cancer. COPD is a lung disease primarily characterised by an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. It is a major cause of disability and is the third-leading cause of death in the United States. Tobacco smoke has been identified as a key factor in the development and progression of COPD. Women in developing countries are at a high risk of developing COPD due to exposure to household wood smoke from cooking.

Asthma is another respiratory disease that can be caused or aggravated by air pollutants. Environmental factors such as exercise, humidity, temperature, allergens, viral infection, stress, and inhalation of air pollutants can trigger asthma symptoms. Children with asthma are more affected by particle pollution than adults with asthma, possibly due to behavioural factors such as increased time spent outdoors and exercising. Poor inner-city children with asthma may be at increased risk from air pollution due to their proximity to high-density traffic or industrial sources of particle pollution, as well as poor indoor air quality.

Additionally, air pollutants have been linked to long-term effects, including mesothelioma, lung cancer, and asbestosis. For instance, asbestos and other fibres have been associated with these respiratory issues. Furthermore, exposure to elevated concentrations of ground-level ozone is particularly harmful to people with asthma or lung disease, and children are more likely to be affected due to their higher prevalence of asthma.

Prenatal and perinatal exposure to air pollutants is also a critical concern, as it can lead to adverse birth outcomes such as preterm birth, lower birth weight, and lung developmental defects, which can further associate with respiratory diseases later in life.

Common air pollutants

Air pollutants are classified as either "criteria pollutants" or "hazardous air pollutants" (HAPs). Criteria pollutants are used to determine whether a region meets air quality standards, whereas HAPs are chemical compounds suspected of causing cancer and other serious health and environmental issues.

The Clean Air Act regulates six common air pollutants: particle pollution (particulate matter), ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants are microscopic solids or liquid droplets that can be inhaled and cause a range of respiratory issues. Fine particulate matter, or PM2.5, refers to particles with diameters of 2.5 micrometres or less. These particles are so small that they can bypass the body's defences and lodge in the lungs, causing scarring and reduced lung function. They may also enter the bloodstream, contributing to heart disease and impacting organs and the nervous system.

Particulate matter is generated by combustion in motor vehicles, power plants, wood burning, industrial processes, and fires. It can also come from natural sources such as dust from coal or silica-containing rocks, causing pneumoconiosis (black lung disease) and silicosis, respectively. Another source of particulate matter is textile fibres, which can lead to byssinosis (brown lung disease).

Ground-level ozone is harmful to people with asthma or lung disease, and children are particularly vulnerable. Carbon monoxide, a toxic gas, is produced by the combustion of fossil fuels and has serious health effects, especially for infants whose lungs are still developing. Sulfur oxides and nitrogen oxides are produced by industrial processes and contribute to respiratory issues and environmental problems such as acid rain.

Lead is a toxic metal that was historically used in products like paint and gasoline. While lead has been largely removed from gasoline, it is still used in aviation fuel and some manufactured products. Exposure to lead can cause serious health issues, especially in children whose brains and nervous systems are more susceptible to the toxic effects.

Air pollutants in the home

One of the key challenges in controlling IAP is identifying the sources of pollution and their emission rates, which can vary significantly. Developing monitoring systems to measure indoor pollutant concentrations is crucial for effective control and improvement of indoor air quality (IAQ). This includes the use of novel materials-based sensors, smart monitoring systems, and smart home technologies.

Some common indoor air pollutants include tobacco smoke, which is a significant contributor to the development of chronic obstructive pulmonary disease (COPD). Other pollutants include ozone, sulfur oxides, carbon monoxide, nitrogen oxides, and particulate matter (PM). PM, in particular, has been associated with cancer, and exposure to elevated levels of ground-level ozone can aggravate asthma and cause long-term breathing problems, especially in children.

To mitigate the impact of indoor air pollutants, it is important to enhance ventilation, reduce emissions at the source, and utilize air purification systems. Smart home technologies offer promising solutions by providing remote control of ventilation systems, appliances, and blinds, contributing to improved IAQ and reduced energy costs. Additionally, the development of sensitive gas detection technologies, such as the smart E-nose system, enables high-performance monitoring of indoor air quality in real time.

Air toxics

Hazardous air pollutants, also known as air toxics, are chemical compounds suspected or known to cause cancer, birth defects, and other serious health issues. They can be gases, such as hydrogen chloride, benzene, and toluene, or compounds and metals such as asbestos, cadmium, mercury, and chromium. The US Environmental Protection Agency (EPA) has classified 188 pollutants as hazardous, including 33 that are considered the greatest threat to public health in urban areas.

Major sources of outdoor air toxics include emissions from coal-fired power plants, industries, refineries, and vehicles. Certain industries produce specific toxins, such as ethylene oxide leaks from medical equipment sterilization facilities. Chemical releases from accidents at industrial facilities or during hazardous material transportation can also result in air toxic releases. Indoor air can also contain hazardous pollutants from tobacco smoke, building materials (e.g., asbestos), and consumer products like cleaning supplies and air fresheners.

The EPA has been working to reduce emissions of air toxics since the passage of the Clean Air Act Amendments in 1990. They use hazardous air pollutant emissions and ambient monitoring data to develop regulatory programs that limit emissions from stationary sources. The Air Toxics Screening Assessment (AirToxScreen) is an EPA tool that provides communities with information about health risks from air toxics, helping local and tribal agencies, and the public identify existing and emerging issues.

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