Air Pollutants: Indoor And Outdoor Threats

There are many pollutants that can be found both indoors and outdoors, including volatile organic compounds (VOCs), carbon monoxide, and nitrous oxide (NO2). These pollutants can have a significant impact on human health, causing issues such as eye and throat inflammation, severe migraines, and even cancer in the case of long-term exposure. While outdoor air pollution is regulated under the Clean Air Act in the United States, indoor air pollution is less well-characterised and not subject to the same regulations. However, modulating indoor pollutant sources can reduce both indoor and outdoor pollutant concentrations, improving public health in both environments.

Nitrous oxide (HONO)

Nitrous acid (HONO) is a common indoor pollutant, which is produced by the reaction of NO2 with water. It is a strong oxidant and can be found in both indoor and outdoor environments. HONO is a major source of indoor OH radicals, which can have adverse health effects. It has an average indoor concentration of 5-10 ppb, but this can be elevated to up to 90 ppb through combustion when using gas stoves, space heaters, and open fireplaces.

HONO is also a significant outdoor pollutant, particularly in urban areas. It is a major precursor of hydroxyl (OH) radicals, which initiate tropospheric chemistry leading to the formation of secondary pollutants. Sources of atmospheric HONO are not fully understood, but it is known that nitric acid (HNO3) formed from photooxidation of NO2 can be converted into HONO with a yield of ~53%. Dark NO oxidation by NO3 radicals in the presence of H2O also produces HONO, but with a lower yield of 2%.

HONO plays a crucial role in atmospheric oxidation capacity and thus regional air quality and global climate change. However, due to its chemically reactive species and low concentrations, measurement of HONO is challenging. As a result, the sources and sinks of HONO, as well as their formation mechanism in the atmosphere, are still not completely defined and understood.

There is great interest in understanding indoor HONO chemistry and the factors controlling it, as it can give rise to health risks due to its toxicity, acidity, aqueous solubility, and high reactivity. HONO can produce carcinogenic molecules such as nitrosamines, known as third-hand smoke, through reaction with surface-deposited nicotine and organic amines.

Volatile organic compounds (VOCs)

VOCs are a concern not only because of their potential health effects but also because they can accumulate inside buildings, leading to high concentrations of toxic gases. While toxic gases are rare to find indoors, they still pose a significant danger.

The concentration of VOCs in the air is influenced by both indoor and outdoor sources. For example, outdoor levels of VOCs can be influenced by combustion or local traffic sources, which can then impact indoor levels.

It is important to note that modulating indoor sources of VOCs can help reduce both indoor and outdoor exposures. This can be achieved through proper ventilation and the use of low-emission products.

Overall, VOCs are a significant contributor to air pollution and can have serious health consequences. It is important to be aware of the potential sources of VOCs and take steps to reduce exposure to these harmful compounds.

Carbon monoxide

Indoors, carbon monoxide can be produced by the use of heating appliances, such as furnaces, boilers, and water heaters. It can also be produced by cooking on gas stoves or using charcoal grills indoors. Additionally, the use of generators, pressure washers, and other fuel-powered equipment in enclosed spaces can lead to carbon monoxide poisoning.

The effects of carbon monoxide poisoning can be severe and even life-threatening. When carbon monoxide is inhaled, it binds to red blood cells, preventing them from carrying oxygen throughout the body. This can lead to symptoms such as headaches, dizziness, weakness, nausea, and confusion. In severe cases, carbon monoxide poisoning can cause loss of consciousness, brain damage, and even death.

It is important to take steps to prevent carbon monoxide poisoning, especially in indoor spaces. This includes ensuring proper ventilation, regular maintenance of fuel-burning appliances, and the installation of carbon monoxide detectors. Carbon monoxide detectors should be placed near sleeping areas and at every level of the home, and their batteries should be checked regularly.

Additionally, it is important to be aware of the signs of carbon monoxide poisoning and to seek fresh air and medical attention if symptoms occur. In cases of suspected carbon monoxide poisoning, it is crucial to leave the area immediately and call for help. By taking these precautions, the risks associated with carbon monoxide exposure can be significantly reduced.

Natural gases

Natural gas is a fossil fuel that is primarily made up of methane. It is formed from the remains of dead plants and animals that have been exposed to extreme heat and pressure over millions of years. This process, known as fossilisation, results in the creation of natural gas deposits that are often found deep underground. Natural gas is widely used as a source of energy for heating, cooking, and electricity generation. It is considered a cleaner alternative to other fossil fuels, such as coal and oil, due to its lower carbon emissions.

One of the main sources of indoor natural gas pollution is from heating appliances. When natural gas is burned for heating or cooking, it can release harmful pollutants, including nitrogen oxides and carbon monoxide. These pollutants can build up indoors, particularly in poorly ventilated areas, and pose a risk to human health. Carbon monoxide, for example, is a toxic gas that can cause headaches, dizziness, and even death in high concentrations.

Outdoor sources of natural gas pollution include leaks from pipelines and storage facilities, as well as emissions from industrial processes and power plants that utilise natural gas. While natural gas is often considered a cleaner alternative to other fossil fuels, unburned methane released during extraction, transmission, and distribution can contribute to global warming. Methane is a potent greenhouse gas that traps heat in the Earth's atmosphere, contributing to climate change.

To mitigate the risks associated with natural gas pollution, it is important to ensure proper ventilation in indoor spaces and to regularly maintain heating and cooking appliances. Additionally, transitioning to renewable energy sources, such as solar and wind power, can help reduce our reliance on natural gas and minimise its environmental impact. By implementing measures to control and reduce natural gas pollution, we can improve air quality and protect both human health and the environment.

Asbestos

Friable asbestos has been found in about 20% of public buildings. Asbestos fibres can be released into the air in homes when asbestos-containing materials are disturbed by cutting, sanding or other remodelling activities. This can increase asbestos levels and endanger people living in those homes. Therefore, it is important to take the proper precautions when handling asbestos to avoid risking your health and the health of others.

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