Gases That Are Not Air Pollutants: What's Safe To Breathe?

Air is a mixture of gases, some of which are human-made and harmful to health and the environment. Air pollution is responsible for millions of premature deaths worldwide, with 99% of the global population breathing air with pollutant levels exceeding WHO guidelines. While the most abundant naturally occurring gas in the air, nitrogen (N2), is inert, other gases such as nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and ozone (O3) are harmful when present as pollutants. These gases can be released into the atmosphere through the combustion of fossil fuels, industrial activities, and vehicle emissions. Greenhouse gases, such as carbon dioxide (CO2) and methane (CH4), contribute to climate change, and while methane is not considered toxic, it is a potent greenhouse gas. Other gases, such as ammonia (NH3) and radon (Rn), can also have adverse effects on human health, with radon being the leading cause of lung cancer among non-smokers.

Nitrogen gas is inert in the atmosphere but essential for life on Earth

Nitrogen (N2) is the most abundant naturally occurring gas in the Earth's atmosphere, making up about 78% of the air we breathe. Despite its abundance, nitrogen gas in the atmosphere is relatively inert, doing very little. However, nitrogen plays a crucial role in the nitrogen cycle, which is essential for life on Earth.

The nitrogen cycle describes how nitrogen moves from the atmosphere to Earth, through soils and water, and back into the atmosphere. Nitrogen fixation is a key process in this cycle. Certain types of bacteria in soil and plant roots, such as legumes like soy, peas, and clover, convert nitrogen gas (N2) into ammonia (NH3). This process is essential because it makes nitrogen available to other organisms. Other bacteria then convert ammonia into nitrate (NO3-) and nitrite (NO2-), which can be used by plants and other bacteria.

Nitrogen is essential for plant growth and development. It is a key building block of DNA, which determines the genetics of all living things. Farmers can add nitrogen fertiliser to their crops to improve yields. However, too much nitrogen can be harmful, as it can be toxic to plants and animals and pollute aquatic systems.

Nitrogen levels can be affected by various human activities, such as the use of fertilisers in agriculture, and environmental phenomena. For example, the burning of fossil fuels releases nitrogen oxides (NOx) and nitrous oxide (N2O), a greenhouse gas, into the atmosphere. These emissions contribute to air pollution and the formation of acid rain, which can negatively impact natural and human-made environments.

In summary, while nitrogen gas in the atmosphere may be relatively inert, it is essential for sustaining life on Earth. Through the nitrogen cycle, nitrogen becomes available to living organisms, playing a crucial role in genetics, plant growth, and agriculture. Maintaining the right balance of nitrogen is vital for the health of our ecosystems and the environment.

Atmospheric oxygen is necessary for human and animal cellular respiration

Air is primarily composed of nitrogen (78%) and oxygen (21%), with trace amounts of other gases such as argon, carbon dioxide, neon, helium, methane, and more. While some gases are harmful air pollutants, oxygen is essential for human and animal life.

Oxygen, or O2, is a vital component of cellular respiration, which is the process by which cells release chemical energy to fuel their activity. This process occurs in both animal and plant cells, and it involves breaking down large molecules into smaller ones, producing energy in the form of adenosine triphosphate (ATP).

During cellular respiration, nutrients such as sugar, amino acids, and fatty acids are utilised. The most common oxidising agent in this process is molecular oxygen. When oxygen is present, aerobic respiration occurs, and the mitochondria undergo the Krebs cycle, producing carbon dioxide and water. This process is highly efficient, yielding up to 15 times more ATP than anaerobic metabolism.

If oxygen is absent, anaerobic cellular respiration or fermentation can occur, but these processes are less efficient in terms of energy production. In humans, the absence of oxygen during cellular respiration can lead to the production of lactic acid, resulting in muscle fatigue.

In summary, atmospheric oxygen is crucial for human and animal cellular respiration. It enables the production of energy in the form of ATP through the breakdown of nutrients. While other gases can be pollutants, oxygen plays a fundamental role in sustaining life on Earth.

Argon is the third most abundant gas in the atmosphere

The Earth's atmosphere is composed of various gases, both naturally occurring and human-made. The most abundant naturally occurring gas in the atmosphere is nitrogen (N2), making up about 78% of the air we breathe. Following closely behind is oxygen (O2), which accounts for approximately 21%.

Argon (Ar), an inert or noble gas, is the third most abundant gas in the Earth's atmosphere. It constitutes about 0.93% of the air. Despite its abundance, argon does not contribute to the greenhouse effect or global warming. This is primarily because argon is a monatomic gas, meaning it exists as single atoms rather than molecules. Its simple atomic structure prevents it from absorbing or emitting infrared radiation effectively, a key characteristic of greenhouse gases.

In contrast to argon, greenhouse gases possess the ability to absorb and emit infrared radiation, trapping heat within the Earth's atmosphere. This trapped heat leads to the greenhouse effect, resulting in warmer average temperatures and ultimately, global warming. Common examples of greenhouse gases include carbon dioxide (CO2), methane (CH4), and water vapor (H2O).

While argon is prevalent in the atmosphere, its chemical stability and inability to absorb or emit infrared radiation mean it plays a negligible role in global warming. Argon's inertness and stability also make it useful in various applications, such as lighting and cryogenics.

Additionally, it is important to note that while nitrogen gas constitutes the majority of the Earth's atmosphere, it does not actively contribute to the Earth's ecosystems. Nitrogen found elsewhere on Earth, outside of the atmosphere, is essential for life and plays a vital role in the nitrogen cycle.

Trace amounts of helium, neon, krypton, and hydrogen are found in the air

Air is a mixture of gases, most of which are naturally occurring. It also contains a significant amount of human-made air pollutants, including some that are unsafe to breathe and contribute to climate change. The dry composition of the atmosphere is mostly nitrogen and oxygen. It also contains fractional amounts of argon and carbon dioxide and trace amounts of other gases, such as helium, neon, methane, krypton, and hydrogen.

Nitrogen gas in the atmosphere does almost nothing, but nitrogen elsewhere on Earth is essential for life. Through the nitrogen cycle, nitrogen makes its way into the soil and water, binds with other elements, and is used by living things. Atmospheric chemistry in the troposphere is also influenced by human-made chemicals that can negatively impact human health and the environment. For example, vehicle exhaust contains nitrogen dioxide, as well as other polluting chemicals such as carbon monoxide and sulfur dioxide.

Oxygen from the atmosphere causes oxidation reactions that help break down matter and release nutrients into the soil, and is used by humans and animals in cellular respiration. Formaldehyde, benzene, and acetaldehyde are also human carcinogens found in vehicle emissions and wood burning.

While helium, neon, krypton, and hydrogen are found in trace amounts in the air, they are considered noble gases and are not known to be air pollutants. Noble gases are a group of elements that are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points. Their inertness or tendency not to react with other chemical substances is due to their electron configuration, specifically their full outer shell of valence electrons.

Radon is a radioactive gas that can cause lung cancer

Radon is a naturally occurring radioactive gas that is produced by the radioactive decay of uranium found in rocks and soils. It can also be found in water. Radon is invisible, odourless, and tasteless, making it difficult to detect without specialised equipment.

Radon is a known health hazard and is classified as a carcinogen by the Environmental Protection Agency (EPA). It is the second leading cause of lung cancer, responsible for about 21,000 lung cancer deaths every year. The risk of lung cancer increases by about 16% for every 100 Bq/m3 increase in long-term average radon concentration. Radon is estimated to cause between 3% to 14% of all lung cancers, depending on the national average radon level and smoking prevalence.

The link between radon and lung cancer has been well-established through studies in people and in laboratories. Radon gas, when inhaled, breaks down and releases radioactive particles that become lodged in the alveoli, the tiny air sacs in the lungs. These particles can also attach themselves to small dust particles and travel to the deep parts of the lungs. The energy released by these particles can damage lung cells, leading to cancer.

The risk of developing lung cancer from radon exposure is significantly higher for smokers, with smokers being 25 times more at risk than non-smokers. This is due to the synergistic effects of radon and cigarette smoking. However, radon is still the leading cause of lung cancer among non-smokers.

Radon levels are particularly high in indoor environments with poor ventilation, such as homes, schools, offices, mines, caves, and water treatment facilities. The EPA recommends that homes with radon levels at or above 4.0 pCi/L be mitigated to reduce the risk of radon exposure. Radon mitigation involves diverting radon gas from under the basement floor through a pipe to the outdoors.

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