What is the Percentage of Nitrogen in Air?
Earth’s atmosphere is a complex mixture of gases, but nitrogen overwhelmingly dominates. It makes up roughly 78% of the air we breathe (by volume), making it the most abundant gas in the Earth’s atmosphere.
The Composition of Air: More Than Just Nitrogen
While nitrogen holds the lion’s share, it’s crucial to understand the other components that contribute to the air’s overall composition. While a precise number can fluctuate slightly depending on location and altitude, a standard approximation for dry air composition is:
- Nitrogen (N2): approximately 78%
- Oxygen (O2): approximately 21%
- Argon (Ar): approximately 0.9%
- Other Gases (Carbon Dioxide, Neon, Helium, Methane, etc.): Trace amounts, making up less than 0.1% combined.
Importantly, this breakdown refers to dry air, meaning air without water vapor. The percentage of water vapor in the air can vary significantly depending on weather conditions and geographic location, ranging from almost zero in very dry climates to as much as 4% in humid tropical regions. These fluctuations can slightly alter the percentage compositions of the other gases.
Sources and Stability
The relatively constant proportion of nitrogen in the air, unlike other gases like carbon dioxide that fluctuate due to human activity, is maintained through a complex nitrogen cycle. This cycle involves biological and geological processes that constantly fix, release, and recycle nitrogen within the Earth’s system. Volcanic activity, decomposition of organic matter, and lightning strikes all contribute to the release of nitrogen gas into the atmosphere. Conversely, nitrogen-fixing bacteria in the soil and oceans convert atmospheric nitrogen into usable forms for plants and other organisms, removing it from the atmosphere.
Nitrogen: An Inert Gas with Vital Roles
Despite its prevalence, nitrogen in its gaseous diatomic form (N2) is relatively inert. This inertness is due to the strong triple bond between the two nitrogen atoms, making it difficult to break apart and react with other elements. However, this very characteristic makes it a useful buffer gas, diluting the highly reactive oxygen and preventing rapid oxidation (combustion) that could lead to runaway fires.
Biological Significance
While elemental nitrogen is inert, nitrogen in its reactive forms is essential for life. Plants absorb nitrogen from the soil in the form of nitrates and ammonia, which they use to build proteins, nucleic acids (DNA and RNA), and other vital organic molecules. Animals obtain nitrogen by consuming plants or other animals. Nitrogen is therefore a fundamental building block of all living organisms.
Industrial Applications
Beyond its natural roles, nitrogen has numerous industrial applications. Liquid nitrogen (LN2), formed by cooling gaseous nitrogen to extremely low temperatures, is used as a cryogenic coolant for preserving biological samples, cooling electronics, and in various industrial processes. Gaseous nitrogen is used to create inert atmospheres in food packaging, electronics manufacturing, and other applications where oxidation is undesirable. Nitrogen is also a key component in the production of fertilizers, ammonia, and various other chemicals.
Frequently Asked Questions (FAQs) About Nitrogen in the Air
Here are some frequently asked questions to provide a more comprehensive understanding of nitrogen in the air:
FAQ 1: Does the percentage of nitrogen in the air change with altitude?
Yes, but not dramatically within the lower atmosphere. While the proportion of gases remains relatively constant up to a certain altitude (homosphere), the overall density of the air decreases with altitude. This means there are fewer molecules of all gases, including nitrogen, at higher altitudes. Above the homosphere, in the heterosphere, the composition starts to change as lighter gases like hydrogen and helium become more abundant.
FAQ 2: Why is nitrogen in the air so important?
Nitrogen plays several crucial roles. As a buffer gas, it dilutes oxygen and prevents uncontrolled combustion. It’s a building block for proteins and DNA, essential for all life forms. It’s also vital for agriculture, serving as a primary component of fertilizers that support crop growth.
FAQ 3: What is nitrogen fixation?
Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into forms that plants can use, such as ammonia (NH3) or nitrates (NO3–). This process is primarily carried out by certain bacteria and archaea, either freely living in the soil or in symbiotic relationships with plants.
FAQ 4: Is too much nitrogen in the air a problem?
No, having a high concentration of nitrogen itself isn’t directly harmful. However, the issue arises when reactive nitrogen compounds, such as nitrogen oxides (NOx), are released into the atmosphere. These compounds are pollutants that contribute to smog, acid rain, and respiratory problems.
FAQ 5: What are some uses of nitrogen besides agriculture?
Besides fertilizer production, nitrogen is used in the cryogenic cooling of various materials, as a blanketing agent in chemical and electronic industries to prevent oxidation, in the production of explosives, and as a propellant in some aerosol products.
FAQ 6: How does water vapor affect the percentage of nitrogen in the air?
Water vapor displaces other gases in the air. Because the total percentage must add up to 100%, an increase in water vapor will result in a slight decrease in the percentages of other gases, including nitrogen, oxygen, and argon.
FAQ 7: What is the difference between nitrogen and nitrogen gas?
These terms are often used interchangeably. However, technically, nitrogen refers to the element itself (N), while nitrogen gas refers to the diatomic molecule (N2) that makes up the majority of nitrogen in the air.
FAQ 8: How is nitrogen extracted from the air for industrial use?
Nitrogen is typically extracted from the air using a process called fractional distillation of liquid air. Air is first cooled to extremely low temperatures, causing it to liquefy. Then, the liquid air is slowly warmed, and the different gases are separated based on their boiling points. Nitrogen, with a lower boiling point than oxygen, boils off first and is collected.
FAQ 9: What happens if you breathe pure nitrogen?
Breathing pure nitrogen would be deadly because it would displace oxygen, leading to asphyxiation. Oxygen is essential for cellular respiration, and without it, the body’s cells cannot function.
FAQ 10: Does the percentage of nitrogen in the air vary significantly around the world?
No, the percentage of nitrogen remains relatively consistent globally. Local variations in air composition are primarily due to changes in humidity (water vapor content) and levels of pollutants near industrial areas. The large reservoir of atmospheric nitrogen keeps the overall concentration relatively stable.
FAQ 11: Is nitrogen in the air a greenhouse gas?
No, nitrogen gas (N2) is not a greenhouse gas. Greenhouse gases absorb and trap heat in the atmosphere, contributing to global warming. Nitrogen molecules do not absorb infrared radiation in a way that traps heat.
FAQ 12: What is the future of nitrogen levels in the atmosphere?
While the total amount of nitrogen in the atmosphere is vast and relatively stable, the reactive forms of nitrogen are a growing concern. Increased fertilizer use and industrial processes are leading to higher levels of nitrogen oxides and other reactive nitrogen compounds in the environment, which can have significant impacts on air and water quality. Managing these reactive nitrogen compounds is crucial for mitigating environmental problems.