Composition of Air and Its Uses

Three-fourths of all air resides in the troposphere, the lowest layer of the Earth’s atmosphere. Air is a mixture of gases, most of which are naturally occurring. Air also contains a significant amount of human-made air pollutants, including some that are not safe to breathe and some that warm our planet’s climate. The troposphere also contains water in all three phases (liquid, solid, and gas) as well as solid particles called aerosols.

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.

​What's in the Air?

Match

Match the following gases with their percentages in the atmosphere.

• Nitrogen

• Oxygen

• Carbon Dioxide

• Argon

78%

21%

0.04%

0.96%

• 78%

• 21%

• 0.04%

• 0.96%

Gases

The most abundant naturally occurring gas is nitrogen (N₂), which makes up about 78% of air. Oxygen (O₂) is the second most abundant gas at about 21%. The inert gas argon (Ar) is the third most abundant gas at 0.93%. There are also trace amounts of carbon dioxide (CO₂), neon (Ne), helium (He), methane (CH₄), krypton (Kr), hydrogen (H₂), nitrous oxide (NO), xenon (Xe), ozone (O₃), iodine (I₂), carbon monoxide (CO), and ammonia (NH₃) in the atmosphere.

Multiple Choice

What is the third most abundant gas in the atmosphere?

• Nitrogen

• Oxygen

• Argon

• Carbon Dioxide

Water Vapor

Due to the water cycle, the amount of water in the air is constantly changing. The lower troposphere can contain up to 4% water vapor (H₂O) in areas near the tropics, while the poles contain only trace amounts of water vapor. The concentration of water vapor decreases drastically with altitude. The upper troposphere has less water vapor than air near the surface, the stratosphere and mesosphere have almost no water vapor, and the thermosphere contains none at all.

Multiple Choice

How much water vapor is in the highest layer, the thermosphere?

• None

• A very large amount

• A very small amount

Aerosols

Air also contains tiny solid particles called aerosols, such as dust, sea salt, and ash from erupting volcanoes or forest fires. Many of these particles are so small that they are microscopic. Others are large enough to see. Aerosols affect climate by helping clouds form and shading the planet by scattering or absorbing sunlight. In the last century, manufacturing and widespread use of combustion engines have increased the number of aerosols in the atmosphere as particulate matter spews from smokestacks and exhaust pipes. Burning wood and other materials also add particles to the air.

Like everything on Earth, the air is made of chemicals. The chemicals in the air often combine with each other, or with other chemicals from the Earth’s surface, through chemical reactions. Many of these chemical reactions help maintain healthy natural environments and are vital for plants and animals. 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 soil and water, binds with other elements, and can be used by living things. Oxygen from the atmosphere causes oxidation reactions that help break down matter and release nutrients into soils, and is used by humans and animals in cellular respiration.

​Atmospheric Chemistry

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. Nitrogen dioxide reacts with atmospheric oxygen to form tropospheric ozone which is hazardous to plant and animal cells.

• Smog, which is mainly made of ozone and particulate carbon (soot) emitted by coal-burning power plants, causes damage to the lungs of humans and animals.

• Factories that burn fossil fuels also release sulfur and nitrogen dioxides, which combine with water in the atmosphere to make acid rain. Acid rain causes damage to natural and human-made environments.

​Atmospheric Chemistry continuted...

Chemistry of the Air

Multiple Choice

Which type of ozone is important for protecting humans?

• The ozone that is human made

• The ozone that occurs naturally in the stratosphere

Multiple Choice

Is water vapor a greenhouse gas?

• Yes

• No