The composition of air differs from place to place and is not constant across the globe. For example, in heavily polluted countries, the air has a higher percentage of carbon dioxide. Below are the major components of air: 

• Vaporized water
  The water in oceans and rivers evaporates and escapes into the atmosphere throughout the year. As a result, water vapor is one of the air’s constituents. It takes up a relatively tiny portion of the Earth’s atmosphere.
• Oxygen (O2)
  One of the essential elements of the air we breathe is oxygen. Have you ever attempted to light a candle without any air? You will find that it does not ignite in the absence of air. Combustion is aided by the presence of a substance present in the air. This substance is oxygen. Its presence is vital for life to sustain on Earth. The oxygen content of air is nearly 21%.
• Nitrogen
  You’ll find that if you blow on a burning torch, it goes out. Incombustible gases (gases that do not support combustion) are also present in the air. The presence of nitrogen plays a significant role in this. Nitrogen is the most common gas on Earth, responsible for about 78 percent of the atmosphere.
• CO2
  Carbon dioxide is generated mainly by the respiration of plants and animals and the combustion of gasoline. It takes up 0.038 percent of the atmosphere on the planet. Its occupancy changes from one spot to another depending upon pollution levels.
• Particles of soil and smoke
  Because of the combustion of fuels, our atmosphere also contains a certain percentage of smoke. It is a blend of gases that is hazardous. Apart from this, dust particles visible when a beam of light shines into a dim space are also present. Smoke and dust particles make up less than 1% of the atmosphere on Earth.

The term “air quality” refers to how pure or dirty the air is. Air quality is critical to monitor since contaminated air may be harmful to our health and the atmosphere. 

The Air Quality Index, or AQI, is used to assess air quality. The AQI is identical to a thermometer that varies from 0 to 500 degrees Fahrenheit. The AQI, on the other hand, instead of displaying increases in weather, shows changes in the volume of emissions in the environment.

Ozone is a layer of gas that forms a crust high in the Earth’s atmosphere. This layer is beneficial because it protects us from the sun’s ultraviolet rays. Ground-level ozone, on the other hand, is harmful to human beings. Ground-level ozone is created when sunlight causes chemical reactions between gasses such as nitrogen dioxide, carbon monoxide, and methane. These gases are released into the atmosphere from various sources, including manufacturing plants, automobile emissions, fuel vapors, etc. 

Particles and liquid droplets floating in the air are known as airborne objects. Construction facilities, smokestacks, vehicle exhaust pipes, explosions, volcanoes, and a variety of other causes release these particles into the environment. Chemical processes in the environment may also generate particles.

In this chapter, we learned about the basics of air and atmosphere. We gathered knowledge about air and its constituents. We learned about the factors that affect the quality of the air index.

1. What effect would air pressure have on the Earth’s atmosphere?
   Air pressure is generated as gravity pushes gas molecules in the atmosphere toward the Earth’s surface. The intensity by which air molecules push on a surface is measured by air pressure.
2. What are the five different layers of the atmospheres?
   The exosphere, thermosphere, mesosphere, stratosphere, and troposphere are the five primary layers of the Earth’s atmosphere. The layers start becoming thinner as we move away from the Earth’s surface before the atmosphere blends into the vacuum of outer space.
3. Which gases are the least abundant in the atmosphere?
   Pollutants, such as argon and carbon dioxide (CO₂), are found in extremely small concentrations.
4. The layer of the atmosphere is the hottest?
   Since the thermosphere contains a small number of molecules and atoms, even tiny quantities of solar radiation greatly raise air temperature, rendering it the hottest layer in the atmosphere.
5. What is the importance of the atmosphere?
   The presence of the atmosphere makes life possible on Earth. The gases present in the atmosphere are vital for photosynthesis and other life activities. The water cycle would be incomplete without the intervention of the atmosphere. It moderates the temperature of the Earth.