Composition and structure of Atmosphere

Composition of the Atmosphere

The atmosphere is composed of gases, water vapour and dust particles. The proportion of the gases changes oxygen quantity to almost negligible at the height of 120km. carbon dioxide and water vapour are only found up to 90km

Gases

Carbon dioxide is meteorologically a very important gas as it is transparent to incoming solar radiation but opaque to the outgoing terrestrial radiation. It absorbs some part of radiation and reflects some part to the earth’s surface; it is largely responsible for greenhouse effect

Ozone is another important of the earth’s atmosphere found between 10 to 50km above the earth’s surface and acts as a filter to absorb ultra-violet rays.

Water Vapour

Water vapour is also a variable gas in the atmosphere, it decreases with an increase in altitude

In the warm and wet tropics, it may account for 4 percent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than 1 percent of the air.

Water vapour decreases once you move away from the equator and towards the polar region

It also absorbs the insolation of the sun and preserves the atmosphere’s heat

Dust particles

The Atmosphere has a sufficient capacity to keep small solid particles, which may originate from different sources and include salts, fine soil, smoke soot, ash, pollen, disintegrated particles from meteors

Dust particles are generally concentrated in the lower layers of the atmosphere; yet convectional air currents may transport them to great heights

The higher concentration of dust particles is found in subtropical and temperate regions

Structure of the Atmosphere

The Earth's atmosphere is divided into distinct layers, each with its own characteristics and functions. These layers, from the closest to the Earth's surface to the farthest, are:

1. Troposphere: This layer extends from the Earth's surface to an average altitude of about 8 to 15 kilometers (5 to 9 miles). It's where weather phenomena occur, and it contains approximately 75% of the atmosphere's mass. Temperature generally decreases with altitude in this layer.

2. Stratosphere: Above the troposphere lies the stratosphere, extending roughly from 15 to 50 kilometers (9 to 31 miles) above the Earth's surface. The stratosphere contains the ozone layer, which absorbs and filters out most of the sun's harmful ultraviolet (UV) radiation. In this layer, temperature increases with altitude due to the presence of ozone.

3. Mesosphere: Above the stratosphere lies the mesosphere, reaching approximately 50 to 85 kilometers (31 to 53 miles) in altitude. This layer protects the Earth from meteoroids, as they burn up upon entry due to the friction with air molecules. Temperatures decrease with altitude in the mesosphere.

4. Thermosphere: Extending from about 85 kilometers (53 miles) to about 600 kilometers (373 miles) above the Earth's surface, the thermosphere experiences extremely high temperatures due to the absorption of solar radiation. Despite the high temperatures, the thermosphere feels very cold because of its extremely low density. This is where the auroras occur and where satellites orbit.

5. Exosphere: The outermost layer of the atmosphere, starting at about 600 kilometers (373 miles) and gradually merging into outer space. The exosphere has an extremely low density of molecules and transitions into the vacuum of space.

Each layer of the atmosphere plays a crucial role in regulating temperature, protecting the Earth from harmful radiation, and enabling various atmospheric and celestial phenomena to occur

Salient Facts about Earth’s Atmosphere

Earth's atmosphere is a crucial component that sustains life on the planet. Here are some salient facts about it:

1. Composition: Primarily composed of nitrogen (78%), oxygen (21%), and trace amounts of other gases like argon, carbon dioxide, neon, helium, and more.

2. Layers: Divided into distinct layers based on temperature changes: troposphere (closest to the surface), stratosphere, mesosphere, thermosphere, and exosphere (farthest from Earth).

3. Troposphere: This layer is where weather occurs and where most of the mass of the atmosphere is concentrated. Temperature decreases with altitude in this layer.

4. Stratosphere: Contains the ozone layer, which absorbs harmful UV radiation. Temperature increases with altitude due to the presence of ozone.

5. Mesosphere: Protects the Earth from most meteoroids, where they burn up upon entering this layer due to friction with air molecules.

6. Thermosphere: Characterized by very high temperatures but with low density. It's where the auroras occur and where satellites orbit.

7. Exosphere: The outermost layer, where the atmosphere merges with outer space. The density of molecules is extremely low.

8. Greenhouse Effect: Certain gases like carbon dioxide, methane, and water vapor trap heat, contributing to the greenhouse effect. This phenomenon keeps the Earth's temperature within a range suitable for life but is currently a topic of concern due to human-induced climate change.

9. Air Pressure: Decreases with altitude. At sea level, the average air pressure is around 1013.25 millibars.

10. Importance for Life: Besides providing the air we breathe, the atmosphere protects us from harmful solar radiation, regulates the climate, and plays a crucial role in the water cycle.