7.1. COMPOSITION OF THE ATMOSPHERE

The atmosphere is composed of gases, water vapour and dust particles. The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.

The atmosphere is not just one type of gas; it contains a mixture of gases, water vapour, and dust. As we move higher into the atmosphere, the types and proportions of these components change. For instance, at 120 km above the Earth, the oxygen levels are so low that they become almost negligible. In contrast, gases like carbon dioxide and water vapour are mostly found within the first 90 km.

Think of the atmosphere like a layered cake. The bottom layers (closer to Earth) are rich in various ingredients (gases), while as you move upwards, the layers become thinner and less varied, resembling a frosting that barely covers the top.

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

Carbon dioxide (CO2) plays a critical role in Earth's climate. It allows sunlight to enter the atmosphere (transparent to solar radiation) but prevents some of the heat from escaping back into space (opaque to terrestrial radiation), which leads to warming of the Earth—this is known as the greenhouse effect.

Consider a car left in the sun. The glass lets sunlight in but keeps the heat trapped inside. Similarly, carbon dioxide lets warmth in from the sun while preventing some of it from escaping back into space, trapping heat and raising Earth's temperature.

Ozone is another important component of the atmosphere found between 10 and 50 km above the earth’s surface and acts as a filter and absorbs the ultra-violet rays radiating from the sun and prevents them from reaching the surface of the earth.

Ozone (O3) exists in the stratosphere and serves as a protective layer for life on Earth. It absorbs harmful ultraviolet (UV) radiation from the sun, preventing these rays from reaching the surface where they could cause serious damage to living organisms.

Imagine wearing sunscreen before going to the beach. Just like sunscreen protects your skin from harmful UV rays, ozone in the atmosphere acts like a natural sunscreen for the planet.

Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four per cent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air.

Water vapour varies significantly based on location. In tropical regions, it can make up as much as 4% of the atmosphere because of higher temperatures and humidity. Conversely, in deserts or polar regions, it may drop below 1% due to lower temperatures and lack of moisture.

Think about how a sponge holds water. In a humid environment (like a sponge soaked in water), there’s much more moisture in the air. In contrast, a dry environment (like a dry sponge) holds very little moisture, illustrating how water vapour behaves in different regions.

Atmosphere has a sufficient capacity to keep small solid particles, which may originate from different sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of meteors. Dust particles are generally concentrated in the lower layers of the atmosphere; yet, convectional air currents may transport them to great heights.

The atmosphere can carry various fine solid particles known as dust. These particles come from diverse sources including oceans (sea salts), land (soil), and even human activities (smoke). Most dust is found in the lower atmosphere, but strong air currents can lift them higher. These dust particles play a crucial role in weather patterns and cloud formation.

Picture a snow globe where small particles swirl around. Just as the particles in the globe can rise and fall, dust in the atmosphere is moved by winds, sometimes reaching high altitudes in the air.

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