7.2. Gases

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 surrounding us is made up of various components, primarily different gases, but also includes water vapour and dust particles. As we move higher into the atmosphere, the proportion of these gases changes. At a height of 120 km, the oxygen levels become very low, while carbon dioxide and water vapour diminish at around 90 km. This indicates that the atmosphere is not uniform, and its composition varies significantly with altitude.

Think of the atmosphere like a layered cake, where each layer has a different flavor. The lower layers have plenty of oxygen (the flavor most familiar to us), but as you go higher, the flavors (like oxygen and carbon dioxide) become less pronounced, showing how composition varies at different heights.

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. 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.

Carbon dioxide (CO2) plays a crucial role in regulating the Earth's temperature. It allows sunlight to enter the atmosphere but traps some of the heat that the Earth radiates back into space, which keeps our planet warm—a phenomenon known as the greenhouse effect. Ozone (O3), found in the stratosphere, serves an essential function by absorbing harmful ultraviolet (UV) rays from the Sun, protecting living organisms from potential damage caused by these rays.

Imagine carbon dioxide as a warm blanket that helps keep our planet cozy at night by trapping heat, while ozone acts like sunscreen that prevents harmful UV rays from burning our skin. Without these features, the Earth would be inhospitable for life as we know it.

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 also decreases from the equator towards the poles. It also absorbs parts of the insolation from the sun and preserves the earth’s radiated heat. It thus, acts like a blanket allowing the earth neither to become too cold nor too hot.

Water vapour plays a significant role in the atmosphere and varies widely in concentration, being highest in tropical regions and minimal in polar regions. This gas not only helps regulate temperature by holding heat but also facilitates natural weather processes such as the formation of clouds. It essentially helps to maintain a balance in Earth’s climate, preventing extremes in temperature.

You can think of water vapour like the thermostat in a house. It helps keep the temperature comfortable, similar to how a thermostat regulates the heat in a building. In places where there's a lot of moisture, the 'thermostat' is set to keep things warm, while in arid areas, it's turned down, leading to colder temperatures.

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 is not just a mix of gases; it also contains tiny solid particles known as dust. These particles originate from various sources, such as sea spray, soil, and even meteor debris. While most of these particles stay close to the Earth's surface, strong upward air movements can carry them higher into the atmosphere.

Imagine a snow globe filled with glitter. When you shake it, the glitter (dust particles) swirls around inside. Similarly, dust particles are normally found closer to the ground but can be lifted and dispersed throughout the atmosphere, especially when wind currents are strong.

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