Earths Atmosphere, I

The vertical extend of the atmosphere is difficult to define, it surrounds the earth and becomes increasingly thinner until at some point space is reached. The lowest layer of the atmosphere is called the troposphere and contains almost all water vapour and approximately 75% of all molecular mass of the atmosphere, its height varies from 18 km at the equator to 8 km at the poles.

The sun warms the air or atmosphere indirectly, the earth receives the solar radiation (insolation) and heats the lower layers of the atmosphere by radiation and convection. It is in this layer where we humans live, breathe and fly.

The composition of the atmosphere is important for sustainable life on this planet. It makes sure that enough solar heat remains trapped so that life can prosper.

Composition

The atmosphere consists of 78,08% Nitrogen (N₂), 20,95% Oxygen (O₂) and the rest includes 0-4% Water (H₂O), 0,93% Argon (A_R), 0,039% Carbon Dioxide (CO₂), 0,0018% Neon (N_E), 0,0005% Helium (H_E), 0,00017% Methane (CH₄), 0,00005% Hydrogen (H₂), 0,00003% Nitrous Oxide (N₂O) and 0,000004% Ozone (O₃). Some traces of Krypton, Xenon and Radone are also found in the atmosphere.

The most effective greenhouse gases are (in order of importance): Water, Methane and Carbon Dioxide. Since 1750 the levels of these gases have increased by: 150% for Methane and 35% Carbon Dioxide (source: HTTP://www.physicalgeography.net).

About half of these gases are below 5000 ft and 75% is below 11000 ft. Standard sea level pressure is 760mm/Hg, at 18000 ft it is 380 mm/Hg (50%) and at 34000 ft it is 190 mm/Hg (25%). By volume this composition stays almost the same until a height of 75km is reached. Variations are also found in the amount of water vapor, ozone and carbon dioxide.

The amount of non gaseous matter can also vary widely, depending on the location. Volcanic ashes, dust and fine sand (Sahara) can travel hundred of miles and across continents.

Water (H₂O)

Found as vapor in the atmosphere below about 20000 ft, reaching levels from zero (poles) to 4% (tropical). Although small in quantity but its effect on weather can be dramatic. When water changes state from vapor to visible (water or ice) produces clouds, rain, fog and other phenomena it has a profound effect on temperature and humidity. Water vapor has its source from oceans, lakes, rivers, forest and plant respiration.

Ozone (O₃)

Formed in the upper levels of the stratosphere and the lower levels of the mesosphere by the sun and blocks dangerous UV radiation which kills life as we know it on earth. Consists of three oxygen molecules. The amount of ozone depends on the season, amount of solar radiation and certain human produced chemicals, which are banned these days.

Carbon dioxide (CO₂)

A colorless, heavy gas with no smell. Produced by oxidation processes in human (1 kg per day) and animal life (breathing), decomposing processes in the sea and the burning of fuels, wood and other materials containing carbon molecules. This molecule consists of 13 parts of carbon and 32 parts of oxygen by weight.

Large amounts of carbon dioxide are dissolved in the oceans, plant life is also a major remover of CO₂. Off all the CO₂ emitted in the atmosphere (0,039% / 390ppm) only 3% is of human origin (0,00117% / 11,7ppm). Worldwide aviation emissions causes only 2% of all man made carbon in the atmosphere (0,0000234% / 0,234ppm).

To learn more about carbon dioxide (CO₂) and its real effect on our atmosphere, follow this link to CO₂ Science. A higher CO₂ level encourages growth in plant life and is eventually converted into oxygen needed for humans. It is an essential gas for life on this planet and not a pollutant. Without CO₂ there would be no life possible as we know it. Read more about the carbon cycle on our planet.

Solid particles

As said above, the atmosphere also contains an amount of fine solid particles as soot (from fires and burning of fuel) dust, sand, salt and volcanic ashes. These do have an effect on the temperature as they can block incoming radiation and contribute to the condensation processes which forms clouds and fog in the lower levels. If fog is formed because of this then it is called smog.