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, 100 km is usually used as the border to space. The lowest layer of the atmosphere is called the troposphere and contains almost all water vapor 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 means of radiation and convection. It is in this layer where we humans live, breathe, work and fly.
The composition of the atmosphere is important for sustainable life on this planet. In the lower part we find most of the weather creating circumstances so that life as we know it can prosper on this planet. This is a natural effect and its largely self regulating combined with the day/night exposure to the sun due to the rotation of our planet.
These pages can only paint a superficial picture of a very interesting topic, as not everything is fully understood by science. Because our atmosphere is so chaotic, I wonder if we will ever be able to predict weather phenomena with 100% certainty.
The atmosphere consists of the following chemical elements (2022):
| Element | Amount % | Amount ppm |
| Nitrogen (N2) | 78.08 | 780800 |
| Oxygen (O2) | 20.95 | 209500 |
| Water (H2O) | 0 - 4 | 0 - 40000 |
| Trace gases (< 1%) | ||
| Argon (AR) | 0.93 | 9300 |
| Carbon Dioxide (CO2) | 0.0415 | 415 |
| Neon (NE) | 0.0018 | 18 |
| Helium (HE) | 0.0005 | 5 |
| Methane (CH4) | 0.00017 | 1.7 |
| Hydrogen (H2) | 0.00005 | 0.5 |
| Nitrous Oxide (N2O) | 0.00005 | 0.5 |
| Nitrogen Dioxide (NO2) | 0.000002 | 0.02 |
| Ozone (O3) | 0,000004 | 0,04 |
Some minute amounts of Krypton, Iodine, Xenon and Radon are also found in our atmosphere. Click these links for agraphical overviewandtotal atmospherewhich gives you more insight into the amounts related to each element and the total atmosphere.
The most common (after nitrogen and oxygen) gases are, in order of importance: water vapour, carbon dioxide and methane. Since 1750, levels of these gases have increased by: 150% for methane and 35% for carbon dioxide (source: http://www.physicalgeography.net). After 1998, these increases slowed down considerably.
But to assess the effect of these gases we need to take a look at the absorption of each of them at the molecule level. See image to the right. As it turns out that, for example methane (CH4) is totally masked by water vapor!
Source (image too):WUWT article, Methane: The Irrelevant Greenhouse Gas.
About half of these gases are below 5000 ft and 75% is below 11000 ft. Standard sea level pressure is 760 mm/Hg (1013,25 hPa / 29.92 inHg), at 18000 ft it is 380 mm/Hg (50% or 507 hPa / 14.97 inHg) and at 34000 ft it is 190 mm/Hg (25% or 253 hPa / 7.47 inHg).
In terms of volume, its composition remains virtually the same until an altitude of 75 km (246,000 ft) is reached. Variations are also found in the amount of water vapour, ozone and carbon dioxide.
The amount of non-gaseous material can also vary greatly depending on the location. Volcanic ash, dust and fine sand (think deserts like: Sahara, Gobi) can travel hundreds of miles across continents. When it rains, you can see it on the surface of windows, cars, etc.
As mentioned above, the atmosphere also contains some fine solid particles such as soot (from fires and fuel combustion), dust, sand, salt and volcanic eruptions/ash. These can have a short-term (~3 years) effect on temperature, as they can block incoming radiation and contribute to the condensation processes that form clouds and fog at the lower levels. If this creates fog, it is called smog.
Our next page dives into the details of the various chemicals in the atmosphere.
Written by EAI.
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