Earth's atmosphere

Earth's atmosphere is the layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

Density and mass

The density of air at sea level is about 1.2 kg/m3. Natural variations of the barometric pressure occur at any one altitude as a consequence of weather. This variation is relatively small for inhabited altitudes but much more pronounced in the outer atmosphere and space due to variable solar radiation

Related Topics:
Barometric pressure - Weather

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The atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used by meteorologists and space agencies to predict weather and orbital decay of satellites.

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The total mass of the atmosphere is about 5.1 × 1018 kg, or about 0.9 ppm of the Earth's total mass.

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The above composition percentages are done by volume. Assuming that the gases act like ideal gases, we can add the percentages p multiplied by their molar masses m, to get a total t = sum (p·m). Any element's percent by mass is then p·m/t. When we do this to the above percentages, we get that, by mass, the composition of the atmosphere is 75.523% N2, 23.133% O2, 1.288% Ar, 0.053% CO2, 0.001267% Ne, 0.00029% CH4, 0.00033% Kr, 0.000724% He, and 0.0000038 % H2.

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This graph is from the NRLMSISE-00 atmosphere model, which has as inputs: latitude, longitude, date, time of day, altitude, solar flux, and the earth's magnetic field daily index.

Related Topics:
NRLMSISE-00 - Model

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