Density and mass

Density and mass

The average mass of the atmosphere is about 5 quadrillion (5×10¹⁵) or 1/1,200,000 the mass of Earth. According to the"The total mean mass of the atmosphere is 5.1480×10¹⁸ kg with an annual range due to water vapor of 1.2 or 1.5×10¹⁵ kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27×10¹⁶ kg and the dry air mass as 5.1352 ±0.0003×10¹⁸ kg."

The density of air at sea level is about 1.2  kg/m³ (1.2 g/L). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the . Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the  More sophisticated models are used to predict orbital decay of satellites.