Density of air

The density of air or atmospheric density, denoted ρ, is the mass per unit volume of Earth's atmosphere at a given point and time. Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmospheric pressure, temperature, and humidity. According to the ISO International Standard Atmosphere (ISA), the standard sea level density of air at 101.325 kPa (abs) and 15 °C (59 °F) is 1.2250 kg/m3 (0.07647 lb/cu ft). At the non-standard sea level temperature of 20 °C (68 °F), the density would decrease to 1.204 kg/m3 (0.0752 lb/cu ft). This is about 1⁄800 that of water with a density of about 1,000 kg/m3 (62 lb/cu ft).

Air density is a property used in many branches of science, engineering, and industry, including aeronautics; gravimetric analysis; the air-conditioning industry; atmospheric research and meteorology; agricultural engineering (modeling and tracking of Soil-Vegetation-Atmosphere-Transfer (SVAT) models); and the engineering community that deals with compressed air.

Depending on the measuring instruments used, different sets of equations for the calculation of the density of air can be applied. Air is a mixture of gases and the calculations always simplify, to a greater or lesser extent, the properties of the mixture.

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