airdensity

Airdensity, more commonly written as air density, is the mass of air per unit volume. It is typically expressed in kilograms per cubic meter (kg/m^3) and is a key property of the Earth's atmosphere that influences aerodynamics, weather, and ventilation. Air density depends on the state of the air, including its pressure, temperature, humidity, and chemical composition.

Under the ideal gas approximation, density is described by the equation rho = p / (R_specific * T), where p is pressure, T is absolute temperature, and R_specific is the specific gas constant for the air (about 287.05 J/(kg·K) for dry air). Humidity affects density because water vapor has a lower molecular weight than dry air; at a given pressure and temperature, humid air is slightly less dense than dry air. In practice, air density decreases with increasing temperature and increases with rising pressure. Altitude also plays a major role, with density diminishing as elevation and atmospheric pressure fall.

Standard reference values place sea-level dry air density at about 1.225 kg/m^3 at 15°C (288.15 K) and 101.3 kPa. In humid or warmer conditions, the density is somewhat lower. Air density is a fundamental input for calculations in aviation (lift, drag, engine performance), meteorology (air masses and weather systems), and building systems (HVAC design and indoor air quality).

See also: air pressure, temperature, humidity, standard atmosphere, aerodynamics.