Search results
Results from the WOW.Com Content Network
Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmospheric pressure, temperature and humidity. At 101.325 kPa (abs) and 20 °C (68 °F), air has a density of approximately 1.204 kg/m 3 (0.0752 lb/cu ft), according to the International Standard Atmosphere (ISA).
In this case, the unit is the centimeter cubed per gram (cm 3 /g or cm 3 ·g −1). To convert m 3 /kg to cm 3 /g, multiply by 1000; conversely, multiply by 0.001. Specific volume is inversely proportional to density. If the density of a substance doubles, its specific volume, as expressed in the same base units, is cut in half.
The density of air at sea level is about 1.2 kg/m 3 (1.2 g/L, 0.0012 g/cm 3). 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 ideal gas law). Atmospheric density decreases as the altitude increases.
Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 atm (101.325 kPa). Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 bar (100 kPa, 10 5 Pa).
Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations.The term "standard sea level" is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.
T is the temperature, T TPW = 273.16 K by the definition of the kelvin at that time; A r (Ar) is the relative atomic mass of argon and M u = 10 −3 kg⋅mol −1 as defined at the time. However, following the 2019 revision of the SI , R now has an exact value defined in terms of other exactly defined physical constants.
at each geopotential altitude, where g is the standard acceleration of gravity, and R specific is the specific gas constant for dry air (287.0528J⋅kg −1 ⋅K −1). The solution is given by the barometric formula. Air density must be calculated in order to solve for the pressure, and is used in calculating dynamic pressure for moving vehicles.
Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude. The change of atmospheric pressure with altitude can be obtained from this equation: [2]