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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]
mg/m 3 = milligrams of pollutant per cubic meter of air at sea level atmospheric pressure and T: ppmv = air pollutant concentration, in parts per million by volume T = ambient temperature in K = 273. + °C 0.082057338 = Universal gas constant in L atm mol −1 K −1: M = molecular mass (or molecular weight) of the air pollutant
The gram (10 −3 kg) is an SI derived unit of mass. However, the names of all SI mass units are based on gram, rather than on kilogram; thus 10 3 kg is a megagram (10 6 g), not a *kilokilogram. The tonne (t) is an SI-compatible unit of mass equal to a megagram (Mg), or 10 3 kg.
The scale is a value or expression that is used as a factor to convert a value to its corresponding base unit. Commas may be used as a thousand separator (e.g. 1,000,000 ) or e notation may be used (e.g. 1e6 ).
In Earth's atmosphere, the pressure at sea level P 0 averages about 1.01 × 10 5 Pa, the mean molecular mass of dry air is 28.964 Da, and hence m = 28.964 Da × 1.660 × 10 −27 kg/Da = 4.808 × 10 −26 kg. As a function of temperature, the scale height of Earth's atmosphere is therefore H/T = k/mg = 1.381 × 10 −23 J⋅K −1 / (4.808 × ...
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= molar mass of Earth's air: 0.0289644 kg/mol The value of subscript b ranges from 0 to 6 in accordance with each of seven successive layers of the atmosphere shown in the table below. The reference value for ρ b for b = 0 is the defined sea level value, ρ 0 = 1.2250 kg/m 3 or 0.0023768908 slug/ft 3 .
Since all gases have the same volume per mole at a given temperature and pressure far from their points of liquefaction and solidification (see Perfect gas), and air is about 1 / 5 oxygen (molecular mass 32) and 4 / 5 nitrogen (molecular mass 28), the density of any near-perfect gas relative to air can be obtained to a good ...