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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]
As an example, a measured particulates concentration of 200 mg/m 3 in a dry gas that has a measured 8 volume % CO 2 is: 200 × ( 12 ÷ 8 ) = 300 mg/m 3. when corrected to a dry gas having a specified reference CO 2 content of 12 volume %.
For some usage examples, consider the conversion of 1 SCCM to kg/s of a gas of molecular weight , where is in kg/kmol. Furthermore, consider standard conditions of 101325 Pa and 273.15 K, and assume the gas is an ideal gas (i.e., =).
For example, IUPAC has, since 1982, defined standard reference conditions as being 0 °C and 100 kPa (1 bar), in contrast to its old standard of 0 °C and 101.325 kPa (1 atm). [2] The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m).
A number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article.
Xchanger Inc, webpage Calculator for SCFM, NM3/hr, lb/hr, kg/hr, ACFM & M3/hr gas flows. onlineflow.de, webpage Online calculator for conversion of volume, mass and molar flows (SCFM, MMSCFD, Nm3/hr, kg/s, kmol/hr and more) ACFM versus SCFM for ASME AG-1 HEPA Filters; SCFM (Standard CFM) vs. ACFM (Actual CFM) (Specifically for air flows only)
In fractions like "2 nanometers per meter" (2 n m / m = 2 nano = 2×10 −9 = 2 ppb = 2 × 0.000 000 001), so the quotients are pure-number coefficients with positive values less than or equal to 1. When parts-per notations, including the percent symbol (%), are used in regular prose (as opposed to mathematical expressions), they are still pure ...
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.