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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 %.
With this conversion from SCCM to kg/s, one can then use available unit calculators to convert kg/s to other units, [5] such as g/s of the CGS system, or slug/s. Based on the above formulas, the relationship between SCCM and molar flow rate in kmol/s is given by
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)
For example, the conversion factor between a mass fraction of 1 ppb and a mole fraction of 1 ppb is about 4.7 for the greenhouse gas CFC-11 in air (Molar mass of CFC-11 / Mean molar mass of air = 137.368 / 28.97 = 4.74). For volume fraction, the suffix "V" or "v" is sometimes appended to the parts-per notation (e.g. ppmV, ppbv, pptv).
Using the number density of an ideal gas at 0 °C and 1 atm as a yardstick: n 0 = 1 amg = 2.686 7774 × 10 25 m −3 is often introduced as a unit of number density, for any substances at any conditions (not necessarily limited to an ideal gas at 0 °C and 1 atm). [3]
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.
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.