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In most other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values. Although ppmv and mg/m 3 have been used for the examples in all of the following sections, concentrations such as ppbv (i.e., parts per billion by volume), volume percent, mole percent and many others may also be used for gaseous pollutants.
Pollution regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. In most other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values. 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
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 unit is in common use for masses above about 10 3 kg and is often used with SI prefixes.
1.0 long cwt (110 lb; 51 kg) short hundredweight: short cwt short cwt 1.0 short cwt (100 lb; 45 kg) long quarter: long qtr long qtr 1.0 long qtr (28 lb; 13 kg) short quarter: short qtr short qtr 1.0 short qtr (25 lb; 11 kg) stone: st st 14 lb used mostly in the British Commonwealth except Canada 1.0 st (14 lb; 6.4 kg) st kg. st kg lb; st lb
The conversion between different SI units for one and the same physical quantity is always through a power of ten. This is why the SI (and metric systems more generally) are called decimal systems of measurement units. [10] The grouping formed by a prefix symbol attached to a unit symbol (e.g. ' km ', ' cm ') constitutes a new inseparable unit ...
= 205.196 548 3 mg carat (metric) ct ≡ 200 mg = 200 mg clove: ≡ 8 lb av = 3.628 738 96 kg: crith: ≡ mass of 1 L of hydrogen gas at STP: ≈ 89.9349 mg dalton: Da 1/12 the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest: ≈ 1.660 539 068 92 (52) × 10 −27 kg [20] dram (apothecary ...
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.
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).