User:Milton Beychok/Sandbox: Difference between revisions
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==Parts per billion (ppb)== | ==Parts per billion (ppb)== | ||
In ordinary prose, 1 ppb is one part per billion parts and has a value of 1 × 10<sup>-9</sup> in the United States only. This terminology should be used with great caution because: | In ordinary prose, 1 ppb is one part per billion parts and has a value of 1 × 10<sup>-9</sup> in the [[United States]] only. This terminology should be used with great caution because: | ||
*In France and frequently in continental Europe, 1 × 10<sup>-9</sup> is ''1 milliard'' | *In [[France]] and frequently in continental [[Europe]], 1 × 10<sup>-9</sup> is ''1 milliard'' | ||
*In the United Kingdom and in other nations using British English, 1 × 10<sup>-9</sup> is ''1 thousand million'' and 1 billion is 1 × 10<sup>-12</sup> | *In the [[United Kingdom]] and in other nations using [[British English]], 1 × 10<sup>-9</sup> is ''1 thousand million'' and 1 billion is 1 × 10<sup>-12</sup> | ||
==Parts per trillion (ppt)== | ==Parts per trillion (ppt)== | ||
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The [[International Bureau of Weights and Measures]] (an international standards organization known also by its [[France|French]]-language initials BIPM) recognizes the use of parts-per notation.<ref name="BIPM">BIPM: [http://www.bipm.org/en/si/si_brochure/chapter5/5-3-7.html 5.3.7 ''Stating values of dimensionless quantities, or quantities of dimension one]''</ref> However, the BIPM suggests avoiding the use of ppb and ppt to avoid misunderstandings. | The [[International Bureau of Weights and Measures]] (an international standards organization known also by its [[France|French]]-language initials BIPM) recognizes the use of parts-per notation.<ref name="BIPM">BIPM: [http://www.bipm.org/en/si/si_brochure/chapter5/5-3-7.html 5.3.7 ''Stating values of dimensionless quantities, or quantities of dimension one]''</ref> However, the BIPM suggests avoiding the use of ppb and ppt to avoid misunderstandings. | ||
Perhaps the best practice is to use the scientific | Perhaps the best practice is to use the [[scientific notation]]s 1 × 10<sup>-6</sup>, 1 × 10<sup>-9</sup> and 1 × 10<sup>-612</sup> to avoid misundersatndings. | ||
==References== | ==References== | ||
{{reflist}} | {{reflist}} | ||
Revision as of 22:19, 9 August 2008
“Parts-per” notation is used in science and engineering, to denote proportionalities in measured quantities such as proportions at the parts-per-million (ppm), parts-per-billion (ppb), and parts-per-trillion (ppt) level. Since parts-per notations are quantity-per-quantity measures, they are known as dimensionless quantities; that is, they are pure numbers with no associated units of measurement.
Parts per million (ppm)
In ordinary prose, 1 ppm is "one part per million parts" and has a numerical value of 1 × 10-6 in most (if not all countries).
Parts-per notation is often used in the measure of dilutions (concentrations) in chemistry; for instance, for measuring the relative abundance of dissolved minerals or pollutants in water. The expression 1 ppm means a given property exists at a proportion of one part per million parts examined, as would occur if a water-borne pollutant was present at a concentration of one-millionth of a gram per gram of sample solution.
Similarly, parts-per notation is used also in physics and engineering to express the value of various proportions. For example, a metal might expand 1.2 micrometre per metre of length for every degree Celsius and this would be expressed as a Coefficient of thermal expansion of 1.2 ppm/°C. As another example, the accuracy of land-survey distance measurements when using a laser rangefinder might be 1 millimetre per kilometre of distance and this could be expressed as an accuracy of 1 ppm.
Parts per billion (ppb)
In ordinary prose, 1 ppb is one part per billion parts and has a value of 1 × 10-9 in the United States only. This terminology should be used with great caution because:
- In France and frequently in continental Europe, 1 × 10-9 is 1 milliard
- In the United Kingdom and in other nations using British English, 1 × 10-9 is 1 thousand million and 1 billion is 1 × 10-12
Parts per trillion (ppt)
In ordinary prose, 1 ppt is one part per trillion parts and has a value of 1 × 10-12 again in the United States only. This terminology should also be used with great caution because:
- In the United Kingdom and other nations using British English, France and continental Europe, 1 × 10-12 is 1 billion and 1 trillion is 1 × 10-18
- Concentrations are sometimes expressed as ppt meaning parts per thousand which conflicts with ppt meaning parts per trillion.
Summary
The parts-per notation is not formally part of the International System of Units (SI).
The International Bureau of Weights and Measures (an international standards organization known also by its French-language initials BIPM) recognizes the use of parts-per notation.[1] However, the BIPM suggests avoiding the use of ppb and ppt to avoid misunderstandings.
Perhaps the best practice is to use the scientific notations 1 × 10-6, 1 × 10-9 and 1 × 10-612 to avoid misundersatndings.