Parts per million
Parts per million (ppm) is a unit of measure used to measure concentration. Determine a tolerance range. It refers to the number of units of a certain substance (agent, etc.) that there are per million units of the set.
In science and engineering, the parts per notation is a set of pseudo-units used to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-by-quantity measures, they are pure numbers with no associated units of measure. Commonly used ones are parts per million ('ppm, 10−6), parts per billion' (ppb, 10−9), parts per trillion (ppt, 10 −12) and parts per quadrillion (ppq, 10−15). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous.
Features
It is a concept homologous to the percentage, only that in this case it is not parts per percent but per million (both per thousand).
General mass formulas
ppm=Component mass (g)Total mass of dissolution (g)⋅ ⋅ 106{displaystyle ppm={frac {text{Masa del component (g)}{{{mbox{Total dissolution mass}}}}}cdot 10^{6}}}}}
Alternatively, using the kilogram as a reference:
ppm=milligrams of solute (mg)kilogram of dissolution (kg){displaystyle ppm={frac {mbox{miligramos de soluto (mg)}{{mbox{kilogram de dissolution (kg}}}}}}}}
Using microgram as reference:
ppm=microgram of solute (μg)gram of dissolution (g){displaystyle ppm={frac {mbox{microgram of solute (μg)}{{mbox{gram of dissolution (g}}}}}}}}
General formulas in volume
ppm=milligrams of solute (mg)litre of dissolution (L){displaystyle ppm={frac {mbox{miligramos de soluto (mg)}{mbox{litro de dissolution (L}}}}}}}}
Similarly, using the microgram as a reference:
ppm=microgram of solute (μg)milliliter of dissolution (ml){displaystyle ppm={frac {mbox{microgramo de soluto (μg)}{{mbox{mililitro de dissolution (ml}})}}}}
You can use ppmm (with extra m at the end) for parts by mass, or ppmv for parts by volume.
In fact, the following equivalence could be taken:
- 10 000 ppm = 1 %
So 10,000 ppm equals one percent. From the above, it can be deduced that this unit is used analogously to the percentage but for much lower concentrations or values. For example, when talking about concentrations of pollutants in water or air, solutions with very low concentrations or amount of dust particles in an environment, among others.
Use
Using ppm as a unit speeds up communication between a given signal and a certain percentage. For example, in a million grains of rice, if one were painted black, this grain would represent one (1) part per million which is abbreviated as “ppm”. Some cases:
- Chemical analysis of water: ppm refers to mg of analyte per litre of water; mg/L (equivalent to ug/mL). For example: Clorouros = 20 ppm equivalent to 20 mg/L as Cl- What do you mean, 20 milligrams of ion chloride per litre of water.
- Air Pollutants: ppm refers to parts of steam or gas per million parts of contaminated air; cm3/m3. Another way of expressing it is in mg/m3, of what arises a conversion factor that depends on the physical properties of each contaminant. For example, for benzene the conversion factor is 1 ppm = 3.19 mg/m3.
- Mineral trace analysis; ppm refers to g of analyte per ton of mineral; g/t or mg/kg
- Statistics: ppm means one case every one million cases of the population under study.
- Tolerance: ppm means an uncertainty of a millionth of measurement.
Just like when using percentage, it may be necessary to clarify if they are parts by volume, mass or weight, if they refer to a dry basis, etc.
Criticism of the use of the expression "parts by"
Although the International Bureau of Weights and Measures (an international standards organization also known by its French initials BIPM) recognizes the use of the "parts by" notation, it is not formally part of the International System of Units (SI). It should be noted that although "percentage" (%) is not formally part of the SI, both the BIPM and the International Organization for Standardization (ISO) take the position that "in mathematical expressions, the internationally recognized symbol % (percentage) can be used with the SI to represent the number 0.01" for dimensionless quantities. ppb and ppt". Although SI-compatible expressions should be used as an alternative, the "parts per" It is still widely used in technical disciplines. The main problems with the notation of parts by are given below.
Long and short numerical scales
Since number names beginning with the word "billion" have different values in different countries, the BIPM suggests avoiding the use of "ppb" and "ppt" to avoid bad blood. The National Institute of Standards and Technology (NIST) of the United States adopts an inflexible position, indicating that "terms that are dependent on the language [...] are not acceptable to be used with the SI to express the values of quantities".
Mass fraction - mole fraction - volume fraction
Another problem with "parts by" is that it can refer to mass fraction, mole fraction, or volume fraction. Since it is not usually stated which quantity is used, it is better to write the unit as kg/kg, mol/mol, or m3/m3 (although they are all dimensionless). The difference is quite significant when it comes to gases, and it is very important to specify what quantity is being used. For example, the conversion factor between a 1 ppb mass fraction and a 1 ppb mole fraction is approximately 4.7 for the greenhouse gas CFC-11 in air. For volume fraction, the suffix "V" or "v" it is sometimes added to the parts-by notation (for example, ppmV, ppbv, pptv). Unfortunately, ppbv and pptv are also often used for mole fractions (which is identical to volume fraction only for ideal gases)..
To distinguish the mass fraction from the volume fraction or mole fraction, the letter "w" (meaning "weight"- "weight" in English) to the abbreviation (for example, ppmw, ppbw).
Using the "parts per" it is usually quite fixed within each specific branch of science, but often in a way that is inconsistent with its use in other branches, leading some researchers to assume that their own use (mass/mass, mol/ mole, volume/volume, or others) is correct and that other usages are incorrect. This assumption sometimes leads them not to specify the details of their own usage in their posts, and thus others may misinterpret their results. For example, electrochemists often use volume/volume, while chemical engineers may use mass/mass as well as volume/volume. Many high-level academic publications do not specify their use of the notation.