Andrew Walkingshaw
J A Townsend
Peter Murray-Rust
Jim Downing
Sam Adams
Nick England
Sebastian Breuers
Hannah Barjat
Jens Thomas
A dictionary of non SI Units. These will necessarily have a multiplier to SI which
is not unity (except for degrees Celcius).
Units which are of unitType dimensionless, for example mg/kg should have that specific unit defined in
this dictionary. For pure numbers or concepts which cannot have dimensions such as method names you should use the
SI unit "none".
Wikipedia
Nick England
1/360th of a full rotation in a plane.
A degree is 1/360th of a full circle. 1 degree is equal to Pi/180 radians.
Wikipedia
Nick England
1 degree per minute
A rotation of one degree in one minute of time.
Wikipedia
Hannah Barjat
1 cm per second
A velocity of 1 cm per second.
Wikipedia
Andrew Walkingshaw
The smallest possible orbital radius for an electron in hydrogen in the
Bohr model.
Note that the definition of Bohr radius does not include the effect of
reduced mass, and so it is not precisely equal to the orbital
radius of
the electron in a hydrogen atom in the more physical model where
reduced
mass is included. This is done for convenience: the Bohr radius as
defined
above appears in equations relating to atoms other than hydrogen, where
the reduced mass correction is different. If the definition of
Bohr radius
included the reduced mass of hydrogen, it would be necessary to include a
more complex adjustment in equations relating to other atoms.
Wikipedia
Andrew Walkingshaw
1E-10 metres.
The angstrom is named after the Swedish physicist Anders Jonas Angstrom
(1814-1874), one of the founders of spectroscopy, after his
spectrum chart
of solar radiation in the electromagnetic spectrum on the order
of multiples of one ten-millionth of a millimetre, or 1E-10 metres.
Wikipedia
Hannah Barjat
One tenth of a metre.
Unit of length one tenth of a metre.
Wikipedia
Hannah Barjat
One hundredth of a metre.
Unit of length one hundredth of a metre.
Wikipedia
Nick England
1E-3 metres.
One thousandth of a metre.
Sebastian Breuers
1E-6 metres.
One 10-6th of a metre.
Sebastian Breuers
1E-9 metres.
One 10-9th of a metre.
Sebastian Breuers
1E-12 metres.
One 10-12th of a metre.
Wikipedia
Nick England
1E-15 metres.
One 10-15th of a metre.
Wikipedia
Hannah Barjat
1000 metres.
Unit of length equal to one thousand metres.
Wikipedia
Nick England
Angstrom Squared
The angstrom is named after the Swedish physicist Anders Jonas Angstrom
(1814-1874), one of the founders of spectroscopy, after his
spectrum chart
of solar radiation in the electromagnetic spectrum on the order
of multiples of one ten-millionth of a millimetre, or 1E-10 metres.
An Angstrom sqaured is the area of a square of length one angstrom.
Wikipedia
Hannah Barjat
Micrometre squared
Unit of area the square of one length of one micrometre.
Wikipedia
Hannah Barjat
Millimetre squared
Unit of area the square of one length of one millimetre.
Wikipedia
Hannah Barjat
Centimetre squared
Unit of area the square of one length of one centimetre.
Wikipedia
Hannah Barjat
Kilometre squared
Unit of area the square of one length of one kilometre.
Wikipedia
Hannah Barjat
10,000 square metres.
A unit of area equivalent to 10,000 square metres.
Wikipedia
Nick England
Angstrom Cubed
The angstrom is named after the Swedish physicist Anders Jonas Angstrom
(1814-1874), one of the founders of spectroscopy, after his
spectrum chart
of solar radiation in the electromagnetic spectrum on the order
of multiples of one ten-millionth of a millimetre, or 1E-10 metres.
An Angstrom cubed is the volume of a cube of length one angstrom.
Wikipedia
Hannah Barjat
Decimetre cubed (1/1000 of a cubic metre).
Unit of volume the cube of one length of one decimetre, known most commonly as a litre (or liter) but may also be known as a cubic decimetre.
Wikipedia
Hannah Barjat
Centimetre cubed.
Unit of volume the cube of one length of one centimetre. Also known as a millilitre 1 cm3 = 1 mL. It is sometimes also known as a 'cc' (e.g. in the automobile industry).
Wikipedia
Hannah Barjat
Millimetre cubed.
Unit of volume the cube of one length of one millimetre.
Wikipedia
Hannah Barjat
Micrometre cubed (μ3).
Unit of volume the cube of one length of one micrometre.
Wikipedia
Hannah Barjat
One part in 106 parts by volume.
The parts-per notation is a set of pseudo units to describe small values of dimensionless quantities. Where "by volume" is stated, the unit refers to the volume fraction, which is defined as the volume of a constituent divided by the volume of all consituents of the mixture prior to mixing. Volume fraction is also called volume concentration in ideal mixtures where the volumes of the constituents are additive (their sum equals the volume of the mixtures).
Wikipedia
Hannah Barjat
One part in 109 parts by volume.
The parts-per notation is a set of pseudo units to describe small values of dimensionless quantities. Where "by volume" is stated, the unit refers to the volume fraction, which is defined as the volume of a constituent divided by the volume of all consituents of the mixture prior to mixing. Volume fraction is also called volume concentration in ideal mixtures where the volumes of the constituents are additive (their sum equals the volume of the mixtures). [This latter meaning is commonly used in atmospheric chemistry where trace gases are measured within air samples.] NB. It is not uncommon for the 'V' to be left out of the symbol (for example within the atmospheric chemistry community), leading to ambiguity.
Wikipedia
Hannah Barjat
One part in 1012 parts by volume.
The parts-per notation is a set of pseudo units to describe small values of dimensionless quantities. Where "by volume" is stated, the unit refers to the volume fraction, which is defined as the volume of a constituent divided by the volume of all consituents of the mixture prior to mixing. Volume fraction is also called volume concentration in ideal mixtures where the volumes of the constituents are additive (their sum equals the volume of the mixtures). [This latter meaning is commonly used in atmospheric chemistry where trace gases are measured within air samples.].NB. It is not uncommon for the 'V' to be left out of the symbol (for example within the atmospheric chemistry community), leading to ambiguity.
Schwarz and Warneck, 1995
Hannah Barjat
Volume ratio expressed as cm3/m3.
These units of volume ratio are often used to describe the amount of a condensed phase within a gas phase medium e.g. cloud water within air.
Schwarz and Warneck, 1995
Hannah Barjat
Volume ratio expressed as μm3/m3.
These units of volume ratio are often used to describe the amount of a condensed phase within a gas phase med
ium e.g. particulate matter within air.
Wikipedia
Nick England
A density of 1E6 grams per cubic metre.
Density measured in megagrams per cubic metre.
Wikipedia
Hannah Barjat
1E-12 kg per cubic metre.
Mass density measured in nanograms per cubic metre.
Wikipedia
Hannah Barjat
1E-8 kg per cubic metre.
Mass density measured in nanograms per cubic centimetre.
Wikipedia
Hannah Barjat
1E8 kg per cubic metre.
Mass density measured in grams per cubic centimetre.
Wikipedia
Hannah Barjat
1E-3 kg per cubic metre.
Mass density measured in grams per cubic metre.
Wikipedia
Nick England
Number of electrons per cubic angstrom of volume.
Number of electrons per cubic angstrom of volume.
Wikipedia
Hannah Barjat
The Dobson unit (DU) is a unit of measurement of atmospheric ozone columnar density.
One Dobson unit refers to a layer of ozone that would be 10 μm thick under standard temperature and pressure. For example, 300 DU of ozone brought down to the surface of the Earth at 273.15K would occupy a layer only 3 mm thick. One DU is approximately equivalent to 2.69 x 1016 ozone molecules per square centimetre, or 2.69 x 1020 per square metre. This is 0.4462 millimoles of ozone per square metre.
Wikipedia
Hannah Barjat
Amount per area expressed in mmol per m2.
These are the IUPAC preferred units for the measurement of atmospheric ozone columar density (Schwarz and Warneck, 1995).
Schwarz and Warneck, 1995
Hannah Barjat
μmol.mol-1
Molefraction given in units of μmol.mol-1. Strictly speaking the quantity commonly denoted molefraction refers to the fraction that the amount of a substance contributes to the total amount of the sample, so that the correct name should be amount of substancefraction (a rather unwieldy term) or chemical amount fraction, as the name of a quantity should not involve the name of the unit. However, mole fraction is used by almost everyone without causing much confusion.
Schwarz and Warneck, 1995
Hannah Barjat
nmol.mol-1
Molefraction given in units of nmol.mol-1. Strictly speaking the quantity commonly denoted molefraction refers to the fraction that the amount of a substance contributes to the total amount of the sample, so that the correct name should be amount of substancefraction (a rather unwieldy term) or chemical amount fraction, as the name of a quantity should not involve the name of the unit. However, mole fraction is used by almost everyone without causing much confusion.
Schwarz and Warneck, 1995
Hannah Barjat
pmol.mol-1
Molefraction given in units of pmol.mol-1. Strictly speaking the quantity commonly denoted molefraction refers to the fraction that the amount of a substance contributes to the total amount of the sample, so that the correct name should be amount of substancefraction (a rather unwieldy term) or chemical amount fraction, as the name of a quantity should not involve the name of the unit. However, mole fraction is used by almost everyone without causing much confusion.
Schwarz and Warneck, 1995
Hannah Barjat
m-3.μ-1
Units used to describe the number of aerosols per cubic metre per length in microns (i.e. the number distribution of aerosols by their radius).
Wikipedia
Hannah Barjat
10-12 of a mole
10-12 of a mole.
Wikipedia
Hannah Barjat
10-9 of a mole
10-9 of a mole.
Wikipedia
Hannah Barjat
10-6 of a mole
10-6 of a mole.
Wikipedia
Hannah Barjat
10-3 of a mole
10-3 of a mole.
Wikipedia
Hannah Barjat
31557600 seconds
The Julian year is a time defined as exactly 365.25 days (i.e. averaging common and leap years). Fundamentally, expressing a time interval in Julian years is a way to precisely specify how many days (not how many "real" years). See also "Tropical year".
The symbol for year is not used consistently in scientific publications: a, a_j, y, yr etc may all be used.
Wikipedia
Hannah Barjat
31556925
The Tropical year is "the period of time for the ecliptic longitude of the Sun to increase by 360 degrees. Since the Sun's ecliptic longitude is measured with respect to the equinox, the tropical year comprises a complete cycle of the seasons. The mean tropical year is approximated by 365 days, 5 hours, 48 minutes, 45 seconds (31556925 seconds). This time period is also sometimes referred to as the mean Gregorian year (Schwarz and Warneck, 1995). NB. A further definition of year, using the symbol a (for annus), jointly adopted by the International Union of Pure and Applied Chemistry and the International Union of Geological Sciences is defined as the length of the tropical year in the year 2000 a = 31,556,925.445 seconds
The symbol for year is not used consistently in scientific publications: a, a_t, y, yr etc may all be used.
Wikipedia
Hannah Barjat
7 days (or 604800 seconds)
Based on S.I. units: a time period consisting of 7 days.
Wikipedia
Hannah Barjat
86400 seconds
Based on S.I. units: a time period consisting of 86400 seconds (24 hours). NB Other definitions of day are available: see source.
Wikipedia
Hannah Barjat
3600 seconds
A time period consisting of 3600 seconds (60 minutes).
Wikipedia
Nick England
60 seconds
A time period consisting of 60 seconds.
Sebastian Breuers
1E-3 seconds
One 10-3th of a second.
Sebastian Breuers
1E-6 seconds
One 10-6th of a second.
Sebastian Breuers
1E-9 seconds
One 10-9th of a second.
Sebastian Breuers
1E-12 seconds
One 10-12th of a second.
Sebastian Breuers
1E-15 seconds
One 10-15th of a second.
Wikipedia
Hannah Barjat
The number of occurences every 86400 seconds
The number of occurrences of a repeating event per day. NB Other definitions of day are available: see source.
Wikipedia
Hannah Barjat
The number of occurrences every 3600 seconds
The number of occurrences of a repeating event per hour.
Wikipedia
Hannah Barjat
The number of occurrences every 60 seconds
The number of occurrences of a repeating event per minute.
Wikipedia
Hannah Barjat
1000 Hz
The number of occurrences of a repeating event per millisecond.
Wikipedia
Hannah Barjat
1E6 Hz
The number of occurrences of a repeating event per microsecond.
Wikipedia
Hannah Barjat
1E9 Hz
The number of occurrences of a repeating event per nanosecond.
Wikipedia
Hannah Barjat
1E12 Hz
The number of occurrences of a repeating event per picosecond.
Wikipedia
Hannah Barjat
Rate of change in concentration expressed in units of molecules per cubic centimetre per second.
The rate of change in a molecular process e.g. in a first order chemical reaction.
The conversion to a molar concentration rate requires division by the Avagadro's constant, 6.02214179 x 1023 mol-1, to convert to moles and multiplication by 1E6 to convert to /m3
Wikipedia
Hannah Barjat
Rate of change in concentration expressed in units of molecules per cubic metre per second.
The rate of change in a molecular process e.g. in a first order chemical reaction.
The conversion to a molar concentration rate requires division by the Avagadro's constant, 6.02214179 x 1023 mol-1
Wikipedia
Hannah Barjat
Rate of change in concentration expressed in units of nanomoles per cubic centimetre per second.
The rate of change in a molecular process.
The conversion to a molar concentration rate requires division to convert to moles and multiplication by 1E6 to convert to /m3
Wikipedia
Hannah Barjat
Units of a bimolecular rate coefficient expressed in cm3 molecule-1 s-1.
Units of a second-order rate coefficient (k)
The conversion to a be used with molar quantities and other S.I. units requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1, to convert to moles and division by 1E6 to convert to m3
Wikipedia
Hannah Barjat
Units of a bimolecular rate coefficient expressed in m3 molecule-1 s-1.
Units of a second-order rate coefficient (k)
The conversion to a be used with molar quantities and other S.I. units requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1, to convert to moles.
Wikipedia
Hannah Barjat
Units of a termolecular rate coefficient expressed in cm6 molecule-2 s-1.
Units of a third-order rate coefficient (k)
The conversion to a be used with molar quantities and other S.I. units requires multiplication by the Avagadro's constant squared, to convert to moles and division by 1E12 to convert to m3
Wikipedia
Hannah Barjat
Units of a termolecular rate coefficient expressed in m6 molecule-2 s-1.
Units of a third-order rate coefficient (k)
The conversion to a be used with molar quantities and other S.I. units requires multiplication by the Avagadro's constant squared, to convert to moles
Wikipedia
Hannah Barjat
Number flux in molecule.m-2.s-1.
Number flux in molecules/m2/s. In this case flux is defined as the amount that flows through a unit area per unit time. For an example of use see Fick's First Law. These units may be used in experiments of deposition to, or emission from, a surface etc. With the units shown here the number flux refers to molecules but, in other cases number flux could relate to particles, radicals, photons etc (see photon_number_flux).
The conversion to to a be used with molar quantities requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1.
Wikipedia
Hannah Barjat
Number flux in photon.m-2.s-1.
Number flux in photons/m2/s. In this case flux is defined as the amount that flows through a unit area per unit time
The conversion to a be used with molar quantities requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1.
Wikipedia
Hannah Barjat
Number flux in particle.m-2.s-1.
Number flux in particles/m2/s. In this case flux is defined as the amount that flows through a unit area per unit time
For example, these units could be used in the measurement of the deposition of particles from the atmosphere to a surface.
Wikipedia
Hannah Barjat
Mass flux in mg.m-2.h-1.
Mass flux in mg/m2/h. In this case flux is defined as the mass that flows through a unit area per unit time. These units may be used in experiments of deposition to, or emission from, a surface etc.
Wikipedia
Hannah Barjat
Mass flux in mg.m-2.h-d.
Mass flux in mg/m2/day. In this case flux is defined as the mass that flows through a unit area per unit time. These units may be used in experiments of deposition to, or emission from, a surface etc.
Wikipedia
Hannah Barjat
Mass flux in µg.m-2.s-1.
Mass flux in µg/m2/s. In this case flux is defined as the mass that flows through a unit area per unit time. These units may be used in experiments of deposition to, or emission from, a surface etc.
Wikipedia
Hannah Barjat
Molecular absorption cross section in cm2.
The conversion to to a be used with molar quantities requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1.
Wikipedia
Hannah Barjat
Molecular absorption cross section in m2.
The conversion to to a be used with molar quantities requires multiplication by the Avagadro's constant, 6.02214179 x 1023 mol-1.
Wikipedia
Hannah Barjat
Molecule.photon-1
Quantum Yield units are dimensionless.
One thousanth of an amp.
One thousanth of an amp.
Wikipedia
Nick England
One thousand volts.
The kilovolt is a conveniently scaled measure for electric potential, electric potential difference, and electromotive force, equal to 1000 volts.
Wikipedia
Jens Thomas
The elementary charge, is the electric charge carried by a single proton, or equivalently,
the negation (opposite) of the electric charge carried by a single electron.
wikipedia entry
Sebastian Breuers
1012 Newton per mole.
1012 Newton per mole.
Wikipedia
Andrew Walkingshaw
The amount of kinetic energy gained by a single unbound electron
when it passes through an electrostatic potential difference of one
volt,
in vacuum.
The electronvolt is a very small unit, but is convenient for chemistry;
bond energies are of the order of 1eV per molecule.
Wikipedia
Hannah Barjat
1000 J.mol-1.
Physical quantities of energy transferred during phase transformations or chemical reactions, are almost always quoted in kJ·mol-1 rather than the S.I. J·mol-1 due to magnitudes involved.
Wikipedia
Jens Thomas
The Hartree is the atomic unit of energy, and is defined as:
E
h
=
2
R
∞
h
c
where R is the Rydberg constant, h the Plank constant and c the speed of light.
The Hartree is named after the British physicst Douglas Hartree, and is approximately
the electric potential energy of the hydrogen atom in its ground state and, by the virial theorem,
approximately twice its ionization energy; the relationships are not exact because of the finite mass
of the nucleus of the hydrogen atom and relativistic corrections.
wikipedia entry
Nick England
One thousand Watts.
One thousand Watts.
Nick England
1000 Pascals.
One thousand Pascals.
Wikipedia
Hannah Barjat
100 Pascals.
One hundred Pascals.
Wikipedia
Hannah Barjat
101325 Pascals.
101325 Pascals. The standard atmosphere is an international reference pressure defined as 101,325 Pa and it was formerly used as a unit of pressure. It truly reflects the mean sea level pressure for many of the industrialized nations (those with latitudes similar to Paris). Whilst it is no longer used as a unit, it is included for use with legacy documents.
Sebastian Breuers
100000 Pascals = 100 kPa.
Hundred thousand Pascals.
Wikipedia
Hannah Barjat
Temperature in ° C = Temperature in Kelvin - 273.15.
Celsius is a scale and unit of measurement for temperature. The unit was known until 1948 as centigrade.
Wikipedia
Nick England
Reciprocal Angstroms
TODO
Wikipedia
Nick England
A reciprocal millimetre.
TODO
Wikipedia
Hannah Barjat
A reciprocal centimetre.
A factor of 100 greater than a reciprocal metre. It is used, for example, in the description of absorption coefficients or, in spectroscopy, as the units of wavenumber.
Wikipedia
Hannah Barjat
1E12 kg.
The Petagram is a unit of mass equivalent to 1E15 grams.
Wikipedia
Hannah Barjat
1E9 kg.
The Teragram is a unit of mass equivalent to 1E12 grams.
Wikipedia
Hannah Barjat
1E3 kg.
The Megagram, also known as the tonne, is a unit of mass equivalent to 1E6 grams.
Wikipedia
Hannah Barjat
1E-3 kg.
The gram (also gramme in some British English texts), is a unit of mass equivalent to 1 thousandth of a kg.
Wikipedia
Hannah Barjat
1E-6 kg.
The milligram, is a unit of mass equivalent to 1E-3 g or 1E-6 kg.
Wikipedia
Hannah Barjat
1E-9 kg.
The microgram, is a unit of mass equivalent to 1E-6 g or 1E-9 kg.
Wikipedia
Hannah Barjat
1E-12 kg.
The nanogram, is a unit of mass equivalent to 1E-9 g or 1E-12 kg.
Wikipedia
Hannah Barjat
1E-15 kg.
The picogram, is a unit of mass equivalent to 1E-12 g or 1E-15 kg.
Nick England
1/12 of the mass of an atom of Carbon 12.
A definition of mass where the mass of an atom of Carbon 12 is defined to be 1 Dalton.