ppm - parts per million
ppm - parts per million - is commonly used as unit of concentration
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Parts per million - ppm - is commonly used as a measure of small levels of pollutants in air, water, body fluids, etc. Parts per million is the mass ratio between the pollutant component and the solution and ppm is defined as
ppm = 1,000,000 mc / ms (1)
where
mc = mass of component (kg, lbm)
ms = mass of solution (kg, lbm)
In the metric system ppm can be expressed in terms of milligram versus kg where
- 1 mg/kg = 1 part per million
Alternatively mass related units to measure very small concentration levels used are
- ppb - parts per billion (1 / 1,000,000,000)
- ppt - parts per trillion (1 / 1,000,000,000,000)
An alternatively mass related unit to measure larger concentration levels are weight percent which can be expressed like
weight percent = 100 mc / ms (2)
Volume related Concentration Units
Mass per Unit Volume
The concentration of a component can be measured as mass per unit volume as mg/liter, mg/cm3, etc.
Weight of substance added to one unit volume of water to give one part per million (ppm)
1 ppm
= 2.72 pounds per acre-foot
= 1,233 grams per acre-foot
= 1.233 kilograms per acre-foot
= 0.0283 grams per cubic foot
= 0.0000624 pounds per cubic foot
= 0.0038 grams per US gallon
= 0.058419 grains per US gallon
= 0.07016 grains per Imperial gallon
= 1 milligram per liter
= 1 microlitre ( μL ) per liter
= 0.001 gram per litre
= 8.345 pounds per million gallons of water
Percent by Volume
Volume percent can be expressed as volume per unit volume as
percent by volume = 100 vc /(vc + vs) (3)
where
vc = volume component
vs = volume solvent
Molarity
Molarity is the number of moles of solute (substance of interest - pollution, etc.) dissolved in one liter (volume) of the solution.
Molality
Molality is the number moles of solute dissolved in one kg (mass) of the solution.
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