# Parts per Million - ppm

* Parts per million - ppm * - is commonly used as a dimensionless measure of ** small levels ** (concentrations) of pollutants in air, water, body fluids, etc.

* Parts per million * is the molar mass, volume or mass ratio between the pollutant component and the solution. * ppm * is defined as

ppm = 1,000,000 c / s

= 10^{6}c / s (1)

where

c = molar mass, volume or mass of the solute component (mole, m^{3}, ft^{3}, kg, lb_{m})

s = molar mass, volume or mass of the solution (mole, m^{3}, ft^{3}, kg, lb_{m})

In the metric system * ppm * for mass can be expressed in terms of * milligram versus kg * where

1 mg/kg = 1 part per million

* ppm * can be also be expressed as

*1 ppm = 10*^{-6}= 0.0001 % = 0.001 ‰

*1 000 ppm = 0.1 %*

*10 000 ppm = 1%*

Download and print ppm vs. percent and mg/L chart

Alternatively - mass related units to measure very small concentration levels:

- ppb - parts per billion (1 / 1,000,000,000 or 10
^{-9}) *ppt - parts per trillion (1 / 1,000,000,000,000 or 10*^{-12})*ppq - parts per quadrillion (1 / 1,000,000,000,000,000 or 10*^{ -15 })

An alternatively mass related unit to measure larger concentration levels is * weight percent * which can be expressed as

weight percent = 100 m_{ c }/ m_{ s }(2)

### ppm vs. Mass per Unit Volume

The concentration of a component can be measured as mass per unit volume - like * mg/liter, mg/cm *^{3} 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 (mg/L)

= 1 microlitre ( μL ) per liter

= 0.001 gram per litre

= 8.345 pounds per million gallons of water

#### Example - Volume Concentration of Carbon Dioxide in Air

The concentration of carbon dioxide in air is aprox. * 400 ppm * . The volume of carbon dioxide in one * 1 m ^{3} * of air can be calculated by modifying

*(1)*to

* c = ppm s / 10 ^{6} *

* = (400 ppm) (1 m ^{3} ) / 10^{6} *

* = 0.0004 m ^{3} /m^{3} *

### Percent by Volume

Volume percent can be expressed as volume per unit volume:

percent by volume = 100 v_{ c }/(v_{ c }+ v_{ s }) (3)

where

v_{ c }= volume component

v_{ s }= 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 divided by kilograms of solvent.

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