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Nitrogen-Ion Conversion Chart

There are two major ways to describe the concentrations of ammonia, nitrite, and nitrate in water. The "nitrogen" weight of these molecules describes the weight of only the nitrogen atoms within them. On the other hand, the "ion" weight of these molecules describes the weight of the entire molecule.

For example, the term nitrate-nitrogen (NO3-N) refers to the weight of only the nitrogen atom within the nitrate molecule; as opposed to nitrate-ion (NO3), which describes the weight of the entire nitrate molecule. Note that a given nitrate-nitrogen value will always be lower than the associated nitrate-ion value. Conversion between the two forms is as simple as applying a constant (see graph below).

Scientific literature often uses the "nitrogen" form rather than the "ion" form to describe the concentration for these molecules. The "nitrogen" form is more appropriate when discussing nitrification/denitrification cycles, as it simplifies various equations and flow-charts. For example, it is easy to see that 100 ppm of nitrite-nitrogen (NO2-N) can go on to form 100 ppm of nitrate-nitrogen (NO3-N). Using the "ion" form here would be more cumbersome; 100 ppm of nitrite (NO2) goes on to form approximately 135 ppm of nitrate (NO3).

Note that a total ammonia value (NH3 + NH4) cannot be trivially converted from "nitrogen" to "ion" form or vice versa. The total ammonia value must first be broken into component NH3 and NH4 values, then those converted individually to NH3-N and NH4-N and added together. The Free Ammonia Calculator can be used to do this.

NH3 = NH3-N * 1.21589
NH4 = NH4-N * 1.28786
NO2 = NO2-N * 3.28443
NO3 = NO3-N * 4.42664

Assumed atomic weights:
H: 1.008, N: 14.007, O: 15.999

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