Units module

This module contains the definitions of the units, as well as the unit-registry object ureg.

Main units

• general mass units (g, t and their association with prefixes like kg, Mt, etc)

• length and volume units like m, L, m**3

• time units (year, month, week, day)

In addition, the following units are defined in unit_definitions.txt.

percent = [] = 0.01*count = %

ton = 1 * tonne
kt = 1000 * tonne
kton = 1000 * tonne

# elements

C = [carbon]
CO2 = [carbon_dioxide] = 12/44 * [carbon]
CO2e = [carbon_dioxide_equivalent]
CH4 = [methane]

N = [nitrogen]
NH3 = [ammonia]
N2O = [nitrous_oxide]
NOx = [nitrogen_oxides]

P = [phosphorus]
P2O5 = [phosphorus_pentoxide]
PO4e = [phosphate_equivalent]

S = [sulfur]
SO2 = [sulfur_dioxide]
SO2e = [sulfur_dioxide_equivalent]

K = [potassium]
K2O = [potassium_oxide]

Na = [sodium]

Ca = [calcium]

Cl = [chloride]

Mg = [magnesium]

H2O = [water]

Fe = [iron]

These units are then combined to g and t so you can use directly gN, gP, or tCO2e.

Any unit that is not directly defined here can be acces via the ureg object.

Please see the Pint documentation for more details on how to use units.

Contexts

In addition to the units, the unit_definitions.txt file defines contexts that are used to convert between different units.

The following contexts are defined:

• “elements”, to convert a mass of molecules to the mass of one of its basic components (e.g. amount of carbon in or ),

• “AR4GWP100” (or just “GWP”, global warming potential), to convert greenhouse gases to over a 100 year period,

• “eutrophication”, to convert phosphorus-related molecules to (phosphate equivalents),

• “acidification”, to convert sulfur-related molecule to .

For each of them, you can convert a quantity q to another unit u under context c via q.to(u, c).

@context elements = el
    [mass]*[carbon_dioxide] -> [mass]*[carbon]: 12/44 * value / CO2 * C
    [mass]*[methane] -> [mass]*[carbon]: 12/16 * value / CH4 * C

    [mass]*[ammonia] -> [mass]*[nitrogen]: 14/17 * value / NH3 * N
    [mass]*[nitrous_oxide] -> [mass]*[nitrogen]: 28/44 * value / N2O * N
    [mass]*[nitrogen_oxides] -> [mass]*[nitrogen]: 0.3 * value / NOx * N

    [mass]*[phosphorus] -> [mass]*[phosphorus_pentoxide]: 142/62 * value / P * P2O5
    [mass]*[phosphorus_pentoxide] -> [mass]*[phosphorus]: 62/142 * value / P2O5 * P

    [mass]*[potassium_oxide] -> [mass]*[potassium]: 0.4107 * value / K2O * K
    [mass]*[potassium] -> [mass]*[potassium_oxide]: 2.409 * value / K * K2O

    [mass]*[sulfur] -> [mass]*[sulfur_dioxide]: 2 * value / S * SO2
    [mass]*[sulfur_dioxide] -> [mass]*[sulfur]: 0.5 * value / SO2 * S
@end


@context AR5GWP100 = GWP100 = GWP = gwp
    [mass]*[carbon_dioxide] -> [mass]*[carbon_dioxide_equivalent]: value / CO2 * CO2e
    [mass]*[methane] -> [mass]*[carbon_dioxide_equivalent]: 27 * value / CH4 * CO2e
    [mass]*[nitrous_oxide] -> [mass]*[carbon_dioxide_equivalent]: 273 * value / N2O * CO2e
@end


@context eutrophication = EP = ep
    [mass]*[phosphorus] -> [mass]*[phosphate_equivalent]: value / P * PO4e
    [mass]*[phosphorus_pentoxide] -> [mass]*[phosphate_equivalent]: 2 * value / P2O5 * PO4e
@end


@context acidification = AP = ap
    [mass]*[sulfur] -> [mass]*[sulfur_dioxide_equivalent]: value / S * SO2e
    [mass]*[sulfur_dioxide] -> [mass]*[sulfur_dioxide_equivalent]: value / SO2 * SO2e
@end