How do I convert MMR to VMR?

Most of the chemical species in CAMS Global data are archived as mass mixing ratios (MMR, kg of gas / kg of air).

## Convert MMR to mass concentration (e.g. in kg/m3)

To compute mass concentration (mass per volume unit) apply this formula:
\rho_x = \alpha_x \frac{p}{RT}

or

\rho_x = \alpha_x \rho

Where \rho_x (kg/m^3) is concentration of a chemical species, \alpha_x(kg/m^3) is mass mixing ratio, p(Pa, 1 Pa = 0.01 hPa) , T(K) and \rho(kg/m^3) are ambient pressure, temperature and density and R is the specific gas constant (for dry air 287.058 \frac{J}{kgK} ).

## Convert MMR to Volume Mixing Ratio (VMR, units ppmv or ppbv)

To convert data from MMR to VMR you only need molar masses of dry air and molar mass of the atmospheric species. See here for more information (page 9). For example:- For O3, the formula is: VMR = 28.9644 / 47.9982 * 1e9 * MMR
- For CO the formula is: VMR = 28.9644 / 28.0101 * 1e9 * MMR
- For NO2 the formula is: VMR = 28.9644 / 46.0055 * 1e9 * MMR
- For SO2 the formula is: VMR = 28.9644 / 64.0638 * 1e9 * MMR
- For CO2 the formula is: VMR = 28.9644 / 44.0095 * 1e9 * MMR
- For CH4 the formula is: VMR = 28.9644 / 16.0425 * 1e9 * MMR

The 1e9 in the formulae gives parts per billion (ppbv), use 1e6 to get parts per million (ppmv).

## Dobson Unit (DU)

DU is a vertically integrated quantity and can only be used for total or partial column parameters. To convert total column Ozone data from kg/m2 into DU, multiply the values by 46698. See also What is the Dobson Unit (DU)? and How to convert Ozone units from µg/m3 to Dobson Unit?sudurbhai kela..sutmarani kobo nuwaro kiba hudhile

Thank you so much for this, really helped!