Conversion to PPM

  • Mariners - Seafarers

    I LOVE THIS SITE! But I have a question that I hope someone can help with. I was looking at the concentration of NO₂, SO₂ and PM2.5 and wanted to convert the reading into Parts Per Million (PPM). All the formulas I've found were for converting concentrations expressed in mass (in milligrams) per cubic meter (mg/m³); however the site is showing concentrations of Sulphur Dioxide per square meter (mg/m²), rather than per cubic meter. This doesn't make sense to me (meters squared vs meters cubed), and I believe is most likely an error, but this is far from my area of expertise, so I wanted to check and see if it is supposed to be mass per meter cubed (g/m³), or if mass per square meter is correct, what the formula would be to convert this reading to PPM? I found a conversion formula of Concentration (mg/m³) = 0.0409 X PPM X Molecular Weight.

    If anyone can help clarify I would appreciate it.

  • Sailor

    In the app, I see SO2 concentration in μg/m3 from GEOS-5 data:


    But on website it is mg/m2 from Copernicus data:

    Capture d’écran 2020-07-01 à 10.06.51.png

    It should be better to have the same data used both on website and in the app.

    Anyway the mg/m2 are probably an error as the Copernicus website shows SO2 amounts expressed in μg/m3.


  • Sailor

    SO2 data supplied by Copernicus are NOW corresponding to a column of this gas from ground to top of atmosphere and accordingly mg/m2 is the correct unit.
    Please, the description of SO2 layer in the FAQ should be changed :

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