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Converting % Dissolved oxygen to mg/L

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  • Converting % Dissolved oxygen to mg/L

    Does anyone know how to convert % dissolved oxygen to milligrams per liter?

  • #2
    Re: Converting % Dissolved oxygen to mg/L

    There are tables or formulas that express the maximum (saturated) O2 as a function of temperature, pressure, and salinity in mg/L. Detrmine saturated value, then multiply by the given percentage.

    This Wikipedia article is a place to start (skip over the blood section), The formula for water considers salinity and temperature, but not pressure. Follow the link to the USGS site for a pdf document with tables. They include pressure. http://en.wikipedia.org/wiki/Oxygen_saturation

    Much like water vapor in air for humidity calculations, it is not a trivial conversion

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    • #3
      Re: Converting % Dissolved oxygen to mg/L

      Here is an "official" (web copy) of the USGS memo on calculating this. http://water.usgs.gov/admin/memo/QW/qw81.11.html
      It is the only method accepted for USGS work. It contains typos probably related to conversion to the web. (missing minus signs, superscripts, etc)

      This document is a "readme" for an Excel spreadsheet that implements the method. The author mentions the typos above and formula corrections he made (see Table 1) to get results in agreement with USGS tables. http://science.nature.nps.gov/im/uni...tor_Readme.doc

      I think between the two, you can duplicate the math.

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      • #4
        Re: Converting % Dissolved oxygen to mg/L

        Perhaps it's just me as I'm not seeing it. Although the links that you've provided are great, but the equation(s) are for calculating DO saturation, using atmospheric pressure, temp, and salinity, and didn't show anything on how to convert DO mg/L to DO saturation.

        I know this is an old questions, so hopefully you'll come across it and provide some additional insight.

        Thanks :-)

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        • #5
          Re: Converting % Dissolved oxygen to mg/L

          Originally posted by Unregistered View Post
          Perhaps it's just me as I'm not seeing it. Although the links that you've provided are great, but the equation(s) are for calculating DO saturation, using atmospheric pressure, temp, and salinity, and didn't show anything on how to convert DO mg/L to DO saturation.

          I know this is an old questions, so hopefully you'll come across it and provide some additional insight.

          Thanks :-)
          You have to calculate the saturated value for the conditions, then

          Percent_Saturation = actual_DO/saturated_DO * 100%

          or actual_DO = (Percent_Saturation/100) * saturated_DO

          Saturation percentage is somewhat like relative humidity; it is a fraction of what the medium is capable of holding. The saturation value must be calculated.

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          • #6
            Re: Converting % Dissolved oxygen to mg/L

            Originally posted by Unregistered View Post
            Does anyone know how to convert % dissolved oxygen to milligrams per liter?
            0.115686275 mg/L per 1%

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            • #7
              Re: Converting % Dissolved oxygen to mg/L

              P1V1=P2V2

              hope this formula helps.

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              • #8
                Re: Converting % Dissolved oxygen to mg/L

                Originally posted by Unregistered View Post
                0.115686275 mg/L per 1%
                how reliable is this conversion?

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                • #9
                  Re: Converting % Dissolved oxygen to mg/L

                  Originally posted by Unregistered View Post
                  how reliable is this conversion?
                  It is perfect when saturated_DO is exactly 11.5686275 mg/L (about 9 C, 760 mm) and wrong the rest of the time. Saturated DO is a complex function of temperature, pressure and salinity. See the tables referred to in the above links to see how much it varies with these parameters. There is no shortcut.

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                  • #10
                    Re: Converting % Dissolved oxygen to mg/L

                    I need to convert a DO reading in mg/L to a percentage.

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                    • #11
                      Re: Converting % Dissolved oxygen to mg/L

                      Originally posted by Unregistered View Post
                      I need to convert a DO reading in mg/L to a percentage.
                      As above, you need the temperature and salinity of the water and the atmospheric pressure so you can calculate the saturate value of DO at the conditions. Then divide actual by saturated to get a decimal fraction and multiply by 100% for percent.

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                      • #12
                        Re: Converting % Dissolved oxygen to mg/L

                        Can anyone post the formula please

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                        • #13
                          Hi there,

                          i wrote an oxygen converter. It uses the formula from Green & Carrit.

                          You can find it here:

                          http://www.loligosystems.com/convert...-units?menu=77

                          Hope this helps.

                          Cheers

                          Erik
                          Last edited by Erik; 10-22-2014, 05:03 AM.

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                          • #14
                            Double post, sorry

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