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What is the current exact composition of Earth’s atmosphere?

I'm calibrating an instrument for measuring N2O fluxes, and my background gas corrections depend on highly accurate mixing ratios for N2, O2, and Ar. The textbook values seem outdated. I need a authoritative, citable source like from NOAA or the WMO that provides the current consensus numbers for the major and minor constituents of dry air, excluding variable gases like water vapor.

 

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By Rajiv Bhatia Answered 1 year ago

For precise work, I always refer to the latest WMO Greenhouse Gas Bulletin and the foundational data maintained by NOAA's Global Monitoring Laboratory. The current accepted dry-air mole fractions, determined from well-mixed background sites like Mauna Loa, are: N2 at 0.780848, O2 at 0.209390, and Ar at 0.009332. For your N2O calibration, the critical background values are CO2 at ~422 ppm, CH4 at ~1923 ppb, and N2O itself at ~336 ppb. Remember, these are well-mixed global background numbers; for local instrument calibration, you should use a certified standard gas traceable to these scales, as local air can have significant short-term variations.

 

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