Gravimetrically-Prepared Carbon Dioxide Standards in Support of Atmospheric Research.

We have explored a one-step method for gravimetric preparation of CO₂-in-air standards in aluminum cylinders. We consider both adsorption to stainless steel surfaces used in the transfer of highly-pure CO₂, and adsorption of CO₂ to cylinder walls. We demonstrate that CO₂-in-air standards can be prepared with relatively low uncertainty (~ 0.04 %, ~ 95 % Confidence Level) by introducing aliquots whose masses are know to high precision, and by using well-characterized cylinders. Five gravimetric standards, prepared over the nominal range 350 to 490 μmol mol^-1 (parts per million, ppm), showed excellent internal consistency, with residuals from a linear fit equal to 0.05 ppm. This work compliments efforts to maintain the World Meteorological Organization, Global Atmosphere Watch, mole fraction scale for carbon dioxide, widely used for atmospheric monitoring. This gravimetric technique could be extended to other atmospheric trace gases, depending on the vapor pressure of the gas. [ABSTRACT FROM AUTHOR]