Gravimetrically-Prepared Carbon Dioxide Standards in Support of Atmospheric Research

Abstract. We have explored a one-step method for gravimetric preparation of CO 2 -in-air standards in aluminum cylinders. We consider both adsorption to stainless steel surfaces used in the transfer of highly-pure CO 2 , and adsorption of CO 2 to cylinder walls. We demonstrate that CO 2 -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.