Abstract
A new, lightweight instrument has been developed for measuring atmospheric mixing ratios of the greenhouse gas carbon dioxide with high precision and accuracy. This modified total organic carbon analyzer uses a bundle of semipermeable hollow fiber membranes to continuously equilibrate CO2 in air with a recirculated stream of deionized water. Aqueous carbon dioxide hydrolyzes and dissociates to form the ions H3O+ and HCO3-, thereby increasing the conductivity. The bipolar pulsed method is used to measure the conductivity of the water before and after contact with air. Potential interferences that may also increase the conductivity, such as acids and bases, are removed at the inlet by bicarbonate and bisulfate scrubbers. The detector has been field tested and exhibits a 1/e response time of ∼30 s and precision (RSD) of 0.1%. Field results for measurements at altitudes in the range of 1700−3600 m MSL exhibited an average deviation of 0.16% from values obtained by flask sampling and laboratory measurement usi...
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