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Abstract
Atmospheric CO2 has been studied since the beginning of the 19th century. After rough evaluations by Dalton (680 ppmv) and Thenard (391 ppmv), an early systematic series of measurements was carried out by the Swiss chemist Nicolas Théodore de Saussure (1830, working in the vicinity of Geneva. He discovered the daily CO2 cycle, with concentrations between 315 and 540 ppmv at noon, and between 321 and 574 ppmv at night.