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The calibration standards used in the Atmospheric Lifetime Experiment (ALE) for CFCl 3 , CF 2 Cl 2 , CH 3 CCl 3 , and CCl 4 are described. This includes the preparation of the primary standards by static dilution and their propagation and stability for the period 1977–1982. Two independent assessments of the absolute concentrations of the primary standards used to initiate the ALE measurements in 1977–1978 are reported. For consistency in the ALE program the values assigned to the primary standards and subsequent working standards used in the field were not altered during the experiment when results of better estimates of the original concentration values were obtained. Rather, the appropriate factors ξ, by which the ALE mixing ratios for a given species should be multiplied to obtain our best estimate of the current concentration of a given species, are provided.
Rasmussen et al. (Thu,) studied this question.