Supplementary material to "A high-accuracy dynamic dilution method for generating reference gas mixtures of carbonyl sulfide at sub-nanomole-per-mole levels for long-term atmospheric observation"

We conducted three experiments described below to examine the factors that affect the dilution accuracy of our dynamic dilution method with respect to carbonyl sulfide (COS).We present the key findings, upon which we based our development of the dynamic dilution method described in the main text.Note that the experiments presented here are referred to as the pilot study in the main text of this study. Experiment-S1We initiated the pilot study by constructing a simple dilution system that blended two gas flows of a parent and a diluent gas; the gas flows were monitored by a Molbloc system and regulated by thermalbased mass flow controllers (MFCs).The experimental system and gases were the same as those described in Sect. 2 in the main manuscript, except that the experimental system did not include the branch exhaust system.To condition the experimental system before starting the experiment, we purged the system for 30 min with the parent and diluent gases at the flow rates that would be set in the dilution experiment.Similarly, after the system purge, one preliminary measurement of the dynamically