General Comments

Tsogt et al. describe the development and evaluation of primary gas standard mixtures of acetonitrile at µmol mol^-1 and nmol mol^-1 levels in different cylinder passivation treatments in support of global monitoring efforts within the WMO GAW program. The work is important and novel and the experimental work appears to be of good quality. I recommend publishing after some minor errors have been address as outlined below:

Minor comments

In the methods section (Page 3, lines 80-87) there appears to be some errors in the assignment of references in this paragraph as follows:

1. Page 3, line 81: the text “…and the modified gravimetric method (Brewer, 2011).” Brewer 2011 is not correct here and this should actually be Brewer et al., 2019 (Anal. Chem 91(8), 5310-5315).
2. Page 3, line 81: the text “…known to be stable in aluminium cylinders (Rhoderick, 2013, Brewer, 2019)….”, the reference to Brewer, 2019 is not correct here. An additional reference that should be included here instead is Rhoderick et al., 2019 (doi: 1525/elementa.366) as this paper demonstrates stability for hexane in the nmol mol^-1 range in the Experis cylinder being used in this study.

Page 3, line 23: It was not clear to me what the reference was that is referred to here? It looks like from the plots that one mixture has been chosen as the reference and the other results have been normalised to that selected mixture. This was not clear and the choice for the reference was not clear. Some specific text needs to be included to address this.

Technical corrections

Figure 4: I suggest removing the ACN and hexane labels from the figure replacing them with A and B labels for the two panels and refer to each in the caption with reference to hexane or ACN.

There is an inconsistent use of nmol mol^-1 (also µmol mol^-1) and nmol/mol (also µmol/mol) throughout the paper, the mol mol^-1 is preferred but usage should be consistent throughout. Currently both formats are used in the paper.