General Comments:

Scientific significance

This work is novel and important for use in volatile organic compound (VOC) analysis of conifer/plant emissions. Authors make an important point that monoterpenes make up a large portion of plant emissions which then can form secondary organic aerosols. This work highlights a passive sampling headspace adsorption/thermal desorption technique followed by chiral GC-TOFMS analysis.  Six species of conifer clippings were sampled, both nursery and established types.  The sampling included different times of the day and 2 seasons, with 3 or more relicates. Results show good separation, precision and detection of five monoterpenes and their +/- enantiomers.

Strength: This adds to the existing works on chiral monoterpenes by adding the passive sampling with chiral analysis of conifers. Passive sampling is really easy to use and convenient.

Weakness: Authors do not attempt to explain results of the enantiomeric ratios of the emissions.  This may be useful for future research.  Any ideas or hypothesis of why this is?  Compare your active to passive sampling – do you see similar results? Other comparisons were not made. Are there any other works that measure these species?

Uptake rates exist for pinene and limonene on Tenax TA sorbent.  Thus, concentrations could have been calculated in addition to ratios of the enantiomers. This would add to knowledge of how much of these VOCs are emitted, which might be useful to other researchers.

Scientific quality: These experiments were well thought out and conducted.

Presentation quality: The writing style was straightforward and easy to follow.

Specific comments:

Line 88: Please reference your active sampling ATD work.

Line 93: Don’t need diffusive rates since identical is an assumption.  This might be tested in future by measuring the rates.

Line 122: Cut samples of plants instead of living plants sampled. Sampling the living plants in natural environment might have different results. This would be a good experiment to conduct.

Can the time difference of when the cuts were made until analysis matter?

Figures 2-4- I didn’t understand the ABC lettering system in the graph. I did understand capital and lowercase meant statistically insignificant for the monoterpenes, then the species, respectively but I didn’t understand the a-f or A-E designations.  Where these just random to demonstrate the relationships? Please provide abbreviations in the caption or as a footnote. Or consider including in the table summarizing the statistical significance.

Also figures have error bars, please specify if these are 1 standard deviation or something else.

Technical corrections:

Line 167 “was directed to split flow” may sound better.

Table 1:  Last entry: Tenax spelled incorrectly (Tenas)

 The manuscript “Measurement of enantiomer ratios for five monoterpenes from six conifer species by cartridge tube-based passive sampling adsorption/thermal desorption (ps-ATD)" by Wang et al., presents a passive sampling desorption technique used to analyze specific VOCs from conifer/plant emissions. Specifically, five monoterpenes and their +/- enantiomers are analyzed.

The manuscript is well presented and well organized. The main strength of this study is the presentation of a method that can be easy to use delivering sound results. The manuscript is overall worthy of publication after addressing a few minor comments.

What would increase the strength of this study is a comparison with existing methods for the detection of plant-emitted chiral biogenic VOCs. This topic is addressed in Table 1 but a discussion within the main text on how the existing methods compare to the proposed method will further highlight the importance of this study. It looks like other works in literature discuss the measurement of the same species measured here. How do they compare? What would make the suggested method better than what has been already used?

Specific comments:

• Line 45. I wouldn’t just advertise the method precision as “excellent” unless an objective parameter is given so that the reader can see for himself/herself that the precision is indeed very good.
• Line 74. Please give some example of which solvent are commonly used.
• Line 105. Is the altitude agl or asl?
• Lines 106-108. I wonder if these last two sentences should be moved to the next section.
• Line 143. Please indicate which gas was used as carrier.
• Line 177. Should that “during” be eliminated?
• Line 189-190. Please give more details on why was this assumption considered excellent given that it was unverified.