the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Optimizing Iodide-Adduct CIMS Quantitative Method for Toluene Oxidation Intermediates: Experimental Insights into Functional Group Differences
Abstract. Iodide-Adduct time-of-flight chemical ionization mass spectrometry (I-CIMS) has been developed as a powerful tool for detecting the oxidation products of volatile organic compounds. However, the accurate quantification of species that do not have generic standards remains a challenge for I-CIMS application. To accurately quantify aromatic hydrocarbon oxidation intermediates, both quantitative and semi-quantitative methods for I-CIMS were established for intermediate species. The direct quantitative experimental results reveal a correlation between sensitivity to iodide addition and the number of polar functional groups (keto groups, hydroxyl groups, and acid groups) present in the species. Leveraging the selectivity of I-CIMS for species with diverse functional groups, this study established semi-quantitative equations for four distinct categories: monophenols, monoacids, polyphenol or diacid species, and species with multiple functional groups. The proposed classification method offers a pathway to enhance the accuracy of the semi-quantitative approach, achieving an improvement in R2 values from 0.50 to beyond 0.88. Overall, the categorized semi-quantitative method was utilized to quantify intermediates formed during the oxidation of toluene under both NO-free and NO-applied conditions, revealing the differential variations in oxidation products with varying levels of NOx concentration.
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RC1: 'Comment on egusphere-2024-1203', Anonymous Referee #1, 15 May 2024
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In this manuscript, the authors present an attempt to quantify toluene oxidation intermediates by establishing quantitative and semi-quantitative calibration methods for I-CIMS. Specifically, the authors established semi-quantitative equations for four distinct categories: monophenols, monoacids, polyphenol or diacid species, and species with multiple functional groups. This classification method enhances the accuracy of the semi-quantitative approach (R2 from ~0.50 to >0.88). Overall, the research goal of this manuscript is novel and has practical atmospheric significance. The description of the calibration methods and experimental results is logical and comprehensive. After the authors address the minor comments below, the manuscript can be published in AMT.
1. Line 42, “H3O+ ions are used for the detection of VOCs”. This description here is not accurate. Conventional PTR has the ability to detect some I/SVOCs, although not many species. The newly developed Vocus or Fusion PTR can detect more I/SVOCs, some of which are oxygenated compounds (e.g., Atmos. Meas. Tech. 2019, 2403-2421).
2. Lines 53-76, some key references are missing when introducing the calibration method of CIMS and its research progress. For example, Li et al. (Environ. Sci. Technol. 2021, 12841-12851) used 22 organic standards to calibrate I-CIMS and reduced the uncertainty in total organic carbon concentrations to ~20%-35% when combining the voltage scanning approach.
3. Line 172, “humidity” should be “relative humidity”.
4. Section 3.1, it would be more straightforward to list the sensitivities in a table, probably in Table S1.
5. Line 230, the sections and figures in the SI should be presented in order in the manuscript.
6. Figure 2, it is difficult to match the data points to compound names. Adding some arrows may help.
7. Lines 363-370, could the authors show the time series of C7H8O4, C7H10O4, C7H10O5, C4H4O3, and C5H6O3 separately somewhere in the SI? It would be helpful to see the ratio of C5H6O3 to C4H4O3 as well.
8. Lines 401-403, there is no need to repeat these numbers in the conclusion.
9. Check the capitalization of the first letter. Some examples: Line 60, “Discovered”; Line 149, “Computational”; Line 213, “2,6-Xylenol and Texanol”; Compound names in Figure 2; Line 288, “Salicylic acid, Citric acid”.
Citation: https://doi.org/10.5194/egusphere-2024-1203-RC1
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