Correspondence/Rebuttal pubs.acs.org/est
Comment on “Measured Saturation Vapor Pressures of Phenolic and Nitro-Aromatic Compounds”
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Table 1. Comparison of Subcooled Lipid Vapor Pressures in Pascal for 19 Phenolic and Nitro-Aromatic Compounds As Measured by Bannan et al.,1 As Recommended by Mackay et al.,2 and As Predicted with COSMOtherm.3
n a commendable effort to increase the empirical database on the volatility of multifunctional compounds of atmospheric relevance, Bannan et al.1 measured the saturation vapor pressure of glutarimide, and several substituted benzenes and naphthalenes and compared them with predictions from a number of group contribution methods. The purpose of this correspondence is (1) to raise the possibility that some of the reported data are inaccurate, (2) to report predictions based on a quantum chemistry based method, and (3) to advocate the use of partitioning coefficients instead of vapor pressure for predicting the gas-particle partitioning of atmospherically relevant compounds. (1) Inspection of the reported measured data strongly suggests that the subcooled liquid vapor pressure (pL) of the dihydroxynaphthalenes (Nap(OH)2) reported by Bannan et al.1 are too low. The presented data indicate that the addition of a second hydroxyl-group (OH) to a naphthol on average lowers the reported pL by 5 orders of magnitude (range 3.4 to 6.1 log units). For three of the Naph(OH)2 the reported pL value is labeled an upper limit, which suggests the decrease should be even larger. Recommended values2 for the pL of 22 pairs of aromatic compounds that only differ by a single OH indicate, however, that the decrease in pL upon the addition of an OH is approximately 1.9 ± 0.6 log units (max. 3). It is not plausible that the effect on pL of OH addition to a naphthol is more than double the effect of OH addition to other aromatic compounds, especially because addition of a second OH group would typically lead to a lower effect on pL, due to the possibility of the formation of intramolecular hydrogen bonds. By similar reasoning, the pL reported for 1,3-dinitronaphthalene (1,3-Nap(NO2)2) is likely also too low. It is customary to compare new empirical property data with those reported previously. While this was not done by Bannan et al.,1 reasonable agreement of their pL data with earlier data2 for seven of the studied compounds (Table 1, average absolute difference of 1 log unit, with six out of seven showing a bias to lower values in the new data; likely no statistically significant differences considering the reported uncertainty of ±75%) indicates that not all of the newly reported data are questionable. (2) We used COSMOtherm, commercial software based on quantum chemistry and statistical thermodynamics (COSMOlogic GmbH & Co. KG, Leverkusen, Germany, 2014),3 to predict pL for the 19 compounds studied by Bannan et al.1 (Table 1). COSMOtherm-predicted pL for the substituted benzenes, glutarimide, and the naphthols are within 2 orders of magnitude of the values reported previously2 and by Bannan et al.1 and thus are in better agreement with experimental data than the pL-values predicted for these compounds by group contribution methods. While the concerns about the measured data © XXXX American Chemical Society
compound 1-naphthol 2-naphthol 1,3dihydroxynaphthalene 2,3dihydroxynaphthalene 1,7dihydroxynaphthalene 2,7dihydroxynaphthalene 1,5dihydroxynaphthalene 1-nitronaphthalene 1,3-dinitronaphthalene 2-methyl-1nitronaphthalene o-amino-benzoic acid m-amino-benzoic acid p-amino-benzoic acid m-nitrophenol p-nitrophenol o-nitroaniline m-nitroaniline p-nitroaniline glutarimide
log pL Bannan et al.1
log pL Mackay et al.2
log pL COSMOtherm
−1.10 −0.90 −6.24
−0.30 −0.40
0.14 −0.24 −2.03
−4.26
−1.31
−6.80
−2.09
−6.98
−2.64
−4.70
−1.87
−1.40 −7.45 −1.44 −1.51 −3.89 −2.29 −2.03 −2.40 −1.98 −2.29 −2.03 −1.20
−1.14
−1.42 −2.92 0.27 −0.23
−0.42 −2.21 −0.42 0.02 −1.96 −2.42 −0.75 −2.01 −1.15 −0.98 −4.03 −0.55
(see (1) above) prevents us from evaluating the performance of COSMOtherm for 1,3-Nap(NO2)2 and the Nap(OH)2s, we note that the relationship between pL and the positioning of functional groups is often similar between COSMOtherm-predicted and experimental data, for example, relatively low pL for 2,7Nap(OH)2, 1,3-Nap(OH)2, and 1,3-Nap(NO2)2 contrast with relatively high pL for 2,3-Nap(OH)2 and 1,5Nap(OH)2. Our calculations thus confirm Bannan et al.’s assertion that understanding the effect of functional group positioning “might benefit from quantum scale modeling”. For example, the higher pL for 2,3-Nap(OH)2 is likely due to intramolecular H-bonds between adjacent OH. (3) Despite the promising performance of COSMOtherm in predicting the pL of multifunctional aromatic compounds, we do not advocate the use of COSMOthermpredicted pL in the estimation of partitioning to atmospheric condensed phase for reason laid out in detail previously.4 In particular, we suggest that it is preferable to predict atmospherically relevant partition-
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DOI: 10.1021/acs.est.7b02079 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Correspondence/Rebuttal
Figure 1. Fraction of phenolic and nitro-aromatic compounds in the condensed aerosol phase based on COSMOtherm-predicted equilibrium partitioning coefficients between water insoluble organic matter and the gas phase at 298 K. The dashed lines, dotted line and solid lines represent monocyclic compounds, glutarimide and polycyclic compounds, respectively. Black curved lines represent five condensed mass loadings ranging from 0.01 to 100 μg·m−3. At lower temperatures, the lines for different compounds move to the right of the figure. vapour pressures of phenolic and nitro-aromatic compounds. Environ. Sci. Technol. 2017, 51, 3922−3928. (2) Mackay, D.; Shiu, W. Y.; Ma, K.C.; Lee, S. C. Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals; CRC press, 2006. (3) Klamt, A.; Eckert, F. Cosmo-RS: A novel and efficient method for the a priori prediction of thermophysical data of liquids. Fluid Phase Equilib. 2000, 172, 43−72. (4) Wania, F.; Lei, Y. D.; Wang, C.; Abbatt, J. P. D.; Goss, K.-U. Novel methods for predicting gas-particle partitioning during the formation of secondary organic aerosol. Atmos. Chem. Phys. 2014, 14, 13189−13204. (5) Awonaike, B.; Wang, C.; Goss, K.-U.; Wania, F. Quantifying the equilibrium partitioning of substituted polycyclic aromatic hydrocarbons in aerosols and clouds using COSMOtherm. Environ. Sci. Processes Impacts 2017, 19, 288−299.
ing equilibria directly, rather than estimating pL and the activity coefficient in the condensed phase (or assume the latter to be 1 as Bannan et al.1 have done). When estimating partitioning of the 19 compounds into the organic aerosol phase directly using COSMOtherm,5 we would expect them to be mostly in the gas phase, except for some compounds (Nap(OH)2s, p-nitroaniline) at higher particle loadings (Figure 1). While it is essential to increase the availability of empirical data to improve the prediction of atmospheric phase partitioning, we feel it would be misguided to direct efforts toward making difficult and potentially error-prone pL measurement in order to improve group contribution methods with limited predictive capabilities for multifunctional compounds.
Frank Wania*,† Boluwatife Awonaike† Kai-Uwe Goss‡,§
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† Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario Canada M1C 1A4 ‡ Department of Analytical Environmental Chemistry, Centre for Environmental Research UFZ Leipzig-Halle, Permoserstraße 15, Leipzig, D-04318, Germany § Institute of Chemistry, University of Halle-Wittenberg, Kurt-Mothes-Straße 2, Halle, D-06120, Germany
AUTHOR INFORMATION
Corresponding Author
*Phone: +1 416 287 7225; e-mail:
[email protected]. ORCID
Frank Wania: 0000-0003-3836-0901 Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Bannan, T. J.; Booth, A. M.; Jones, B. T.; O’Meara, S.; Barley, M. H.; Riipinen, I.; Percival, C. J.; Topping, D. O. Measured saturation B
DOI: 10.1021/acs.est.7b02079 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
