Abstract
Abstract. The Henry's law constant is a key property needed to address the multiphase behaviour of organics in the atmosphere. Methods that can reliably predict the values for the vast number of organic compounds of atmospheric interest are therefore required. The effective Henry's law constant H* in air-water systems at 298 K was compiled from literature for 488 organic compounds bearing functional groups of atmospheric relevance. This data set was used to assess the reliability of the HENRYWIN bond contribution method and the SPARC approach for the determination of H*. Moreover, this data set was used to develop GROMHE, a new Structure Activity Relationship (SAR) based on a group contribution approach. These methods estimate logH* with a Root Mean Square Error (RMSE) of 0.38, 0.61, and 0.73 log units for GROMHE, SPARC and HENRYWIN respectively. The results show that for all these methods the reliability of the estimates decreases with increasing solubility. The main differences among these methods lie in H* prediction for compounds with H* greater than 103 M atm−1. For these compounds, the predicted values of logH* using GROMHE are more accurate (RMSE = 0.53) than the estimates from SPARC or HENRYWIN.
Highlights
The oxidation of hydrocarbons emitted in the atmosphere involves complex reaction sequences
This study showed that the bond contribution method developed by Meylan and Howard (1991) and updated in the frame of the HENRYWIN (HWINb) software (Meylan and Howard, 2000) was the most reliable method available
We describe the development of GROMHE and analyse the performance of the three methods considered for this study
Summary
The partitioning of organics between the gas and the aqueous atmospheric phases is usually described in the basis of Henry’s law (e.g., Jacob et al, 1989; Aumont et al, 2000; Herrmann et al, 2000, 2005; Ervens et al, 2003, 2008; Pun et al, 2002; Griffin et al, 2003). A new method, SPARC, has been developed by Hilal et al (2008) This method is based on the product of the activity coefficient in water γw∞ and the vapour pressure P o which are estimated using intermolecular interactions in the pure liquid phase and in solution (e.g., Boethling and Mackay, 2000). Special attention was given to select those compounds with H above 103 Matm−1 which are soluble enough to have significant partitioning in the atmospheric aqueous phase (e.g., Seinfeld and Pandis, 1997; Gelencser and Varga, 2005) This database was used to develop a new SAR: the GROup contribution Method for Henry’s law Estimate (hereafter named GROMHE). We describe the development of GROMHE and analyse the performance of the three methods considered for this study
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