Structure-activity relationships to estimate the effective Henry's law constants of organics of atmospheric interest

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.