Uncertain Henry's law constants compromise equilibrium partitioning calculations of atmospheric oxidation products Academic Article uri icon

abstract

  • Abstract. Gasparticle partitioning governs the distribution, removal, and transport of organic compounds in the atmosphere and the formation of secondary organic aerosol (SOA). The large variety of atmospheric species and their wide range of properties make predicting this partitioning equilibrium challenging. Here we expand on earlier work and predict gasorganic and gasaqueous phase partitioning coefficients for 3414atmospherically relevant molecules using COSMOtherm, SPARC Performs Automated Reasoning in Chemistry (SPARC), and poly-parameter linear free-energy relationships. The Master Chemical Mechanism generated the structures by oxidizing primary emitted volatile organic compounds. Predictions for gasorganic phase partitioning coefficients (KWIOM/G) by different methods are on average within 1 order of magnitude of each other, irrespective of the numbers of functional groups, except for predictions by COSMOtherm and SPARC for compounds with more than three functional groups, which have a slightly higher discrepancy. Discrepancies between predictions of gasaqueous partitioning (KW/G) are much larger and increase with the number of functional groups in the molecule. In particular, COSMOtherm often predicts much lower KW/G for highly functionalized compounds than the other methods. While the quantum-chemistry-based COSMOtherm accounts for the influence of intra-molecular interactions on conformation, highly functionalized molecules likely fall outside of the applicability domain of the other techniques, which at least in part rely on empirical data for calibration. Further analysis suggests that atmospheric phase distribution calculations are sensitive to the partitioning coefficient estimation method, in particular to the estimated value of KW/G. The large uncertainty in KW/G predictions for highly functionalized organic compounds needs to be resolved to improve the quantitative treatment of SOA formation.

published proceedings

  • ATMOSPHERIC CHEMISTRY AND PHYSICS

altmetric score

  • 3.75

author list (cited authors)

  • Wang, C., Yuan, T., Wood, S. A., Goss, K., Li, J., Ying, Q. i., & Wania, F.

citation count

  • 17

complete list of authors

  • Wang, Chen||Yuan, Tiange||Wood, Stephen A||Goss, Kai-Uwe||Li, Jingyi||Ying, Qi||Wania, Frank

publication date

  • June 2017