Physicochemical properties of hydrated complexes in the Earth's atmosphere

Theoretical and experimental studies have recently attempted to investigate the role of molecular complexes in the Earth's atmosphere. The extent to which these weakly bound molecular species affect atmospheric chemistry and the climate is ultimately determined by their abundance. In this paper, we discuss the standard statistical procedures that are used in calculating equilibrium constants and dimer abundances. We also highlight the competition that arises between energy and entropy when complexation is considered at atmospherically relevant temperatures. For illustration, the abundance of select hydrated complexes, namely, O-2-H2O, O-3-H2O, H2O-H2O, and NHO3-H2O, are estimated. Using the results of our calculations, we evaluate and compare the physicochemical properties of these hydrated complexes and discuss how monomer concentrations, temperature, and dimer binding energies influence their calculated atmospheric abundances. We further examine the shortcomings of our estimates and include a short analysis outlining the inherent sensitivity of our computational method to discrepancies that exist in the available database for hydrated complexes.