Significance of water complexes in the atmosphere

Using standard statistical and thermodynamic procedures, we calculate equil ibrium constants for the formation of select, hydrogen-bonded water complex es, namely the water dimer and the cyclic trimer and tetramer, and use them to estimate the atmospheric abundances of these species. We generate water complex altitude profiles (0-30 km) for both a saturated and an unsaturate d atmosphere and discuss the dominant factors influencing our results. In o ur analysis, particular emphasis is given to the significance that water mo nomer concentrations, complex binding energies, hydrogen-bond energies, and entropy have on the calculated abundance profiles. We examine the importan ce of enthalpy and entropy at atmospheric temperatures and show how each co ntributes to our calculated equilibrium constants. By applying a universal 2 degreesC temperature increase throughout the troposphere and lower strato sphere, we are able to model the effect that global warming would have on ( H2O)(n) abundances in a saturated atmosphere. We also illustrate the effect that this thermal variation would have on entropy, enthalpy, and K-p(T) va lues. Based on our results, we assess the atmospheric significance of water dimers and cyclic water complexes. (C) 2001 Elsevier Science Ltd. All righ ts reserved.