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Letter

Measurement of the Thermodynamics of the Hydrated Dimer and Trimer of Sulfuric Acid

Supporting Info

D. R. Hanson*^†^‡ and E. R. Lovejoy^§

Atmospheric Chemistry Division, NCAR, Boulder, Colorado 80305, Chemistry Department, Augsburg College, Minneapolis, Minnesota 55454, and Chemical Sciences Division, ESRL/NOAA, Boulder, Colorado 80303

J. Phys. Chem. A, 2006, 110 (31), pp 9525–9528

DOI: 10.1021/jp062844w

Publication Date (Web): July 14, 2006

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

NCAR.

‡

Augsburg College.

ESRL/NOAA.

Abstract

We report measurements of the equilibrium constants, K_p, for the water mediated clustering of two and three sulfuric acid molecules for atmospheric temperatures and relative humidities. Limits for K_p for the formation of the sulfuric acid tetramer and higher clusters as well as the kinetics of small sulfuric acid cluster growth are also presented. These results put strong constraints on the rate of nucleation in the atmosphere via the H₂SO₄/H₂O neutral mechanism. We show that the neutral nucleation of H₂SO₄ and H₂O is slower than ion-induced nucleation of H₂SO₄ and H₂O for most conditions found in the middle and upper troposphere. These laboratory-based upper limits to the nucleation rates are also much lower than the predictions of the liquid drop model/classical nucleation theory.