Uptake of Gas-Phase Species by 1-Octanol. 2. Uptake of Hydrogen Halides and Acetic Acid as a Function of Relative Humidity and Temperature

Abstract

With use of a droplet train apparatus, the mass accommodation coefficients (α) of gas-phase HCl, HBr, HI, and CH3COOH were measured for 1-octanol to probe the nature of the hydrophobic organic surface as a function of relative humidity and temperature (263−283 K). In the absence of water vapor, α for both HBr(g) and HI(g) is unity, independent of temperature. The mass accommodation coefficients for acetic acid and HCl are smaller, about 0.3 for acetic acid and 0.01 for HCl at 273 K, displaying negative temperature dependence. The value of α for acetic acid is independent of relative humidity. However, values of α for HBr, HI, and HCl change dramatically as a function of relative humidity. As the relative humidity increases, the α values for HBr and HI decrease, and α for HCl increases. At a relative humidity of about 50%, α for all three species converges to that on pure water. A model is proposed to explain these unexpected results.