Binary nucleation in acid–water systems. I. Methanesulfonic acid–water

Abstract

Experimental measurements of binary nucleation between methanesulfonic acid and water vapor were carried out for relative acidities (Ra), 0.05<Ra<0.65, and relative humidities (Rh), 0.06<Rh<0.65, using a continuous flow mixing-type device. The number concentration of particles leaving the nucleation and growth tube was measured as a function of the initial relative humidity and the relative acidity in the temperature range from 20 to 30 °C. Particle size distributions were also measured and found to vary with the amount of water and acid present. The system was simulated to predict the total number of particles and the total mass of acid in the aerosol phase using a simple integral model and classical binary nucleation theory allowing for the formation of acid–water hydrates in the gas phase. At low particle concentrations, condensation rates did not significantly change the saturation levels and the nucleation rates were estimated from the total number concentration data as functions of Ra, Rh, and temperature. The values of experimental and theoretical nucleation rates differed significantly, with Jexpt/Jtheor changing as a function of temperature from 10−8 to 10−4 as temperature varied from 20 to 30 °C. This work represents the first systematic experimental study of the temperature dependence of binary nucleation.