Experimental study of sticking probabilities for condensation of nitric acid - water vapor mixtures

In the present study condensational droplet growth rates in the binary vapor system HNO3-H2O were measured over a relatively wide range of vapor activities in order to investigate the mass accommodation coefficients in binary vapor mixtures. The measurements on condensational droplet growth rates were performed in an expansion chamber with a sensitive time of the order of 10 s. Droplet growth rates and the corresponding droplet number concentrations were determined by the Constant angle mie scattering (CAMS) method. In the present study the droplet radii cover a range from 0.5 to about 4 mum. The experiments were performed at constant temperature and total pressure near atmospheric conditions. The experimental growth curves determined in the binary vapor system HNO3-H2O are compared to corresponding model calculations. Thereby the mass and thermal accommodation coefficients can be determined. It can be concluded from the experiments that in binary supersaturated vapor mixtures of HNO3-H2O the sticking probability for nitric acid molecules is between 1.0 and 0.3 for the case of the sticking probability for the water molecules is set to unity. Especially at very low relative humidities below 75% very good agreement between experiment and theory can be established when the sticking probability of water as well as of nitric acid is regarded to be unity. (C) 2001 Elsevier Science Ltd. All rights reserved.