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

In the present study condensational droplet growth rates in the binary vapo r system HNO3-H2O were measured over a relatively wide range of vapor activ ities in order to investigate the mass accommodation coefficients in binary vapor mixtures. The measurements on condensational droplet growth rates we re performed in an expansion chamber with a sensitive time of the order of 10 s. Droplet growth rates and the corresponding droplet number concentrati ons 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 n ear atmospheric conditions. The experimental growth curves determined in th e binary vapor system HNO3-H2O are compared to corresponding model calculat ions. Thereby the mass and thermal accommodation coefficients can be determ ined. It can be concluded from the experiments that in binary supersaturate d vapor mixtures of HNO3-H2O the sticking probability for nitric acid molec ules is between 1.0 and 0.3 for the case of the sticking probability for th e water molecules is set to unity. Especially at very low relative humiditi es below 75% very good agreement between experiment and theory can be estab lished 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.