Universität zu Köln

The formation of aerosols proceeds through nucleation, growth and ageing stages. The understanding of nucleation and droplet growth is essential for handling the more complex atmospheric condensation processes. To achieve this goal, measurements of the nucleation rate of various systems were performed in an expansion chamber (Strey et al. 1994). In this manner nucleation and growth are decoupled by applying a short nucleation pulse (approx. 1 ms) during which the nuclei are formed. The subsequent droplet growth is quantitatively monitored by Mie-scattering. To this end the Mie-maxima and -minima are detected as a function of time and compared to theoretical Mie-scattering calculations for increasing radii. In this fashion a wealth of growth curves depending on supersaturations, number densities of droplets, and temperatures were obtained. Following the approach of Fuchs and Sutugin, theoretical growth-functions using the experimental parameters were calculated, taking into account the depletion of water vapor, the increase of droplet- and system-temperature, temperature-dependent functions of the diffusion-coefficient, surface-tension, liquid-density and latent heat of condensation. The calculated growth-functions and experimental data for 230 K, 240 K and 250 K yield quantitative agreement between theory and experiment. This is remarkable in so far as the theory contains no adjustable parameters and assumes the sticking probability of the vapor molecules to be unity.

English