Droplet Formation and Growth in Polluted Fogs

Författare

Göran Frank
Bengt Martinsson
Sven-Inge Cederfelt
Olle Berg
Erik Swietlicki
Manfred Wendish
Brett Yuskiewicz
Jost Heintzenberg
Alfred Wiedensohler
Douglas Orsini
Frank Stratmann
Paolo Laj
Loretta Ricci

Summary, in English

Fog droplet formation and growth related to fog droplet activation were studied in a polluted region. The joint field experiments were carried out at San Pietro Capofiume in northern Italy during November 1994. It was found that the fog droplet number distribution was continuous in the size region 1-47 µm and that for most of the time the fog consisted of unactivated droplets, i.e. the droplets were smaller than the critical diameter for activation according to the Köhler equation. During a few time periods some of the droplets were possibly slightly larger than the critical diameter for activation. The solute concentration in the fog droplets was found to be strongly dependent and decreasing with increasing droplet size. The experimental results were compared with results obtaied using a fog model. Good overall agreement was found between the model and the experimental results, with respect to fog droplet size related to dry residue size, and to fog droplet number distribution. The fog model was also used to study the influence on fog droplet growth of the rate of temperature decrease, the aerosol particle mass load and fog liquid water content. In addition the effect of aging of the fog was also considered.

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