VERTICAL GRADIENTS OF DISSOLVED CHEMICAL-CONSTITUENTS IN EVAPORATING CLOUDS

Vertical gradients in cloud-water composition were investigated during the Ground-based Cloud Experiment at Great Dun Fell(GDF) 1993. The cl oud-water measurements were performed at two heights above the cloud b ase. The observed changes in cloud-water concentration were not only i nduced by dilution or concentration due to an increasing or decreasing liquid water content (LWC), but also by loss or uptake of chemical co mpounds, and, under appropriate meteorological conditions (downslope f low), by evaporation of small droplets between the two heights. The ob served vertical gradients were found to be ion-specific. Higher amount s of total dissolved material were measured at greater distances above the cloud base, e.g. SO42- during most of the time of the monitored c loud events. Thus, vertical gradients may be important for deposition calculations of trace substances onto Vegetation via cloud-water inter ception. In any case, the cloud base is a very important parameter rel evant for the cloud chemical studies, because it is of importance for data interpretation. (C) 1997 Elsevier Science Ltd.