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 cloud-water measurements were performed at two heights above the cloud base. The observed changes in cloud-water concentration were not only induced by dilution or concentration due to an increasing or decreasing liquid water content (LWC), but also by loss or uptake of chemical compounds, and, under appropriate meteorological conditions (downslope flow), by evaporation of small droplets between the two heights. The observed vertical gradients were found to be ion-specific. Higher amounts of total dissolved material were measured at greater distances above the cloud base, e.g. SO42− during most of the time of the monitored cloud events. Thus, vertical gradients may be important for deposition calculations of trace substances onto vegetation via cloud-water interception. In any case, the cloud base is a very important parameter relevant for the cloud chemical studies, because it is of importance for data interpretation.