African dust influence on rainwater on the eastern coast of Spain.

In the southeastern coast of Spain bulk deposition was collected, on a daily basis during multiple-day episodes, in order to relate precipitation composition to air mass origins. Samples were analyzed for major ions, in addition to conductivity and alkalinity measurements. The majority of rain had a neutral or alkaline character as a result of neutralization, caused mainly by calcareous soil dust. The occurrence of acidic events or red dust events simultaneously at most stations suggested the influence of transboundary sources. Air mass-trajectories were studied for each of the main events and most of the episodes fell into three main situations: Originating in the Atlantic Ocean, Saharan and Polar continental areas. Chemical rain composition was found to depend on the source area. Meteorological situations with air masses crossing parts of Europe were associated with acidic events. Events coming from the Ocean had a neutral pH and lower concentrations for all species, while those coming from the Sahara have the highest pH values and the highest concentrations for all ions. The relative importance of each source area in southeasterly Mediterranean precipitation was in terms of volume: 62% from Polar Continental, 18% from Saharan, 20% from Oceanic origin. Despite the relative importance of polar continental rainfalls, their acidity is relatively low. The importance of Saharan alkaline rains leads to a net alkaline precipitation in the area.