LONG-RANGE TRANSPORT AND DEPOSITION OF MINERAL MATTER AS A SOURCE FORBASE CATIONS

Mineral dust in the atmosphere is generally alkaline, and is a source of base cations in precipitation. Annual emissions of particles from l arge combustion plants and industrial processes in Europe is of the or der of 24 million tonnes, and the calcium content may be as high as 1. 4 million tonnes. Emissions from diffuse sources such as agricultural activities, construction and quarrying are much less well known. Emiss ions of dust from the Sahara have been estimated to more than 200 tonn es, with a calcium content of 3-5%. In northern Europe, airborne conce ntrations of calcium and the concentration of calcium in precipitation are generally consistent with the anthropogenic emissions and their r egional distribution. Transport of dust from Sahara is a major source of base cations in precipitation around the Mediterranean Sea, but the influence diminishes further north. The concentration of calcium in p recipitation decreases from south to north and from east to west in Eu rope. Dry deposition of alkaline particles is not well documented, but may be at least as high as the input by precipitation in regions wher e there are large emissions. There are still large uncertainty gaps wi th respect to emissions, transport and deposition of calcium-containin g particles.