Long range transport and deposition of mineral matter as a source for base cations

Mineral dust in the atmosphere is generally alkaline, and is a source of base cations in precipitation. Annual emissions of particles from large combustion plants and industrial processes in Europe is of the order 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. Emissions of dust from the Sahara have been estimated to more than 200 tonnes, with a calcium content of 3–5%. In northern Europe, airborne concentrations of calcium and the concentration of calcium in precipitation are generally consistent with the anthropogenic emissions and their regional 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 precipitation decreases from south to north and from east to west in Europe. Dry deposition of alkaline particles is not well documented, but may be at least as high as the input by precipitation in regions where there are large emissions. There are still large uncertainty gaps with respect to emissions, transport and deposition of calcium-containing particles.