Atmospheric deposition in European forests in 2018

Studying the effects of atmospheric pollution to forest ecosystems requires an evaluation of air quality and of the amount of pollutants carried to the forests by atmospheric deposition. Pollutant flux towards ecosystems through deposition mainly follows two pathways: wet deposition of compounds dissolved in rain, snow, sleet or similar, and dry deposition of particulate matter through gravity or adsorption on forest canopy for example. Pollutant deposition shows a relatively high local variability, related to the distribution of pollutant sources and the local topography, and in-situ measurement is needed to obtain accurate evaluations and to validate model estimates. In 2018, the chemical composition of atmospheric deposition was measured in 293 ICP Forests Level II permanent plots throughout Europe. In this report, we focus on acidifying, buffering, and eutrophying compounds. High values of nitrate deposition were mainly found in central Europe (Germany, Denmark, Belgium and eastern Austria), while for ammonium they were also found in northern Italy and Poland. The area of high deposition is smaller for sulphate, including some plots in Germany, Greece and Poland. High sulphate values are also measured in Belgium, but they are partially due to deposition of marine aerosol, and they are less evident after sea-salt correction. Calcium and magnesium deposition can buffer the acidifying effect of atmospheric deposition. High values of calcium deposition are reported in southern Europe, mainly related to the deposition of Saharan dust, and in eastern Europe. The correction for the marine contribution of calcium matters mainly for sites in central Europe and in Spain. On the contrary, in the case of magnesium, the distribution of the highest values is markedly reduced by the sea salt correction.