Precipitation chemistry in Croatia during the period 1981-2006.

The spatial, temporal changes and trends changes in precipitation chemistry in Croatia during the period 1981-2006 were analysed using data from 27 sampling sites. The origins of air masses that arrived over Croatia were evaluated by the sector analysis of two-dimensional back trajectories. The distribution per sector of the volume-weighted concentrations of the main ions (sulfate, nitrate, chloride, ammonium, calcium, magnesium, sodium, and potassium) and the pH were also inspected. The trend in the annual volume-weighted concentrations of the major ions in precipitation and pH was tested using the nonparametric Mann-Kendall test and Sen's slope estimator. The sulfate and nitrate ion concentrations significantly decreased for the majority of sites. The main decline of the sulfate ion concentration occurred after 1990. Changes in the anthropogenic sulfur emission patterns over Europe in the last two decades resulted in different acidity and sulfate ion concentrations related to a particular sector compared to earlier times. In addition, precipitation chemistry in Croatia was also influenced by geographical and climatological diversity. Finally, the war and post-war activities were identified as possible anthropogenic sources of some base cations, i.e., potassium and calcium.