Wet deposition trends of major inorganic ions in Finland based on daily bulk deposition samples

Abstract

Trends in the precipitation-weighted average concentrations and in the deposition of inorganic ions in daily precipitation samples at three Finnish background stations were calculated for a period extending from the seventies to 1988. During the period 1973–1988, S0₄ ²⁻ concentrations in wet deposition at the station in Central Finland decreased by 39% in accordance with the emission decrease of SO₁ in Finland of 50% over the same period, and the 20% decrease in Europe from 1980 to 1988. However, due to the more significant decrease in alkaline ions (80% for Mg²⁺), H⁺ concentrations increased by 30%. At the two southernmost stations, overall concentrations are higher and the decrease of Mg²⁺ and Ca²⁺ is less important, but at the station in southeastern Finland the increase of N0₃ ⁻ relative to NH₄ ⁺ has doubled H⁺ concentrations during the period 1977–1988. Division of the data according to wind direction sectors showed generally decreasing concentrations in the sectors related to Scandinavia, but unchanging or increasing concentrations in the sectors related to eastern Europe. Acid deposition trends were estimated as H⁺, S0₄ ²⁻ - (Ca²⁺ + Mg²⁺), and H⁺ + NH₄ ⁺ - N0₃ ⁺. All these trends showed increasing acid deposition in central Finland and decreasing trends in western Finland. In eastern Finland the trends were opposing due to the increasing N0^{3 +} but decreasing NH₄ ⁻ trends. It is concluded that S0₄ ²⁻ deposition trends do not reflect acid deposition trends, and SO₄ ²⁻ or N0₃ ⁻ deposition do not geographically represent acid deposition.