On the Temporal Variation of Concentration and Wet Deposition of Sulfate Associated with a Single Event of Frontal Depression

Abstract

Analysis of sequential precipitation samples collected at 9 stations located in the Western Japan were carried out during a period from October to November 1979. Samples were taken by automatic, sequential samplers and measured for pH, conductivity and the concentration of major ions. The source and transport of SO₄^2-in precipitation was discussed on the data obtained.
Temporal variations in the concentration, enrichment factor and wet deposition of SO₄^2- were divided into “initial stage” and “stable equilibrium stage” for convenient consideration. A rapid almost exponential decrease in the concentration of SO₄^2- and other ions except H⁺ was observed during the initial stage when the cyclone passed over the station area. The time constant of this attenuation process was within the rage of 70 to 150 minutes. Wet deposition of the initial stage was relatively small, the stable equilibrium stage was considered to contribute an important role on the total wet deposition of SO₄^2- associated with a single event of frontal depression. SO₄^2-of the stable equilibrium stage was not the oceanic source because the enrichment factor of SO₄^2-was larger than 1. Meteorological analysis suggested that SO₄^2-of the stable equilibrium stage was the anthropogenic sulfur compound, which had been scavenged by precipitation elements in the below cloud layer.