Scavenging Ratios in an Urban Area in the Spanish Basque Country

Abstract

For a period of six years (1995–2000) the scavenging ratio, which is the ratio of a pollutant's concentration in water to its concentration in air, collected at an urban site in the Spanish Basque Country was studied. The aerosol is characterized by SO₄ ²⁻ and NO₃− with 1.79 and 1.61 μg m⁻³, respectively. Greater fractions of SO₄ ²⁻, NO₃−, and NH₄+ ions were present in the fine particle range, while greater fractions of other ions appeared in the coarse range. The most important species found in the precipitation is SO₄ ²⁻ with 3.0 mg l⁻¹. NO₃−, Ca²⁺, and Cl⁻ are the second most important ions. The volume-weighted mean concentration of H⁺ is 4.6 μg l⁻¹ (pH = 5.3). The concentration of all analyzed ions (except H⁺) decreases throughout the rain event, showing the washout phenomenon of the rainwater. The scavenging ratio for the anthropogenic ions NO₃−, SO₄ ²⁻, NH₄+, and K⁺ is lower than the scavenging ratio for the marine-terrigenous ions, Cl⁻, Na⁺, and Ca²⁺.

Acknowledgments

This work is a part of the “Cuantificación y estudio del depósito contaminante atmosférico en la CAPV y sus posibles efectos sobre las poblaciones de Pinus radiataD. Don” programme. The Basque Government sponsors this program.