Na⁺/Cr^- ratios in rain across the USA, 1982–1986

Abstract

Ratios of Na⁺/Cl^-for annual rain collections for 178 sites in the NADP/NTN network across the USA were compared to the same ratio for sea water. 48% of the sites had ratios which were, within experimental error, the same as sea water. 32% of the sites, all in western states, had Na⁺/Cl^- ratios greater than sea water. These higher ratios are attributed to Na⁺ from feldspar and clay aerosols. The remainder (20%) of the sites, with ratios less than sea water are mostly in a contiguous area composed of lower Michigan, lower Wisconsin, eastern Illinois, Indiana, Ohio, Kentucky, West Virginia, northern Virginia, Pennsylvania, New York and Massachusetts. This area coincides with the areas of highest SO^2-₄ and NO^-₃ concentrations in rain and is believed to receive imputs of Cl^- from coal-fired power plants.