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Technical Report

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Acid rain, Arkansas, chemistry and wind direction, ion flux, metals, nutrients, rain


Wet and dry fallout at Fayetteville, Arkansas have been collected separately and analyzed since April, 1980. The precipitation-weighted-average pH for two yearly periods of rainfall were 4.72 (6/80-5/81) and 4.75 (6/81-5/82). This corresponds to a concentration of the acid ion, H+, of about 18 parts per billion (ppb). Pure water in equilibrium with the CO2 of the air would have a pH of 5.65 (2.2 ppb of H+). The range of pH during this two year period was 3.86-7.74(140-0 ppb H+) for the rainfall. Aqueous extracts of the dry fallout were always in the 6.75-7.87 pH range, i.e., neutral to slightly alkaline. The slight amount of acidity in the Fayetteville rainfall should be easily neutralized by dry fallout and soil. Ammonium bisulfate, NH4HSO4, is the major acidic chemical in the rains. Sulfur tends to increase in winter months presumably due to the greater use of fossil fuels. Northern rains have the most acidity. Wet and dry fallout add significant amounts of nutrients to the local soils with 25-87% of the total flux being dry fallout. A. major contributor are dust storms which bring in soil from adjacent states. Iron and zinc were the most prevalent heavy metals in the wet fallout. Their concentrations were very low averaging less than 10 ppb for Fe and 15 ppb for Zn. Northernly and southernly rains had the most Fe and Zn and correspond to directions in which there are smelters.

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