Acidity of Snow and its Reduction by Alkaline Aerosols

Snow crystals scavenge aerosols in the atmosphere during the processes of growth and precipitation. Several kinds of flyash are found in acid snow by scanning electron microscope examination. Flyash particles from coal fired electric power plants in Fairbanks, Alaska, were found to be spherical or irregular in shape with a 0.2 to 50μm diameter, and were rich in calcium, silicon, aluminum and iron. The pH of 35 snow samples in Fairbanks ranged from 5.60 to 7.48. The acid snow was changed to alkaline snow by dry fallout of calcium-rich flyash from the electric power plants, which were using calcium-rich Alaskan coal.Flyash particles from three oil fired heating plants in Hanover, New Hampshire, were spherical and 10 to 80 μm in diameter, with gas escape holes, and were always sulfur rich. The pH values of fresh snow from 44 snowfalls were measured to range from pH 3.96 to 5.45 in Hanover. The mean hydrogen ion concentration was calculated to be 10-448 mol/L for 22 snowfalls in 1980-84, and 10-4 mol/L for 22 snowfalls in 1972-73.