Another Interpretation of the pH Trend in the United States

Abstract

Concern about the apparent increase in the acidity of rainfall from the 1950s to the 1970s prompted reexamination of data from the intermittent, short-term sampling networks that are the basis of the trend estimates. A reassessment of precipitation chemistry data for the mid-1950s reveals excessively high values of calcium and magnesium in comparison with current measurements. The most likely explanation is the severe drought and duststorms that much of the United States experienced in the 1950s. When these excess soil loadings are adjusted within reason to nondrought conditions, newly calculated pH values for this period are not much different from those in recent years. These results suggest that the downward pH trend due to the increase in acid-forming emissions since the mid-1950s is much smaller than previously estimated.