Statistical Analysis of Precipitation Chemistry Measurements over the Eastern United States. Part II: Kriging Analysis of Regional Patterns and Trends

Abstract

The regional patterns and time trends of free acidity and inorganic chemical constituents in precipitation were investigated using a new archive of daily precipitation chemistry measurements for the eastern United States. This archive contains data from three networks during the period 1979 through 1983 and consists of approximately 10 000 precipitation samples. The interpolation method known as Kriging was used to provide objective, unbiased estimates of the regional patterns of the chemical constituents and their time trends. Highest concentrations of hydrogen, sulfate, and nitrate ions occurred along the Ohio River Valley northeastward to New England. Maximum ammonium concentrations occurred in a belt extending from the northern Great Plains eastward across the Great Lakes. Over the period investigated, a small trend toward decreasing acidity and decreasing concentrations of the three main constituents was found. Year-to-year changes were both upward and downward, with values decreasing from 1981 to 1983. More data are required to determine whether the apparent trend is continuing. In contrast, no statistically significant trends were found in the amount of material deposited by precipitation.