Programs and analytical methods for the US Geological Survey Acid Rain Quality-Assurance Project

Abstract

The US Geological Survey operates four programs to provide external quality-assurance of wet deposition monitoring by the National Atmospheric Deposition Program and the National Trends Network. An intersite-comparison program assesses the precision and bias of onsite determinations of pH and specific conductance made by site operators. A blind-audit program is used to assess the effect of routine sample-handling procedures and transportation on the precision and bias of wet-deposition data. An interlaboratory comparison program is used to assess analytical results from three or more laboratories, which routinely analyze wet-deposition samples from the major North American networks, to determine if comparability exists between laboratory analytical results and to provide estimates of the analytical precision of each laboratory. A collocated sampler program is used to estimate the precision of wet/dry precipitation sampling throughout the National Atmospheric deposition Program and the Nation Trends Network to assess the variability of varying spatial arrays and to evaluate the impact of violations of specific site criteria. This report documents the procedures and analytical methods used in these four quality-assurance programs.