External quality-assurance programs managed by the U.S. Geological Survey in support of the National Atmospheric Deposition Program/National Trends Network

Abstract

The U.S. Geological Survey, Branch of Quality Systems, operates the external quality-assurance programs for the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). Beginning in 1978, six different programs have been implemented-the intersite-comparison program, the blind-audit program, the sample-handling evaluation program, the field-audit program, the interlaboratorycomparison program, and the collocated-sampler program. Each program was designed to measure error contributed by specific components in the data-collection process. The intersite-comparison program, which was discontinued in 2004, was designed to assess the accuracy and reliability of field pH and specific-conductance measurements made by site operators. The blind-audit and sample-handling evaluation programs, which also were discontinued in 2002 and 2004, respectively, assessed contamination that may result from sampling equipment and routine handling and processing of the wet-deposition samples. The field-audit program assesses the effects of sample handling, processing, and field exposure. The interlaboratorycomparison program evaluates bias and precision of analytical results produced by the contract laboratory for NADP, the Illinois State Water Survey, Central Analytical Laboratory, and compares its performance with the performance of international laboratories. The collocated-sampler program assesses the overall precision of wet-deposition data collected by NADP/NTN. This report documents historical operations and the operating procedures for each of these external quality-assurance programs. USGS quality-assurance information allows NADP/NTN data users to discern between actual environmental trends and inherent measurement variability.

External quality assurance project report for the National Atmospheric Deposition Program’s National Trends Network and Mercury Deposition Network, 2015–16

“…The field audit program uses equipment-rinse samples (bucket samples) paired with corresponding deionized water or synthetic precipitation solutions (bottle samples) to identify changes to chemical concentrations in NTN wet-deposition samples resulting from field exposure of the sample-collection apparatus (Latysh and Wetherbee, 2005;Wetherbee and others, 2010;Wetherbee and Martin, 2016a). After a week without wet deposition, site operators pour 75 percent of the volume of their field audit solution into the sample bucket, and the bucket is sealed with a lid for 24 hours prior to decanting to a clean sample bottle (bucket sample).…”

External quality-assurance results for the National Atmospheric Deposition Program / National Trends Network and Mercury Deposition Network, 2004

“…Many of the samples used in the interlaboratory-comparison program are made from stock solutions prepared by High Purity Standards (HPS), Charleston, South Carolina, which are diluted, bottled, labeled, and shipped by USGS to the participating laboratories. Three sources of samples were used in the interlaboratory-comparison program during 2004: (1) synthetic standard reference samples prepared by HPS and diluted and bottled by USGS; (2) deionized-water samples prepared by USGS; and (3) natural wet-deposition samples collected at NADP/NTN sites and blended by CAL, which were sent to USGS for bottling and shipping to the interlaboratory-comparison laboratories (Latysh and Wetherbee, 2005). Table 3 contains information on the preparation of the solutions made either by HPS, USGS, or CAL, as well as the names of solutions with concentrations traceable to National Institute of Standards and Technology (NIST) reference materials (NISTtraceable samples).…”

“…Samples from NADP/NTN sites are sent to the Illinois State Water Survey, Central Analytical Laboratory (CAL) for analysis. A protocol report providing detailed information on the quality-assurance (QA) procedures and analytical methods is available (Latysh and Wetherbee, 2005).…”

Updated operational protocols for the U.S. Geological Survey Precipitation Chemistry Quality Assurance Project in support of the National Atmospheric Deposition Program

“…The procedures for sample preparation by USGS and sample processing by NTN field-site operators are documented by Latysh and Wetherbee (2005). Throughout 2005-9, nearly every NTN site received a field-audit sample each year.…”

“…A history of the colocated program is summarized in table 3. The protocols for the colocated sampler program for the period 2009-15 were similar to those described in Latysh and Wetherbee (2005). Exceptions include elimination of testing the operating temperatures and electrical resistances of the collectors' precipitation sensors and performing calibration tests of the precipitation gages because data from these tests served no useful purpose.…”