Data for the U.S. Geological Survey Precipitation Chemistry Quality Assurance Project for the National Atmospheric Deposition Program, 1978–2017

Publication Date

2020-12-11

Start Date

1978-01-01

Wetherbee, G.A., 2020, Data for the U.S. Geological Survey Precipitation Chemistry Quality Assurance Project for the National Atmospheric Deposition Program, 1978–2017: U.S. Geological Survey data release, https://doi.org/10.5066/P94RC4GD.

The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) was initiated in 1978 by the Association of State Agricultural Experiment Stations to monitor long-term atmospheric chemistry and the effects pollutants have on aquatic and terrestrial systems. As of fall 2017, precipitation was being collected at approximately 265 NTN sites and 100 MDN sites in the United States, including Puerto Rico and U.S.Virgin Islands, and additionally Argentina and Canada. Beginning in 1996, The NADP/Mercury Deposition Network (MDN) has monitored mercury (Hg) in precipitation in the United States including Puerto Rico, plus Canada and formerly in Mexico. The U.S. Geological Survey PCQA began quality-assurance monitoring for NADP/NTN in 1978 and for NADP/MDN in 2004. The quality-assurance programs assess and document the quality of wet-deposition data for NADP/NTN and NADP/MDN. For nearly 40 years, the NADP Central Analytical Laboratory (CAL) was located at the University of Illiniois, Champaign/Urbana, Illinois. In 2018, the CAL moved to the University of Wisconsin, Madison, Wisconsin. The CAL analyzes all weekly precipitation samples collected by NADP/NTN. From 1996 to date (June 2018), the Mercury Analytical Laboratory (HAL) for the NADP/MDN has been operated by Eurofins Frontier Global Sciences, Inc., located in Bothell, Wash. The PCQA programs are continually evolving as described in the USGS reports: 1.USGS Water-Resources Investigations Report 90-4029, "Programs and Analytical Methods for the U.S. Geological Survey Acid Rain Quality-Assurance Project (See and others, 1990); 2.USGS Open-File Report 2005-1024, External Quality-Assurance Programs Managed by the U.S. Geological Survey in Support of the National Atmospheric Deposition Program/National Trends Network (Latysh and Wetherbee, 2005); 3.USGS Open-File Report 2007-1170, External Quality Assurance Programs Managed by the U.S. Geological Survey in Support of the National Atmospheric Deposition Program/Mercury Deposition Network (Latysh and Wetherbee, 2007); and 4. USGS Open-File Report 2016-1213, Updated Operational Protocols for the U.S. Geological Survey Precipitation Chemistry Quality Assurance Project in Support of the National Atmospheric Deposition Program (Wetherbee and Martin, 2016). Several programs have been implemented by the PCQA to measure variability and bias contributed by specific components in NADP data-collection processes. The programs independently address field- and laboratory-oriented components and the overall variability of NADP measurements of wet-deposition chemistry and precipitation depth. Existing programs evaluate the variability and bias of chemical analyses from NADP laboratories and sample stability and contamination from field exposure. These programs are: 1. Interlaboratory-comparison programs for NTN Central Analytical Laboratory and MDN Mercury Analytical Laboratory to compare their performance with other international laboratories. 2. NTN Field Audit and MDN System Blank programs to evaluate sample contamination and stability. 3. A Colocated Sampler program evaluates the overall variability of NTN measurements using identical precipitation gages and collectors. The Colocated Sampler program has also been used to evaluate bias between dissimilar precipitation gages and sample collectors. Colocated studies are conducted at NADP sites located in various precipitation regimes across the USA. Discontinued programs include: 4. NTN and MDN Blind-Audit programs disguised quality-control samples as actual field samples and submitted them to the laboratories to check analytical variability and bias. 5. A Sample Handling Evaluation program was operated to determine the effects of sample processing on variability and bias in NADP chemistry results. 6. An Intersite program evaluated the quality of field measurements of pH and specific conductance of the rainwater samples. This program was discontinued when NADP discontinued field measurements of pH and specific conductance. Evaluation and interpretation of the PCQA program results gives users of NADP data the assurance that measurements are representative of environmental conditions. The programs test the NADP measurements to ensure that the data are of sufficient quality for use in identification and quantification of spatial and temporal trends in atmospheric wet-deposition chemistry. These data are for a quality-control testing project. As such, most of these data are NOT representative measurements of the environment and should not be used as such, except for the Colocated Sampler data, which are true environmental measurements.

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