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

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://store.usgs.gov/.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Supplemental InformationSpecific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25°C). Concentrations AbstractThe U.S. Geological Survey Branch of Quality Systems operates the Precipitation Chemistry Quality Assurance Project (PCQA) for the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) and National Atmospheric Deposition Program/Mercury Deposition Network (NADP/MDN). Since 1978, various programs have been implemented by the PCQA to estimate data variability and bias contributed by changing protocols, equipment, and sample submission schemes within NADP networks. These programs independently measure the field and laboratory components which contribute to the overall variability of NADP wet-deposition chemistry and precipitation depth measurements. The PCQA evaluates the quality of analyte-specific chemical analyses from the two, currently (2016) contracted NADP laboratories, Central Analytical Laboratory and Mercury Analytical Laboratory, by comparing laboratory performance among participating national and international laboratories. Sample contamination and stability are evaluated for NTN and MDN by using externally field-processed blank samples provided by the Branch of Quality Systems. A colocated sampler program evaluates the overall variability of NTN measurements and bias between dissimilar precipitation gages and sample collectors.This report documents historical PCQA operations and general procedures for each of the external quality-assurance programs from 2007 to 2016.

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

“…The variability of the results from the new sample collectors was assessed using the colocated sampler program during 2016. Detailed information on USGS QA procedures and analytical methods for the NTN and MDN is available in Wetherbee (2005, 2007) and Wetherbee and Martin (2016a).…”

“…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).…”

“…The three types of samples used in the interlaboratory comparison program included (1) synthetic standard reference samples prepared by PCQA, which are traceable to National Institute of Standards and Technology (NIST) reference materials (NIST-traceable samples); (2) de-ionized water blank samples prepared by PCQA; and (3) natural wet-deposition samples collected at NTN sites, blended by CAL, and sent to PCQA for shipping to the laboratories as blind samples (Wetherbee and Martin, 2016a). Synthetic precipitation samples used in the interlaboratory comparison program were made from stock solutions prepared by High Purity Standards, Charleston, South Carolina.…”

“…Protocols for the PCQA external QA programs for MDN are described in detail by Wetherbee and Martin (2016a). The MDN system blank program is similar to the NTN field audit program, whereby the effects of onsite environmental exposure, handling, and shipping on sample contamination are evaluated.…”

External quality assurance project report for the National Atmospheric Deposition Program’s National Trends Network and Mercury Deposition Network, 2017–18

“…The variability of NTN results was assessed using the colocated sampler program during water years 2017-18. Detailed information on USGS QA procedures and analytical methods for the NTN and MDN is available in Wetherbee (2005, 2007) and Wetherbee and Martin (2016a).…”