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

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 https://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit https://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 of chemical constituents in water are given in either milligrams per liter (mg/L), micrograms per liter (µg/L) or nanograms per liter (ng/L).α, alpha, is the maximum probability of incorrect rejection of the null hypothesis. The NADP Central Analytical Laboratory produced interlaboratory comparison results with low bias and variability compared to other domestic and international laboratories that support atmospheric deposition monitoring. Significant absolute bias above the magnitudes of the detection limits was observed for nitrate and sulfate concentrations, but no analyte determinations exceeded the detection limits for blanks.Colocated sampler program results from dissimilar colocated collectors indicate that the retrofit of the National Trends Network with N-CON Systems Company, Inc. precipitation collectors could cause substantial shifts in NADP annual deposition (concentration multiplied by depth) values. Median weekly relative percent differences for analyte concentrations ranged from -4 to +76 percent for cations, from 5 to 6 percent for ammonium, from +14 to +25 percent for anions, and from -21 to +8 percent for hydrogen ion contamination. By comparison, weekly absolute concentration differences for paired identical N-CON Systems Company, Inc., collectors ranged from 4-22 percent for cations; 2-9 percent for anions; 4-5 percent for ammonium; and 13-14 percent for hydrogen ion contamination. The N-CON Systems Company, Inc. collector caught more precipitation than the Aerochem Metrics Model 301 collector (ACM) at the WA99/99WA sites, but it typically caught slightly less precipitation than the ACM at ND11/11ND, sites which receive more wind and snow than WA99/99WA. Paired, identical OTT Pluvio-2 and ETI Noah IV precipitation gages were operated at the same sites. Median absolute percent differences for daily measured precipitation depths ranged from 0 to 7 percent. Annual absolute differences ranged from 0.08 percent (ETI Noah IV precipitation gages) to 11 percent (OTT Pluvio-2 precipitation gages).The Mercury Deposition Network programs include the system blank program and an interlaboratory comparison program. System blank results indicate that maximum total mercury contamination concentrations in s...

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

“…As shown for results in previous years, results of blank analyses indicate that HAL Hg contamination during the study period was low (Wetherbee and Martin, 2016b). Therefore, most Hg contamination in MDN samples, which was estimated using the system blanks, was likely introduced in the field.…”

“…This method uses order statistics, which are based on ranking the data from lowest to highest and applying binomial probability to determine the UCL. More detail is provided in Wetherbee and Martin (2016b).…”

Atmospheric mercury deposition over the land surfaces and the associated uncertainties in observations and simulations: a critical review

“…GMOS reported the ongoing precision recovery (OPR) for every 12 samples to be generally within 93 %-109 % . The relative percentage difference (RPD) for MDN precipitation Hg analysis is generally within 10 % according to inter-laboratory comparisons (Wetherbee and Martin, 2018). For individual studies (Fu et al, 2010a;Huang et al, 2015;Zhao et al, 2018), the RSD is also generally less than 10 %.…”