LeRoy J. Schroder

The precision of wet atmospheric deposition data from national atmospheric deposition program/national trends network sites determined with collocated samplers

Abstract A collocated, wet-deposition sampler program has been operated since October 1988 by the U.S. Geological Survey to estimate the overall sampling precision of wet atmospheric deposition data collected at selected sites in the National Atmospheric Deposition Program and National Trends Network (NADP/NTN). A duplicate set of wet-deposition sampling instruments was installed adjacent to existing sampling instruments at four different NADP/NTN sites for each year of the study. Wet-deposition samples from collocated sites were collected and analysed using standard NADP/NTN procedures. Laboratory analyses included determinations of pH, specific conductance, and concentrations of major cations and anions. The estimates of precision included all variability in the data-collection system, from the point of sample collection through storage in the NADP, /NTN database. Sampling precision was determined from the absolute value of differences in the analytical results for the paired samples in terms of median relative and absolute difference. The median relative difference for Mg 2+ , Na + , K 4 + and NH concentration and deposition was quite variable between sites and exceeded 10% at most sites. Relative error for analytes whose concentrations typically approached laboratory method detection limits were greater than for analytes that did not typically approach detection limits. The median relative difference for S0 4 2− and NO 3 − concentration, specific conductance, and sample volume at all sites was less than 7%. Precision for H + concentration and deposition ranged from less than 10% at sites with typically high levels of H + concentration to greater than 30% at sites with low H + concentration. Median difference for analyte concentration and deposition was typically 1.5-2-times greater for samples collected during the winter than during other seasons at two northern sites. Likewise, the median relative difference in sample volume for winter samples was more than double the annual median relative difference at the two northern sites. Bias accounted for less than 25% of the collocated variability in analyte concentration and deposition from weekly collocated precipitation samples at most sites.

Evaluation of methods for preservation of water samples for nutrient analysis

Mercuric ion, sulfuric acid, and chloroform were examined as preservatives for nitrogen and phosphorus species in water samples containing biologically active microorganisms. Chilling at 4°C without addition of a chemical preservative also was examined. Chilling alone at 4°C was an adequate preservation technique for 8‐day storage for the water samples used in this study. However, for samples analyzed after 16‐day storage, the addition of 40 milligrams per liter of mercuric ion plus chilling at 4°C, appeared to be the preservation technique of choice. Neither chloroform nor sulfuric acid, coupled with chilling, were adequate as preservation techniques for all analytes determined during the 16‐day study period.

Atmospheric deposition sampler intercomparison

AbstractTwo wet/dry atmospheric deposition sampler types were compared for 1 yr. The resistance required to open each of ten collectors was determined. Additionally, the opening and closing history of each sampler was recorded using a microdatalogger with a resolution of 1 min. The frequency distribution of amount of time that a collector was open was used to evaluate the comparability of opening and closing of each collector. Weekly amounts of rainfall for each of the collectors was used to determine the efficiency of collection as compared to a Belfort 5–780 weighing rain gauge. The performance of a collector as determined by the efficiency of collection and also by the distribution of frequencies of times that a sampler was exposed to precipitation were statistically different for the different sampler configurations. Disclaimer. Publication, does not signify that the contents necessarily reflect the views and policies of Department of the Army and the US Military Academy, nor does mention of trade names or commerical products constitute endorsement or recommendation for use. Not subject to copyright restrictions, work of US Government.

Comparison of daily and weekly precipitation sampling efficiences using automatic collectors

Precipitation samples were collected for approximately 90 daily and 50 weekly sampling periods at Finley Farm, near Raleigh, North Carolina from August 1981 through October 1982. Ten wet-deposition samplers (AEROCHEM METRICS MODEL 301) were used; 4 samplers were operated for daily sampling, and 6 samplers were operated for weekly-sampling periods. This design was used to determine if. (1) collection efficiences of precipitation are affected by small distances between the Universal (Belfort) precipitation gage and collector; (2) measurable evaporation loss occurs and (3) pH and specific conductance of precipitation vary significantly within small distances.Average collection efficiencies were 97% for weekly sampling periods compared with the rain gage. Collection efficiencies were examined by seasons and precipitation volume. Neither factor significantly affected collection efficiency. No evaporation loss was found by comparing daily sampling to weekly sampling at the collection site, which was classified as a subtropical climate. Correlation coefficients for pH and specific conductance of daily samples and weekly samples ranged from 0.83 to 0.99.

Variation in precipitation quality during a 40‐hour snowstorm in an Urban Environment — Denver, Colorado

Seventeen precipitation samples were collected during a 40‐hour snowstorm in the northwestern part of the Denver, Colorado, metropolitan area. Maximum concentrations of barium, calcium, cadmium, chloride, iron, potassium, magnesium, sodium, nitrate, phosphate and sulfate occurred during the initial three hours of the storm. The maximum copper concentrations occurred nearly six hours after the storm began, the maximum strontium concentration occurred 25 hours after the storm began, and the maximum zinc concentration occurred 12 hours after the storm began. Concentrations of beryllium, cobalt, lithium and vanadium were less than the analytical detection limits during the entire storm. Lowest pH values were determined in samples collected during or immediately after periods of normal, maximum automobile traffic.

Evaluation of metal ion absorptive characteristics of three types of plastic sample bags used for precipitation sampling

Abstract Simulated precipitation samples containing 16 metal ions were prepared at 4 pH values. Absorptive characteristics of polypropylene, polyethylene, and polyester/polyolefin sacks were evaluated at pH 3.5, 4.0, 4.5, and 5.0. Simulated precipitation was in contact with the sacks for 17 days, and subsamples were removed for chemical analysis at 3, 7, 10, 14, and 17 days after initial contact. All three types of plastic sacks absorbed Fe throughout the entire pH range. Polypropylene and polyethylene absorbed Pb throughout the entire pH range; polyester/polyolefin sacks absorbed Pb at pH 4.0 or greater. All plastic sacks also absorbed Cu, Mo, and V at pH 4.5 and 5.0. Leaching the plastic sacks with 0.7 percent HNO3 did not result in 100 percent recovery of Cu, Fe, Pb, and V. These sacks would be suitable collection vessels for Ba, Be, Ca, Cd, Co, Li, Mg, Mn, Na, Sr and Zn in precipitation through the pH range of 3.5 to 5.0.

A quality-assurance assessment for constituents reported by the national atmospheric deposition program and the national trends network

Abstract A continuing quality-assurance program has been operated by the U.S. Geological Survey to evaluate any bias introduced by routine handling, shipping, and laboratory analyses of wet-deposition samples collected in the National Atmospheric Deposition Program (NADP) and National Trends Network (NTN). Blind-audit samples having a variety of constituent concentrations and values were selected. Only blind-audit samples with constituent concentrations and values less than the 95th-percentile concentration for natural wet-deposition samples were included in the analysis. Of the major ions, there was a significant increase of Ca 2+ , Mg 2+ , Na 2+ , K + , SO 4 2− and Cl −1 in samples handled according to standard protocols and shipped in NADP/NTN sample-collection buckets. For 1979–1987, graphs of smoothed data showing the estimated contamination in blind-audit samples indicate a decrease in the median concentration and ranges of Ca 2+ , Mg 2+ and SO 4 2− contamination of blind-audit samples shipped in sample-collection buckets. Part of the contamination detected in blind-audit samples can be attributed to contact with the sample-collection bucket and lid; however, additional sources also seem to contaminate the blind-audit sample. Apparent decreases in the magnitude and range of sample contamination may be caused by differences in sample-collection bucket- and lid-washing procedures by the NADP/NTN Central Analytical Laboratory. Although the degree of bias is minimal for most constituents, summaries of the NADP/NTN data base may contain overestimates of Ca 2+ , Mg 2+ , Na − , K + and SO 4 2− and Cl − concentrations, and underestimates of H + concentrations.

Recovery of several volatile organic compounds from simulated water samples: Effect of transport and storage

Solutions containing volatile organic compounds were prepared in organic-free water and 2% methanol and submitted to two US Geological Survey laboratories. Data from the determination of volatile compounds in these samples were compared to analytical data for the same volatile compounds that had been kept in solutions 100 times more concentrated until immediately before analysis; there was no statistically significant difference in the analytical recoveries. Addition of 2% methanol to the storage containers hindered the recovery of bromomethane and vinyl chloride. Methanol addition did not enhance sample stability. Further, there was no statistically significant difference in results from the two laboratories, and the recovery efficiency was more than 80% in more than half of the determinations made. In a subsequent study, six of eight volatile compounds showed no significant loss of recovery of 34 days. 19 references, 3 figures, 2 tables.

The stability of hydrogen ion and specific conductance in filtered wet-deposition samples stored at ambient temperatures

Separate experiments by the U.S. Geological Survey (USGS) and the Illinois State Water Survey Central Analytical Laboratory (CAL) independently assessed the stability of hydrogen ion and specific conductance in filtered wet-deposition samples stored at ambient temperatures. The USGS experiment represented a test of sample stability under a diverse range of conditions, whereas the CAL experiment was a controlled test of sample stability. In the experiment by the USGS, a statistically significant (α=0.05) relation between [H+] and time was found for the composited filtered, natural, wet-deposition solution when all reported values are included in the analysis. However, if two outlying pH values most likely representing measurement error are excluded from the analysis, the change in [H+] over time was not statistically significant. In the experiment by the CAL, randomly selected samples were reanalyzed between July 1984 and February 1991. The original analysis and reanalysis pairs revealed that [H+] differences, although very small, were statistically different from zero, whereas specific-conductance differences were not. Nevertheless, the results of the CAL reanalysis project indicate there appears to be no consistent, chemically significant degradation in sample integrity with regard to [H+] and specific conductance while samples are stored at room temperature at the CAL. Based on the results of the CAL and USGS studies, short-term (45–60 day) stability of [H+] and specific conductance in natural filtered wet-deposition samples that are shipped and stored unchilled at ambient temperatures was satisfactory.

Validation of an automated fluorescein method for determining bromide in water

Abstract Surface, atmospheric precipitation and deionized water samples were spiked with μg l−1 concentrations of bromide, and the solutions stored in polyethylene and polytetrafluoroethylene bottles. Bromide was determined periodically for 30 days. Automated fluorescein and ion chromatography methods were used to determine bromide in these prepared samples. Analysis of the data by the paired t-test indicates that the two methods are not significantly different at a probability of 95% for samples containing from 0.015 to 0.5 mg l−1 of bromide. The correlation coefficient for the same sets of paired data is 0.9987. Recovery data, except for the surface water samples to which 0.005 mg l−1 of bromide was added, range from 89 to 112%. There appears to be no loss of bromide from solution in either type of container.