<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>L.J. Schroder</dc:contributor>
  <dc:contributor>T. C. Willoughby</dc:contributor>
  <dc:creator>R.B. See</dc:creator>
  <dc:date>1989</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;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&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, Mg&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, Na&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, K&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;, SO&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;and Cl&lt;/span&gt;&lt;sup&gt;−1&lt;/sup&gt;&lt;span&gt;&amp;nbsp;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&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, Mg&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;and SO&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;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&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, Mg&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;, Na&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;, K&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;and SO&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;and Cl&lt;/span&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;concentrations, and underestimates of H&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;concentrations.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/0004-6981(89)90063-2</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>A quality-assurance assessment for constituents reported by the National Atmospheric Deposition Program and the National Trends Network</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>