Investigation of differences between field and laboratory pH measurements of national atmospheric deposition program/national trends network precipitation samples

Water, Air, & Soil Pollution
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Abstract

A study was undertaken to investigate differences between laboratory and field pH measurements for precipitation samples collected from 135 weekly precipitation-monitoring sites in the National Trends Network from 12/30/1986 to 12/28/1999. Differences in pH between field and laboratory measurements occurred for 96% of samples collected during this time period. Differences between the two measurements were evaluated for precipitation samples collected before and after January 1994, when modifications to sample-handling protocol and elimination of the contaminating bucket o-ring used in sample shipment occurred. Median hydrogen-ion and pH differences between field and laboratory measurements declined from 3.9 ??eq L-1 or 0.10 pH units before the 1994 protocol change to 1.4 ??eq L-1 or 0.04 pH units after the 1994 protocol change. Hydrogen-ion differences between field and laboratory measurements had a high correlation with the sample pH determined in the field. The largest pH differences between the two measurements occurred for high-pH samples (>5.6), typical of precipitation collected in Western United States; however low- pH samples (<5.0) displayed the highest variability in hydrogen-ion differences between field and laboratory analyses. Properly screened field pH measurements are a useful alternative to laboratory pH values for trend analysis, particularly before 1994 when laboratory pH values were influenced by sample-collection equipment.
Publication type Article
Publication Subtype Journal Article
Title Investigation of differences between field and laboratory pH measurements of national atmospheric deposition program/national trends network precipitation samples
Series title Water, Air, & Soil Pollution
DOI 10.1023/B:WATE.0000022971.59349.fc
Volume 154
Issue 1-4
Year Published 2004
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Water, Air, and Soil Pollution
First page 249
Last page 270
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