The U.S. Geological Survey (USGS) Precipitation Chemistry Quality Assurance
Project operates the external quality assurance (QA) programs for the National
Atmospheric Deposition Program (NADP)
. The NADP has monitored the effects of
wet deposition across the United States since 1978 and provides scientific investigators
with a long-term, high-quality database of atmospheric-deposition information.
The NADP consists of three monitoring networks that are used to collect precipitation
depth data and atmospheric deposition samples for chemical analysis: (1) National
Trends Network (NTN), (2) Atmospheric Integrated Research Monitoring Network
(AIRMoN), and (3) Mercury Deposition Network (MDN).
The USGS external QA programs are designed to: (1) evaluate potential contamination due to handling,
processing, and shipping of samples, along with contamination introduced from field exposure of the samples;
(2) estimate the variability and bias of analytical results determined by separate laboratories routinely
measuring wet deposition; (3) facilitate integration of data from various monitoring networks; and (4) estimate
the overall variability of the NADP data, from the point of sample collection through laboratory data quality
Precipitation samples are collected weekly for analysis at approximately 300
NADP sites across the country. The information gained from monitoring the chemistry
of our Nation's precipitation is essential for evaluating the effectiveness
of emission control efforts and in determining trends in precipitation quality.
The USGS provides about one-third of the funding
for the operation of NADP sites. It is USGS policy to quality assure the data obtained from its
monitoring programs and studies. Therefore, the USGS provides the external quality assurance project
for the NADP. The information gained from monitoring the chemistry of the Nation's precipitaton is
essential to integrated water quality assessments at the watershed, regional and national levels. Without
quality assurance efforts of the USGS, the error component of NADP data would be largely unknown and the
usefulness of the network's data in environmental studies would be diminished.