United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-89/018 Sept. 1989
&ER& Project Summary
Analysis of Acid Precipitation
Samples Collected by State
Agencies
Roger McCracken
This report presents the analytical
data from the 31 acid precipitation
collection sites in the State-Operated
Network. Samples are collected
weekly in plastic bag bucket liners
and shipped in 500 mL polyethylene
bottles to Global Geochemistry
Corporation (the central laboratory
for the network). The report contains
maps showing the location of each
site, plots of analytical data, tables of
all field and analytical data, plots
comparing field and laboratory pH
and conductivity, and information on
data quality.
Samples are analyzed for pH,
strong acid, conductivity, fluoride,
chloride, nitrite, phosphate, bromide,
nitrate, sulfate, ammonium, sodium,
potassium, calcium, and magnesium.
The central laboratory renders
technical assistance to the collection
sites on problems concerning pH and
conductivity. Each of the 11 parti-
cipating state agencies receive
analytical reports for the samples
analyzed the previous month. Analyte
concentration data are sent to the
Acid Deposition System (ADS) for
inclusion in the National Acid
Precipitation Data Base.
This Project Summary was devel-
oped by ERA'S Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
As the central laboratory for the State-
Operated Network, Global Geochemistry
Corporation (GGC) analyzes acid precip-
itation samples for pH, strong acid,
conductivity, fluoride, chloride, nitrite,
phosphate, bromide, nitrate, sulfate, am-
monium, sodium, potassium, calcium.
and magnesium.
The central laboratory provides the
collection sites with plastic bucket liners.
500 mL sample bottles, field data sheets.
pH and conductivity solutions, and other
supplies incidental to collecting and
shipping a collected rain sample. The
central laboratory also provides technical
assistance whenever it is requested by
the field sites. This assistance has con-
sisted mostly of advice on field pH and
conductivity measurement procedures
and equipment.
The final report contains maps showing
the location of each site, plots of
analytical data during the time period,
tables of all field and analytical data, a
comparison of analyte concentration at
deficient sites, precipitation weighted
data for each site, plots comparing field
and laboratory pH and conductivity, and
quality control tables and plots.
Each participating state agency and
sponsoring EPA Region receives an ana-
lytical report for the previous month's
analyses.
Data is summarized on magnetic tape
for inclusion in the yearly report of the
national acid rain data base, the Acid
Deposition System (ADS), funded by
EPA.
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Balance Accuracy
In the April 1987 survey of balance
accuracy, the respondents reported
differences from the expected value
ranging from -8.8 g to 1.4 g for the large
weight. Results from one site were
excluded from average performance
shown in Table 1 to avoid biasing the
average. The average difference from the
expected value was +0.01 grams. Using
the small weight, the reported difference
ranged from -0.39 g to +0.75 g. The
average difference was +0.04 grams.
A second balance accuracy survey was
conducted in March 1988. For 24
reporting sites, the differences from the
expected value ranged from -16.3 g to 1.9
g for the large weight. The average
difference from the expected value was -
0.9 g, however, one site was excluded
from the summary of average perform-
ance to avoid biasing the average.
The small weights were approximately
26 grams; the large weights 200 grams.
In most instances, an individual set of 2
weights was sent to each site with no
other field laboratory receiving the same
set. The central laboratory determined the
true mass of each weight.
pH and Conductivity
Semi-annual surveys of pH and
conductivity were performed. The results
of 3 survey periods are summarized in
Table 2. The results showed that incor-
rect pH measurements (errors greater
than 0.10 pH unit) may be occurring at
least 10 percent of the time.
For conductivity measurements, errors
in the range of 10 percent were evident at
20-25 percent of the sites in the April
1987 and March 1988 surveys.
The central laboratory assigned the
true values for pH and conductivity in the
surveys.
Discussion
There were 31 acid rain collection sites
in operation during most of 1987.The
State-Operated Network collects weekly
samples using a wet/dry bucket collector.
Samples are collected in a plastic bag
bucket liner, and an aliquot is sent to the
central laboratory unrefrigerated in a 500
mL polyethylene bottle.
The following analytes are measured:
pH, conductivity, strong acidity, chloride,
sulfate, phosphate, nitrate, ammonium,
sodium, potassium, calcium, and mag-
nesium. Plots are presented in the main
report showing the weekly concentration
of each analyte throughout the year. The
amount of precipitation is given for each
weekly collection period. Each site con-
ducts field measurements for pH and
conductivity. Representative plots are
presented in Table 3.
Once every two months the central
laboratory sends each collection site
replacement supplies, including 500 mL
of pH reference solution and 500 ml of
conductivity reference solution. Sites are
instructed to measure the reference
materials in the same way as a sample.
This procedure provides the sites with
on-going quality assurance self-checks of
the accuracy of their measurements.
The analytical methods used by the
central laboratory are shown in Table 4.
The occurrence of different concentra-
tion levels at each site are given in the
main report. The concentration at which
100%, 75%,50%, 25%, and 0% of
samples have concentrations greater!
than the given values are listed for each
site and for each analyte. This is
illustrated in Table 5 for pH.
Quality Control
To validate the accuracy of routine
analytical procedures, the central
laboratory included duplicate and spike
samples with all analyses. The duplicate
samples were randomly chosen acid
rain samples. Spike samples were
prepared from stock solutions and were
unknown to the analyst. Quality control
plots for all analytes are presented in
Appendix A of the main report.
Table 1. Summary of Survey of Balance Accuracy
Large weight (grams)
Small weight (grams)
Date
April 1987
March 1988
Average
difference*
0.01
-0.9
Range of
difference
-8.8 to 1.4
-76.3 to 7.9
Average
difference
0.04
0.00
Range of
difference
-0.39 to 0.75
-1.63 to 2.61
'Excluded ALMOB
Table 2. Summary of Survey of pH and Conductivity Accuracy
Date
April 1987
Sept. 1987
March 1988
PH
4.22
4.24
4.24
Survey
Std. dev.
0.14
0.04
0.06
averages
Conductivity
(pSlcm)
39.0
39.7
37.6
Expected values
Std. dev.
2.2
1.3
2.2
pH
4.26
4.26
4.28
Conductivity
37.8
37.8
37.4
Table 3. pH and Conductivity — Field vs. Laboratory
pH
Delum: pH Field - pH Lab vs Time
Conductivity
0.00 30.00 700.00 270.00 360.00
ID Number (Time) (X:0)1
<3 O Delum: Cond. Field - Cond. Lab vs Timt
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L Table 4. Analytical Methods
Analyte Analytical Method
ph
Conductivity
Acidity
CI', PO4-3 SCV2, NO3'
Naf, K*,
EPA Method 150.1
EPAMetho 120.1
Gran Titration
Ion Chromatography
EPA Method 350.1
EPA Methods 273.1,
258.1, 215.1, 242.1
Table 5. Cumulative Frequency of Occurrence: pH
% of Samples Greater Than Given Value
Site
ALTAL
ALMOB
DEGEO
DELUM
GADAW
GADUP
i GAHIW
GASUM
GAWAY
GABFG
KYGRA
KYMAM
LACAR
LACHS
LAROS
MDRGP
MDBBC
MSUNI
SCCAP
SCCON
SCDEL
SCLON
TNCEN
WVAPC
WVGRN
WVNEW
WVWAR
SDAPR
SDBGP
SDBPR
SDCUS
*Pt*
19
28
45
43
31
22
23
37
24
23
43
37
79
29
34
39
32
34
36
35
30
34
26
0
7
4
5
32
7
33
8
700%
4.77
3.70
3.27
3.48
4.00
3.97
3.99
3.74
4.03
3.74
3.77
3.84
4.75
4.22
3.97
3.55
3.57
4.00
4.02
3.64
3.87
3.87
3.84
0.00
4.69
4.02
3.93
4.47
5.83
4.46
4.98
75%
4.30
4.20
4,77
3.97
4.25
4.27
4,20
4.78
4.44
4.22 4
3.94
4.27
4.64
4.57
4.49
3.94
4.02
4.39
4.30
4.29
4.27
4.76
4.22
0.00
7.77
4.02
3.94
5.03
7.46
5.09
5.74
50%
4.54
4.38
4.38
4.78
4.38
4.50
4.38
4.34
^^.67
•H.4.7
Wt 4.17
4.32
5.05
4.69
4.74
4.03
4.34
4.55
4.53
4.45
4.47
4.32
4.34
0.00
2.35
4.03
4.07
5.49
2.92
5.46
5.40
25%
4.60
4.62
4.75
4.43
4.55
4.73
4.70
4.50
4.78
4.63
4.36
4.48
5.45
4.85
4.98
4.37
4.52
4.72
4.87
4.70
4.70
4.56
4.67
0.00
3.52
4.22
4.78
5.65
4.37
5.72
5.69
0%
4.90
5.67
5.96
4.97
5.20
5.07
5.02
4.89
5.24
5.00
5.57
6.37
6.07
5.27
5.57
4.72
5.45
6.50
5.76
4.97
6.85
5.00
4.79
0.00
4.69
4.43
4.44
6.44
5.83
6.50
6.33
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Roger McCracken is with Global Geochemistry Corporation, Canoga Park, CA
91303.
Berne I. Bennett is the EPA Project Officer (see below).
The complete report, entitled "Analysis of Acid Precipitation Samples Collected by
State Agencies," (Order No. PB 89-155 279/AS; Cost: $42.95, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
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