U.S. Geological Survey Open-File Report 09-0346
Trends in Precipitation Chemistry in the United States,
1983-1994: An Analysis of the Effects in 1995 of Phase I of the Clean Air Act Amendments of 1990, Title IV
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Table A.1.
Algorithms for adjusting pre-1994 NADP/NTN data
for the effects of contamination from the lid o-ring. The “cor”
and “unc” subscripts designate the concentrations that are
corrected or uncorrected for the o-ring. Volume (Vol) is in mL
and pH is in pH units. Volume restriction categories for the
algorithms with volume and pH factors are listed. These
corrections effectively limit the size of the corrections at very low
and very high pH values.
Volume-Only Factors:
Cacor = Caunc - (3.70/Vol) (1 - exp-0.00214Vol)
Mgcor = Caunc - (2.21/Vol (1 - exp -0.00252Vol)
NH4cor = NH4unc - (8.46/Vol (1 - exp-0.00287Vol)
Clcor = Clunc - (5.04/Vol) (1 - exp-0.00269Vol)
Volume and pH Factors:
A.
For pH > (5.13 + (2000/Vol)], use the minimum of [5.13 +
(2000/Vol)] or 6.86
For pH < (5.13 + (2000/Vol)], use the maximum of [5.13 +
(2000/Vol)] or 3.80
Kcor = Kunc - [(61.25 - 23.19pH = 2.20pH2 )/Vol][1 - exp-0.00552Vol]
NO3cor = NO3unc - [(146.29 - 50.47ph + 4.64pH2)/Vol][1- exp-0.00593Vol]
B.
For pH > (5.13 + (2000/Vol)], use the minimum of [5.13 +
(2000/Vol)] or 6.72
For pH < (5.13 + (2000/Vol)], use the maximum of [5.13 +
(2000/Vol)] or 3.80
Nacor = Naunc - [(163.66 - 64.07pH + 6.46pH2)/Vol][1 - exp-0.00246Vol]
C.
For pH > (5.13 + (2000/Vol), use the minimum of (5.13 +
(2000/Vol) or 6.67
For pH < (5.13 + (2000/Vol), use the maximum of (5.13 +
(2000/Vol) or 3.80
SO4cor = SO4unc - [(177.73 - 53.44pH + 4.62pH2)/Vol][1 - exp-0.00230Vol]
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Last Update: 1536 08JUL96 kjl