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
Table 2. Mean µeq/L and percent changes in ionic concen-
trations of precipitation collected at NADP/NTN
sites from 1983 through 1994.
Mean change in conc.
Mean change in conc. for sites with
for all sites significant* trends
____________________ ____________________
Region (µeq/L) Percent (µeq/L) Percent
------------------------------------------------------------
----------------- Hydrogen Ion -----------------
East -3.69 -8.2 -8.56 -17.8
NE -4.61 -10.1 -9.44 -20.3
SE -1.15 -3.0 8.06 29.0
West -1.71 -18.3 -3.93 -42.1
Total -2.68 -13.4 -6.25 -29.9
------------------- Sulfate --------------------
East -5.94 -13.8 -9.86 -22.8
NE -6.57 -13.9 -10.43 -22.2
SE -4.22 -13.4 -7.78 -24.7
West -3.71 -18.9 -5.73 -28.7
Total -4.80 -16.4 -7.69 -25.9
------------------- Nitrate --------------------
East -0.29 1.0 1.74 15.5
NE -0.51 -0.4 0.61 6.8
SE 0.34 5.1 4.02 32.8
West 1.00 17.6 3.91 64.4
Total 0.37 9.5 3.34 51.6
------------------- Chloride -------------------
East -0.89 -16.3 -1.30 -27.3
NE -0.83 -17.3 -1.25 -27.3
SE -1.06 -13.5 -1.87 -26.9
West -1.47 -24.3 -1.61 -35.6
Total -1.18 -20.4 -1.49 -32.3
------------------- Ammonium -------------------
East 1.14 13.6 3.46 49.8
NE 1.14 11.4 3.71 37.4
SE 1.15 19.8 3.16 65.2
West 3.47 42.3 6.40 86.6
Total 2.33 28.2 5.65 77.1
-------------------- Calcium -------------------
East -1.85 -28.5 -2.33 -36.0
NE -1.88 -26.0 -2.36 -32.8
SE -1.77 -35.4 -2.27 -45.2
West -2.57 -27.3 -3.46 -42.2
Total -2.22 -27.9 -2.80 -38.6
------------------ Magnesium -------------------
East -0.93 -37.5 -1.03 -42.7
NE -0.97 -39.5 -1.04 -43.1
SE -0.81 -31.9 -1.00 -41.3
West -1.27 -41.8 -1.47 -48.8
Total -1.10 -39.7 -1.24 -45.6
------------------ Potassium -------------------
East -0.13 -21.3 -0.23 -37.2
NE -0.14 -23.8 -0.24 -41.3
SE -0.11 -14.5 -0.18 -19.3
West -0.22 -25.5 -0.36 -42.1
Total -0.18 -23.5 -0.29 -39.5
-------------------- Sodium --------------------
East -0.53 -14.3 -1.01 -29.4
NE -0.52 -16.2 -0.90 -30.4
SE -0.57 -9.2 -1.52 -25.2
West -1.14 -20.7 -1.99 -43.7
Total -0.84 -17.6 -1.52 -36.8
*p<0.05
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Last Update: 1536 08JUL96 kjl