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 7. Regional comparison of observed 1995 annual and bi-monthly ionic concentrations at NADP/NTN sites
with values predicted by the seasonalized trend model using data from 1983 through 1994.
Frequency of observed 1995 concentrations that were less than predicted
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Annual January- March- May- July- September- November-
Number of Mean February April June August October December
Valid 1995 --------- --------- --------- --------- --------- --------- ---------
Region Estimates n % n % n % n % n % n % n %
------------------------------------------------------------------------------------------------------------
--------------------------------------------- Hydrogen Ion -------------------------------------
East 62 55 88.7 45 72.6 28 45.2 46 74.2 41 66.1 53 85.5 44 71.0
NE 47 43 91.5 36 76.6 24 51.1 35 74.5 28 59.6 42 89.4 37 78.7
SE 15 12 80.0 9 60.0 4 26.7 11 73.3 13 86.7 11 73.3 7 46.7
West 47 15 31.9 29 61.7 24 51.1 22 46.8 18 38.3 19 40.4 28 59.6
Total 109 70 64.2 74 67.9 52 47.7 68 62.4 59 54.1 72 66.1 72 66.1
------------------------------------------------ Sulfate ---------------------------------------
East 62 49 79.0 40 64.5 30 48.4 45 72.6 41 66.1 47 75.8 43 69.4
NE 47 39 83.0 32 68.1 24 51.1 34 72.3 30 63.8 39 83.0 36 76.6
SE 15 10 66.7 8 53.3 6 40.0 11 73.3 11 73.3 8 53.3 7 46.7
West 47 17 36.2 28 59.6 30 63.8 22 46.8 20 42.6 15 31.9 25 53.2
Total 109 66 60.6 68 62.4 60 55.0 67 61.5 61 56.0 62 56.9 68 62.4
------------------------------------------------ Nitrate ---------------------------------------
East 62 24 38.7 36 58.1 20 32.3 33 53.2 22 35.5 43 69.4 17 27.4
NE 47 20 42.6 30 63.8 16 34.0 24 51.1 15 31.9 35 74.5 15 31.9
SE 15 4 26.7 6 40.0 4 26.7 9 60.0 7 46.7 8 53.3 2 13.3
West 47 20 42.6 25 53.2 27 57.4 29 61.7 24 51.1 17 36.2 26 55.3
Total 109 44 40.4 61 56.0 47 43.1 62 56.9 46 42.2 60 55.0 43 39.4
------------------------------------------------ Chloride --------------------------------------
East 62 14 22.6 22 35.5 27 43.5 27 43.5 24 38.7 22 35.5 25 40.3
NE 47 10 21.3 19 40.4 20 42.6 21 44.7 21 44.7 17 36.2 17 36.2
SE 15 4 26.7 3 20.0 7 46.7 6 40.0 3 20.0 5 33.3 8 53.3
West 47 16 34.0 26 55.3 22 46.8 22 46.8 13 27.7 15 31.9 27 57.4
Total 109 30 27.5 48 44.0 49 45.0 49 45.0 37 33.9 37 33.9 52 47.7
------------------------------------------------ Ammonium --------------------------------------
East 62 17 27.4 20 32.3 20 32.3 29 46.8 21 33.9 33 53.2 18 29.0
NE 47 13 27.7 16 34.0 16 34.0 24 51.1 19 40.4 25 53.2 16 34.0
SE 15 4 26.7 4 26.7 4 26.7 5 33.3 2 13.3 8 53.3 2 13.3
West 47 17 36.2 26 55.3 30 63.8 26 55.3 21 44.7 15 31.9 22 46.8
Total 109 34 31.2 46 42.2 50 45.9 55 50.5 42 38.5 48 44.0 40 36.7
------------------------------------------------ Calcium ---------------------------------------
East 62 4 6.5 25 40.3 15 24.2 20 32.3 20 32.3 22 35.5 7 11.3
NE 47 2 4.3 24 51.1 10 21.3 14 29.8 12 25.5 18 38.3 6 12.8
SE 15 2 13.3 1 6.7 5 33.3 6 40.0 8 53.3 4 26.7 1 6.7
West 47 11 23.4 23 48.9 20 42.6 22 46.8 11 23.4 13 27.7 18 38.3
Total 109 15 13.8 48 44.0 35 32.1 42 38.5 31 28.4 35 32.1 25 22.9
----------------------------------------------- Magnesium --------------------------------------
East 62 3 4.8 21 33.9 13 21.0 16 25.8 9 14.5 10 16.1 15 24.2
NE 47 1 2.1 19 40.4 10 21.3 10 21.3 6 12.8 8 17.0 8 17.0
SE 15 2 13.3 2 13.3 3 20.0 6 40.0 3 20.0 2 13.3 7 46.7
West 47 7 14.9 24 51.1 11 23.4 14 29.8 9 19.1 12 25.5 18 38.3
Total 109 10 9.2 45 41.3 24 22.0 30 27.5 18 16.5 22 20.2 33 30.3
----------------------------------------------- Potassium --------------------------------------
East 62 6 9.7 16 25.8 15 24.2 16 25.8 23 37.1 20 32.3 19 30.6
NE 47 4 8.5 14 29.8 11 23.4 9 19.1 18 38.3 13 27.7 10 21.3
SE 15 2 13.3 2 13.3 4 26.7 7 46.7 5 33.3 7 46.7 9 60.0
West 47 11 23.4 21 44.7 20 42.6 25 53.2 13 27.7 18 38.3 18 38.3
Total 109 17 15.6 37 33.9 35 32.1 41 37.6 36 33.0 38 34.9 37 33.9
------------------------------------------------ Sodium ----------------------------------------
East 62 5 8.1 21 33.9 20 32.3 12 19.4 9 14.5 6 9.7 16 25.8
NE 47 1 2.1 17 36.2 13 27.7 6 12.8 7 14.9 3 6.4 9 19.1
SE 15 4 26.7 4 26.7 7 46.7 6 40.0 2 13.3 3 20.0 7 46.7
West 47 5 10.6 28 59.6 18 38.3 12 25.5 3 6.4 10 21.3 18 38.3
Total 109 10 9.2 49 45.0 38 34.9 24 22.0 12 11.0 16 14.7 34 31.2
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