Encyclopedia of Environmental Science and Engineering, Volume I and II

ACID RAIN 9

(c) Precipitation samples are relatively clean or pure as

compared to treated well water used for drinking.

SPATIAL PATTERNS. The spatial distribution of five

of the chemical parameters measured in the NADP/NTN

weekly precipitation chemistry samples are shown in

Figures 2–6. The “” symbol indicates the location of the

180 sampling sites included in the analysis. A relatively

long time period (1990–1993) was chosen for analysis in

order to have sufficient data to produce stable patterns,

but not so long that emissions of the major sources of the

chemical parameters would have changed substantially.

Samples for weeks with total precipitation less than two

hundredths of an inch of equivalent liquid precipitation

were not included. Every sample was required to pass rigor-

ous quality assurance standards which included checks to

assure that the proper sampling protocol was followed and

that visible matter in the samples was not excessive and did

not produce abnormally high concentrations of the chemi-

cal species measured. The nine sites at elevations greater

than 3,000 meters were not included due to concerns about

their representativeness. Completeness of data for each of

the sites was judged in two ways. First, sites that started

after January 1, 1990, or ceased operating before December

31, 1993, were excluded from the analysis if they operated

TABLE 2

Median Ion Concentrations for Drinking Water and for Wet Deposition at Four NADP/NTN Sites in

Four States for 1984

New

Hampshirea Ohiob Nebraskac Floridad

Drinking

Watere

Number of Samples 35 37 41 46 5

Ions (meq/L)

SO 42  (Sulfate) 37 69 43 21 650

NO 3  (Nitrate) 23 32 28 10 3

Cl (Chloride) 4 7 3 27 234

HCO 3  (Bicarbonate) 0.1f 0.1f^3 f 0.7f^2044 f

Sum (rounded off ) 64 108 77 59 2931

NH 4  (Ammonium) 7163 63 2 8

Ca^2  (Calcium) 4 9 22 9 624

Mg^2  (Magnesium) 2 4 5 6 905

K (Potassium) 0.4 0.6^1161

Na (Sodium) 4 3 4 24 1444

H (Hydrogen)g 41 71 2 7 
.1

Sum (rounded off ) 58 104 70 50 3062

Median pH 4.39 4.15 5.80 5.14 About 8.6

Weighted pHh 4.41 4.16 5.07 5.05 —

Calculated pH 4.33 4.12 5.17 4.93 —

a A site in central New Hampshire.

b A site in southeastern Ohio.

c A site in east-central Nebraska.

d A site in the southern tip of Florida.

e Levels in treated municipal well water (tap water) for a city of 100,000 in Illinois.

f Calculated with equation: HCO 3   5.13 divided by H^ ^ for Pco 2  335  10 ^6 atm.

g Calculated from median pH.

h Sample volume weighted hydrogen ion concentration, expressed as pH. Some western sites have

differences in weighted and median pH values of as much as 1 unit.

FIGURE 2 Median concentration (mg/L) of sulfate in precipita-

tion for 180 NADP/NTN sites for the period 1990–1993.

1.00

3.50

2.00

2.50

0.50

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