G E O C H E M I C A L I N V E S T I G A T I O N S O N A T M O S P H E R I C

P R E C I P I T A T I O N I N A M E D I U M - S I Z E D C I T Y

( G O T T I N G E N , F . R . G . )

HANS R U P P E R T

Geochemisehes Institut der Universitiit Gdttingen, D-34 GOttingen, Goldsehmidtstrasse 1, F.R.G.

(Received 13 February, 1975)

Abstract. The concentration of 27 elements was investigated in 10 samples of precipitation from G6ttingen, collected during May and September 1972. G6ttingen is a non-industrial town of 130000 inhabitants, situated in a rural area, and essentially all the dissolved and undissolved material in rainwater is locally derived. Elemental concentrations in freshwater and shale are used for compari- son 'with the dissolved elements in precipitation and the undissolved residue. The two phases have been separated after evaporation (concentration factors: 15 to 25-times). Phosphorous, Zn, Mn, and Pb are enriched in rainwater, while Si, Mg, Na, Ca, CI, Fe, Hg, K, Li, and AI are depleted relative to average freshwater. Sulfate, Cd, and Cu have similar concentrations in rain and freshwater. The factors of accumulation between elements in residue and average shale are calculated after normali- zation to the Al-value. They are: >/100 for Ag, Hg, Pb; between 10 and 20 for Zn, Cd, P, Cu, Mo; > 2 for Cr, Bi, Ni, Ba, Ti, V; between 0.9 and 2.0 for Rb, K, Na, Li, Mg, Mn, Fe, Si, Ca; and 0.5 for TI.

The trace element accumulation is due to different anthropogenic sources: combustion of liquid petroleum fuels contributes to Pb, V, Ni, Mo, Hg, and sulfate, combustion of coal to Ba, sulfate, and chloride, and to the. readily volatile elements such as Hg, Cd, T1, Bi, and Ag, combustion of refuse to Ag, Bi, Pb, Cd, Hg, Zn, Cr, Cu, Ba, and Mo in highly variable amounts. Fertilizers and road salts change the chemistry of soils and indirectly supply P, alkali and alkaline-earth metals to the fly dust. Modest industrial activity is responsible for high Cu and Cr concentrations.

Despite the appreciable accumulation of some toxic elements, the precipitation in G6ttingen is relatively pure compared to other areas. Favorable geologic conditions around G6ttingen decrease the negative influences of potentially harmful airborne elements. The high carbonate content in the dust neutralizes the anthropogenic acids in the rainwater. Furthermore, the toxic trace elements are diluted, especially in the center of G6ttingen, by a large amount of airborne dust.

Introduction

This s tudy using env i ronmenta l analysis was in i t ia ted to de te rmine levels and sources

o f a tmospher ic trace elements in a med ium size non- indus t r ia l ized city. Ten samples

o f p rec ip i t a t ion were collected f rom M a y 10 to June 4, 1972, and f rom September 1

to Oc tober 1, 1972, in G6t t ingen. The town, s i tuated in a rura l area, has 130000 in-

habi tants . Wind direct ion and geomorpho log ica l barr iers keep the supply o f e lements

f rom the indust r ia l areas o f Kassel (40 k m southwest o f G6t t ingen) and o f Salzgit ter

(65 k m nor theas t ) at a min imum. This means G6t t ingen is main ly receiving local ly

derived mater ia l in its precipi ta t ion.

1. Methods of Sampling and Analysis 1.1. SAMPLING

The five sites chosen for sampl ing were the Geophys ica l Inst i tute, the 'F r iedensk i rche ' ,

the G6t t ingen city hall, the as t ronomica l observatory , and the weather observatory .

Water, Air, and Soil Pollution 4 (1975) 447-460. All Rights Reserved Copyright © 1975 by D. Reidel Publishing Company, Dordrecht-Holland

448 HANS RUPPERT

For sample collecting the following equipment was used according to the VDI-rule 2119 (May, 1971). Four polyethylene funnels, each 25.2 cm in diameter, were com- bined to a unit with an effective surface of 2000 cm z. As protection against possible contamination of the samples by bird droppings, the funnels were crowned with a sharply serrated plastic material. The collectors were mounted at a height of 10 to 20 m above ground in order to reduce local influences. The polyethylene bottles were wrapped in black water-resistent paper to prevent growths of algae. After sampling, the bottles contained the total deposition, both the wet portion plus a dry portion, which was washed from the funnel into the container by subsequent rain.

1.2. PREPARATION FOR ANALYSIS

Material greater than 1 mm (flies and fibers) was separated from the samples by screening. The samples were evaporated 15 to 25 times in a dark clean room at about 35 °C, and then filtered with Sartorius 0.1 pm diameter membrane filters, which were weighed to determine the insoluble residue. The filtrate was brought to a volume of 500 ml and frozen until analysis. Part of the residue was heated to 550°C to measure loss on ignition and then completely digested by hydrofluoric and perchloric acids.

1.3. ANALYSIS

By using Debye-Scherrer X-ray diffraction together with a Perkin-Elmer grating IR spectrophotometer 457 it was possible to detect quartz, illite-muscovite, plagioclases, and potassium feldspars along with organic phases. Iron oxyhydroxides could not be identified because of poor cristallinity; the X-ray diagrams show diffuse reflections in the range of 2.45-2.70 A, sometimes with peaks at 2.52 and 2.70 A, which suggest the occurrence of hematite.

Microscopic studies showed maximum grain sizes of minerals to be 90/~rn in dia- meter, those were leaf-shaped, light brown grains of mica and yellow to redbrown flakes of oxidized iron. Medium-sized minerals of quartz and feldspars were 5 to 10/~m in diameter, with a maximum of 20 #m. The mineral grains occur between cords of fibers with a length of 100 to 1000 pro, being well rounded and often incrusted with yellow brown ferri-oxihydroxides.

Atomic absorption spectroscopic analysis with and without flame was performed with the Perkin-Elmer double beam spectrophotometer 303. All standard solutions were a mixture of the main elements found in the samples. The analysis of the ele- ments A1, Ca, Cu, Fe, K, Mg, Mn, Na, and Zn was carried out by flame AAS using the methods of Brown et al. (1970), Herrmann (1971), and Luecke (1971). The working conditions for the determination of Cd, Cu, Fe, Pb, Hg, Cd, Bi, and T1 by flameless AAS, using the heated graphite tube atomizer HGA 70, are described by Heinrichs and Lange (1973) and Heinrichs (1975a, b). Li and Rb were measured with similar conditions: sample volume 20 or 50/d, thermal decomposition at 750°C and atomiza- tion at 2400°C for 40 s. Mercury, Cd, Bi, and T1 were determined in the residue after preenrichment by volatilization.

Spectrophotometric analysis, made with the Zeiss prism spectrophotometer PMQ II,

GEOCHEMICAL INVESTIGATIONS ON ATMOSPHERIC PRECIPITATION 449

were used for P, Si, and Ti (Herrmann, 1971) and sulfate (Zimmermann, 1967). A combination electrode was used for pH determination and subsequent acidity

titration immediately after sampling. The CO2 content is calculated according to Brown et al. (1970). Chloride was determined mercurometrically with potentiometric indication of the equivalence point, using a Metrohm potentiograph E 436. The water samples were titrated automatically with 0.001 N Hg(NO3)2 solution using an amal- gamated Ag indicator electrode and a graphitic reference electrode. Recording and counter voltage were both 100 inV. Addition of ethanol to the samples improved the character of the titration curve. No other ions in the solution interfered with the chloride determination. Both bromide and iodide were at the limit of detection.

D.C. arc optical emission spectrographic analysis was performed with the 3.4 m- Ebert-spectrograph of Jarrell-Ash (15 000 lines in.-1 grating). After a short thermal decomposition of the residue at 500°C the sample was arced. The element In (3039) served as internal standard for Ag (3281) and Pb (2833). Iron (3184) was used as a variable internal standard for Ba (3071), Cr (3005), Mo (3170), Ni (3051), and V (3185). The relative standard deviation for all determinations is about 10%.

The Si concentration is calculated as the difference between 100 and the sum of the oxides of the determined elements.

2. Results and Discussion

Table I shows the average amount of rain, pH, CO 2 content, and total amounts and concentrations of the pollutants in the rainwater. Averages and ranges of the total amount of elements in rainwater and inorganic residue are given in Table II. The chemical compositions of rainwater and residue are listed in Tables III, IV, and V together with data for comparison, which could reveal the origin of the elements in the atmosphere. All ppm are part per million by weight.

A_s the samples were concentrated by evaporation 15 to 25-times before analysis, the', less soluble elements (Si, Hg, Fe, A1) are precipitated corresponding to their solubility, and are enriched in the residue. On the other hand, rainwater partly leaches the soluble elements from the solids during the time of sampling and evaporation.

2.1. COMPARISON OF CONCENTRATION OF DISSOLVED ELEMENTS IN THE RAINWATER SAMPLES WITH FRESHWATER (Table III)

It is evident that the elements P, Zn, Mn, and Pb are enriched in our rainwater samples, and that Mg, Na, chloride, Ca, K, and Li are diluted relative to freshwater; sulfate, Cd, and Cu are intermediate. The higher concentration of Mg and Ca in the local river and lake water is apparently caused by the carbonate rich soils and rocks of the area (see Section 2.2), the higher K, Na, and Mg concentration is caused by fertilizers, which are added to the soils. Local influences dominate over aerosols which originated from the surface of the ocean. This can be shown by the large fluctuations of C1 and Na and furthermore by the ratio of these two elements. Junge and Werby (1958) observed concentrations of 0.2 to 0.3 ppm for both elements (ratio 0.75 to 1) several

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GEOCHEMICAL INVESTIGATIONS ON ATMOSPHERIC PRECIPITATION 451

TABLE II

Mean and range of the total concentrations of elements from rain and residue and dissolved portion of an clement in percent of its total concentration

Rainwater Residue Sum Dissolved

mg mg mg

( m T X ~ d a ~ ) (m2 × 30 dayys) (m~ × 30 d a y s ) ( ~ )

Mean Range Mean Range of means A - - x 100

A B A + B A + B

Ag × 10 -3 A1 5.0 1.9-10.8 Ba Bi x 10 -a Ca 134 .88-258 Cd × 10 .3 29 5-55 C]I 46 25-76 Cr Cu 0.43 0.05-2.05 Fe 2.3 0.4-6.3 Hg × 10 -a 2.0 1.4-2.7 K 30 19-54 Li × 10 .3 24 8-.45 Mg 16 9-26 Mn 1.4 0.7-2.3 Mo × 10 -3 Na 28 19-43 Ni P 12.8 5.5-22 Pb 0.33 0.04-0.70 Rb SO2-4 453 330-580 Si 4.3 1.4-10.1 Ti T1 X 10 -3 V Zn 2.7 1.3.4.2

13 5-42 77 30-168 82 6

1.5 0.3-3.9 1.4 0 . 4 - 1 . 9

30 9-84 164 82 3.4 0.5-7.3 32 91

0.76 0.16-1.72 0.44 0.26-0.96 0.87 49

77 30-171 79 3 82 42-150 84 2 25 10-54 55 55 52 30-100 76 32 21 5-58 37 43 1.0 0.4-2.2 2.4 57 24 8-41 16 4-40 44 64

0.20 0.08-0.48 6.3 5.0-8.6 19 67

1.58 0.63-2.49 1.91 17 0.11 0.04-0.23

383 120-930 387 1 11 4-30

0.43 0.26-0.65 0.26 0.11-0.57

1.2 0 . 6 - 1 . 8 3.9 69

hundred kilometers from the East coast of the United States. Rainwater in G6ttingen contains 1 ppm C1 and 0.6 ppm Na (ratio 1.7). Influence of marine aerosols on other elements is not to be expected, and is not observed.

2.2. COMPARISON OF ELEMENTAL CONCENTRATIONS IN SAMPLE RESIDUE WITH

AVERAGE SHALE AND CARBONATES (Table 1V a n d V)

Average shale composition gives background values for the composition of the resi- dues. Factors of accumulation for the elements are calculated according to (Cel . . . . t/ CAl)r~sidue :(Ce~ . . . . t/CA1)shale with C representing the concentration. Local differences in the composition of shale and geochemical anomalies are neglected. Nearly all elements (except T1 and Rb) are accumulated in the residue relative to average shale (factors of enrichment in brackets): Ag, HA, Pb (~> 100); Zn, Cd, P, Cu, Mo (20 to 10);

452 HANS RUPPERT

TABLE III

Elemental concentrations in rainwater, average freshwater, and local waters from the Kiessee pond and Leine River near GSttingen

Concentrations (ppb) Factors Rainwater Fresh- Leine, of (this work) water 1 Kiessee ~ accumulation

Mean Range Mean Mean A B C B/A C/A

A1 89 48-174 300 55 3.4 0.62 Ca 2620 1470-3670 17500 120000 6.7 46 Cd 0.50 0.12-0.95 0.61 ~ 0.3 1.2 0.60 C1 870 300-1870 6700 7.7 Cu 6.8 1.2-13.9 7 3.2 1.0 0.47 Fe 43 5.1-45 230 28 5.4 0.65 Hg 0.039 0.023~).075 0.15 a 0.21 3.8 5.4 K 600 298-1270 2200 6500 3.7 11 Li 0.44 0.18~9.92 1.6 3.6 Mg 282 169-476 3800 22500 13 80 Mn 25 18-44 9 5.9 0.36 0.24 Na 540 234-1000 6000 14000 11 26 P 230 130-500 20 ? 0.09 ? Pb 5.4 0.50-15.1 2.0 a 0.6 0.37 0.11 SO2-4 8800 4500-12800 11600 1.3 SiO2 146 75-320 36400 250 Zn 48 12-77 10 5.5 0.21 0.11

1 Wedepohl (1968); ~ Heinrichs (1974a, b): additional data are typical of German river and lake water.

Heinrichs (1975a, b): The samples from Kiessee and Leine were taken in October 1972.

Cr, Bi, Ni , Ba, Ti, V ( > 2 ) ; Fe, Si, Mn, M g ( > 1). Li th ium, Na, K, and R b are a b o u t

equal to their concent ra t ion in shale (factor 1).

The ma in source o f dust is the intensively cul t ivated rura l area a r o u n d G6t t ingen,

which is composed of grey-brown podsol ic soils developed f rom calcerous loess im-

media te ly in the sampl ing area, and soils overlying layers of Musche lka lk (argi l laceous

l imestones, do lomi t ic marl , and calcerous shales) and Keuper (sandstones, quartzi te ,

mar l with dolomi t ic interlayers) to the west and east. Limestone d id no t change the

compos i t ion of the residue much after being dissolved in ra inwater , because the

remain ing siliceous pa r t according to W e d e p o h l (1970) mainly cor responds to the

compos i t ion o f shale except 3 3 ~ more Mg, 14~ more Mn, 9 ~ more Fe, and 6~o

more A1 in the residue plus solute (Table V). The remain ing amounts of elements

are less than 5~ .

2.3. ADDITIONAL SOURCES OF ELEMENTS (Table IV and V)

Enr ichment factors higher than 1 relative to shale indicate addi t iona l supplies of

accumula ted elements:

G E O C H E M I C A L I N V E S T I G A T I O N S O N A T M O S P H E R I C P R E C I P I T A T I O N 453

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TABLE V

Composition of averages carbonates and abundant organic material (dry insects and land plants) from literature; computed contributions from these sources to the ele-

ments from the investigated samples in percent of residue q- solute (Table II)

Concentrations (ppm) Fraction of elements ( ~ ) in residue ÷ solute* from:

Average Dry Dry Average Dry Dry carbonates1 insects ~ plants ~ carbonates insects plants

Ag 0.0 × 0.07 0.06 <0 .0 × <0.65 <0.56 A1 10300 100 500 5.9 0.15 0.76 Ba 120 14 <3.7 <1.1 Bi 0.070 ~ 0.06 < 2.4 Ca 315000 500 18000 91 0.38 14 Cd 0.15 a 0.6 2.5 0.02 C1 150 1200 2000 <0.16 <2.9 <4.8 Cr 11 0.23 < 0 68 <0.04 Cu 4 50 14 0.22 7.2 2.0 Fe 14600 200 140 8.7 0.32 0.22 Hg 0.033 a 0.02 0.02 0.03 K 4700 11000 14000 4.0 25 31 Li 7.5 7 0.1 4.7 12 0.17 Mg 26000 750 3200 33 2.5 11 Mn 700 10 630 14 0.53 33 Mo 0.4 0.6 0.9 <0.80 < 3.2 <4.7 Na 1300 3000 1200 1.4 8.4 3.4 Ni 15 9 3 <3.6 <5.7 <1.9 P 300 17000 2300 0.74 110 15 Pb 5 a 7 2.7 0.15 0.46 0.18 Rb 11 20 <4.8 <23 S 1200 4400 3400 <0.38 <3.6 <2.8 Si 35000 6000 500 4.3 1.9 0.16 Ti 400 160 1 <1.7 <1.8 <0.01 T1 0.11 ~ <12 V 20 0.15 1.6 <3.6 <0.07 <0.78 Zn 20 400 100 0.24 13 3.2

* 149 mg Ca × m -2 × (30 days) -1 and 1250 mg Corg × m -~ × (30 days) -1 are the basis for calculation. Data from: 1 Wedepohl (1970); a Heinrichs (1975a, b) (mean of composite limestones from the Devonian, Jurassic, and Cretaceous of Europe). 2 Bowen (1966).

2.3.1. Combustion of Oil ( T a b l e IV)

P e t r o l e u m fuels a n d a u t o m o b i l e ga so l i ne s re lease V, Ni , M o , Hg , a n d su l fa t e in

v a r i a b l e b u t a p p r e c i a b l e a m o u n t s d u r i n g b u r n i n g . G a s o l i n e is a l so a n i m p o r t a n t s o u r c e

o f P b ( a n t i k n o c k agen t ) . C o m b u s t i o n o f oil is n o t e x p e c t e d to c o n t r i b u t e s ign i f i can t ly

t o o t h e r e l e m e n t s , b e c a u s e t h e i r c o n c e n t r a t i o n in fuels is t o o low.

GEOCHEMICAL INVESTIGATIONS ON ATMOSPHERIC PRECIPITATION 455

2.3.2. Combustion of Coal (Table IV)

Comparing the composition of the residue with the analysis of coal and related fly ash, only the elements T1, Ba, Mo, and P are enriched in the ashes. The data of Bertine and Goldberg (1971) show high concentrations of the elements Bi, Hg, Rb, and Ni in coal residues. Coals of the European Carboniferous contain up to 27000 ppm Ba (Puchelt, 1972). The influence of the fly ash on the main components can be estimated by the analysis of coal ash from the Ruhr area (W. Germany) : Si-194000, A1-164000, Fe- 129 000, Mn-5400, Mg- 10 300, Na + K (soluble)- about 38 000, P-2200, S- 1600 ppm (Goldschmidt and Peters, 1933). Large amounts of fly ash in the samples are not anticipated, since higher A1 concentrations should have been found. The samples show, however, the concentration of A1 is below that of shale. Rb should be more concentrated also.

Burning of coal probably contributes a major proportion to volatiles such as Bi, Cd, Hg, Tl, and Ag in the atmosphere, because they reach the atmospheric environ- ment as a vapor. This is obvious from the ratio: (elemental concentration in fly ash)/ (elemental concentration in coal), which is greater than 10 for the non-volatile ele- ments. A much smaller ratio than 10 shows a high degree of volatilization. Natusch et aI. (1974) investigated different size fractions of fly ash, taken from eight coal fired power plants in the United States. He stated, that Pb, T1, Cd, Ni, Cr, Zn, and S are generally concentrated in the small particles. He proposed volatilization during com- bustion, and adsorption or condensation of these elements onto the small particles. The elements Mg, A1, Si, V, Mn, and Fe show similar, but much less well defined trends, K, Ca, Ti, Cu, and Bi show no convincing evidence of a correlation of their concentration with particle size. In summary, the enrichment of several elements in the samples can be caused by selective volatilization of the elements or their com- pounds, due to their low vapor pressure, and by small particle size. Vaporization is most important for Ag, Cd, Hg, T1, and Bi and the effect of particle size for Ni, Cr, Zn, chlorides and sulfates.

Sulfur reaches the atmospheric environment not only as sulfate, but also as SOx in the gaseous state. The sulfur compounds originate from the stepwise oxidation of sulfides in the coal.

2.3.3. Combustion of Refuse

Singh Dev (1972) found in combustion products of domestic and industrial refuse the following ranges of concentrations of elements (weight percent): Na, K, Ca, Pb(?)> >10~; Mg, Si, A1, Fe, Ba, Zn 1 to 10~; Ti, Cr, Cu 0.1 to 1~, Mn, V, Cd 100 to 1000 ppm; Ni, Bi, Mo 10 to 100 ppm. These elements generally form sulfates and chlorosulfates. Variable contributions are expected from these sources to the atmo- spheric transport of Bi, Cd, Pb, and other volatiles, and to the accumulation of Zn, Ba, Cr, and Cu in the residue. In addition Na, K, and Ca will be accumulated in rainwater. Molybdenum is as volatile as fluoride, which is generated by the combustion of polytetrafluorethylene and polyvinylchloride.

456 HANS RUPPERT

2.3.4. Fertilizers (Table IV) and Road Salts

Fertilizers add P, Ag, Ca, K, Mg, Na, and C1 and road salt contribute mainly Na, K, Mg, and C1 to the soils. Immediate influence on the composition of the sample is not expected, because fertilizing is preferentially applied in the spring or fall and spreading road salt is done in the winter. Over an extended period they modify soil composition.

2.3.5. Organic Matter (Table V)

Half of the samples consists of organic matter (Table I). Table V shows the parts of the elements remaining after ashing in percent of the total amounts of elements. They range between the contribution of plants and insects. The high phosphorous content of insects is conspicuous. Although insects were removed from the samples, some elements such as P, K, Zn, Li, Na, and Cu might be released into solution from their decaying bodies. Land plants can raise the content of Mn, K, P, Ca, and Rb.

Despite protection, contamination by bird excrement changed the composition of one of our samples. This considerably augmented the concentration of Zn and P, and soluble K, C1, Na, Si, and Mg.

3. Correlation Coefficients (Table VI)

The uniform composition of the residue with regard to the elements Si, A1, K, Rb, Ti, Na, Ni, Mg, Fe, Ca, Ba, V, Li, and T1 is noticeable, whereas Ag, Cd, Cu, P, Zn, Bi, Mo, Cr, and Pb are inhomogeneously distributed among the samples. (see ranges of concentration in Table IV). The constant concentration of the first group of ele- ments implies high linear correlation coefficients (R>0.90) of the absolute values (Table VI). The coefficients are not calculated for Hg, Bi, Cd, and T1 in the residue, because only seven determinations were made. The homogeneity of the residue is caused by transportation and sedimentation of the undissolved elements in constant weight proportions. Lithium (low reproducibility), Zn, and Cr have similar trends. Lead is highly correlated with V and Mo, referring to their origin from gasoline or fuel oil, but a corresponding high coefficient with Ni is lacking (R about 0.63). The remaining elements do not correlate with each other.

Reasonable coefficients among the elements dissolved in rainwater are found only between K and Na, Cu and Si, and between Mn, P, Ca, and A1. The last four elements have pronounced correlations with the amounts of elements in the residue. Lack of significant correlations of the remaining elements is due to strongly changing condi- tions during incorporation, transportation, and sedimentation of the elements in the atmospheric environment and to the interaction of solids with water.

It is difficult to explain the excellent correlation coefficients of Ti, Mn, Fe, Ba, V, and Ni, elements which are enriched by factors of 2 to 3 in comparison to shale. No soil around G6ttingen shows such concentrations of Ti, Mn, and Fe (Ffichtbauer, 1950; Echle, 1961). Probably, most of these elements are bound to anthropogenically

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generated phases, which are mixed with naturally occurring minerals in a uniform dust. The extreme concentration variations and the lack of correlation between the elements of the second group suggest specific local and variable emissions or distinct properties of the aerosols: As mentioned above, the elements Ag, Cd, Hg, Pb, and T1, and Ni, Cr, and Zn are preferentially transportated in the form of the finest aerosols and particles and support different conditions of sedimentation. Peirson et al. (1973) established analyzing samples from the English Lake District, that Cu, Pb, Zn, Mn, V, and Cr have lower dry deposition velocities and washout factors than Na, C1, Ca, A1, Fe, and Ni.

4. Influences of Local Factors and Sampling Time

In the center of G6ttingen where the absolute amount of most elements is highest in comparison to surrounding sampling stations, we found the lowest concentrations of the toxic elements Ag, Bi, Cd, Cu, Mo, Pb, Hg, and Zn in the residue. One possible explanation for this fact is the large amount of dust in the atmosphere from sweeping of the streets. The dust from the streets probably does not show the high concentration of the above cited toxic elements, because industrial emission is minimal in the center and traffic is restricted. The industrial area is characterized by concentrations of Cu and Cr, which are twice as high as those from other sites.

The elements Na, C1, K, H, and sulfate have higher concentrations in the rainwater, if the amount of precipitation is low. Only the first rain is effective in washout, whereas the later rain dilutes the samples. The total amounts of dissolved elements are similar in both sampling periods (Table I). Precipitation effects on the composition of the insoluble residue are neglegible.

The acidity of the rain is reduced by the interaction with dust carbonate of the GSttingen area.

5. Comparison with Data from the Literature (Table VII)

The influence of different sources on sample composition can be derived from com- parison with different sampling sites (Table VII). Four relatively unpolluted sites in England, the U.S.S.R., Japan, and the U.S.A. and one relatively polluted site in the U.S.A. were chosen. The samples from this work, from Japan, Soviet Union, and England are increasingly controlled by the sea (Na, C1) and decreasingly by land (A1, Ca, Fe, K, Mg, Mn, Rb, Si). Anthropogenic sources could completely dominate the two natural sources of airborne trace elements.

Buffalo U.S.A. is a center of heavy industry. The high Al-normalized enrichment factors of Pb, Ni, Mo, and V suggest, that the combustion of petroleum products is 10 to 90-times as high as in G6ttingen. Also Ag is 50-times enriched, Mn, Cu, and Fe are increased 3-times, C1 and Na are diluted.

In contrast to Buffalo, the air in the English Lake District is only slightly polluted from distant heavy industry more than 30 km away. The concentrations of the anthro-

GEOCHEMICAL INVESTIGATIONS ON ATMOSPHERIC PRECIPITATION

TABLE VII

Data on rainwater and air dust composition from literature and from this work

459

Rainwater samples (ppb) GSttingen Lake Northwest Japan z Quillayute, (,Germany) District 1 of the Washington (this work) (England) U.S.S.R9 (U.S.A.) 4

Air sam- Ratio pies Buf- (A1- falo, N.Y. normal- area 5 ized) (U.S.A.)

Dissolved Total* Total* Dissolved Dissolved Dissolved (/zg m -3) A B C D E F G G/B

Ag >0.24 A1 89 1500 160 110 Ca 2620 3000 300 ~ 1200 970 Cd 0.50 0.58 < 18 CI 870 >870 4100 1400 1100 Cr >14 2.9 Cu 6.8 16 23 0.83 Fe 43 1440 200 49 b 230 Hg 0.04 1.5 <0.2 K 600 1000 200 a 700 260 Mg 280 670 200 a 1400 360 Mn 25 43 8.1 10.9 b Mo >0.44 0.06 Na 540 800 2300 1200 1100 Ni >3.6 <6 4.2 b P 230 350 14 Pb 5.4 35 39 8.0 b Rb >2.0 0.67 SO2-4 8800 >8800 3400 a 7400 4500 Si 7O 7000 830 V >4.7 1.4 Zn 48 71 85 4.2 pH 3.9 4.5 5.2

0.01 50 <140 2200 1

300 610 <0.49 <0.1 60 <2.9

0.4 70 3.0 < 10 3350 1.6

<0.1 12

0.19 220 3.5 10 <15

150 1150 1.0 500 <93

<0.1 4200 82

800 <12

* Total = amount of an element in the residue + dissolved amount of the element. Data f rom: 1 Peirson et al. (1973) (annual summary 1971); ~ Gorham (1955) (average from data of May to October).

Petrenschuk and Selezneva (1970) (collected in the northwest of the European part of the U.S.S.R., prob- ably before 1964); b Drozdova and Makhon'ko (1970) (collecting time 1 yr: 1968/69). 3 Sugawara (1967) (averaged from 300 samples). 4 Tanner et al. (1972) (collected April 1970). 5 Pillay and Thomas (1971) (average of 200 samples, collected during 1968/69).

pogen i c e l emen t s Cu, Pb, Zn, Ni , and (V) f r o m the L a k e Dis t r i c t agree la rge ly w i t h

the resul ts f r o m this work . On ly C r a n d H g are en r i ched in the air o f GS t t i ngen .

T h e l ead a n d sulfa te con t en t s in the samples f r o m the n o r t h w e s t o f the E u r o p e a n

t e r r i t o ry o f the U . S . S . R . a re j u s t as h i g h as in G6 t t i ngen . Sul fur ic ac id seems to be

n e u t r a l i z e d by c a r b o n a t e s as n o t e d by Ca a n d the inexp l icab ly h igh c o n t e n t o f Mg ,

w h e r e b y the p H is h ighe r t h a n in G6 t t i ngen .

460 HANS RUPPERT

The prec ip i ta t ion in the sampl ing sites in Japan is still c leaner: The elements Cu, P,

and Zn are more than eight- t imes lower c o m p a r e d with G6tt ingen. They may represent

b a c k g r o u n d values for the cont inenta l areas o f the nor thern hemisphere together

with the elements Ag, Cr, Cu, Zn, and Hg, which were de te rmined in a sample f rom

Quil layute, Wash ing ton U.S.A. . This sample is an example for extremely pure rain-

water with regarding to all invest igated elements.

Acknowledgements

I should like to thank Prof. K .H. Wedepoh l for suppor t and discussion of this in-

vest igation. M y colleagues have been of great help wi th analyt ical techniques. I am

indebted to D r R. L. Jacobson, who improved my English.

References

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