geochemical investigations on atmospheric precipitation in a medium-sized city (göttingen, f.r.g.)

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  • 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 550C 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 750C and atomiza- tion at 2400C 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 500C 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 origi