Polluted snow in southern norway during the winters 1968–1971

POLLUTED SNOW IN S O U T H E R N N O R W A Y D U R I N G THE WINTERS 1968-1971 KARE ELGMORK, ARNE HAGEN & ARNFINN LANGELAND

Zoological Laboratory, University of Osto, Btindern, Osto 3, Norway

ABSTRACT

In recent years the snow in southern Norway has been laminated with conspicuous grey bands which were considerably more acid, had a higher electrical conductivity, larger amounts o f sulphur, heavy metals and other elements than the white layers o f the snow. These bands indicate a considerable airborne pollution with values of sulphur up to 8.5 mg/l and o f lead up to 98 l~g/1, and with p H values down to 3.25 in the melt wa ter. The chemical stratification in the snow was well preserved throughout the winter in areas with a coM climate. A regional stud),' of the snow in late winter may thus give information o f the distribution o f airborne pollution. The acidity and contents o f chemical substances in the snow was too high and found over too wide an area to have been produced in Norway. The pollution must have been brought in by low pressure systems from the great industrial and urban areas in western and central Europe. INTRODUCTION

An increase in the acidity of the precipitation in Scandinavia over the past decades is now a well-established fact (Od6n, 1968, 1969, 1971). So far, published results of the chemistry of the precipitation in Scandinavia have been presented mainly as monthly and even yearly means. Little attention has yet been given to individual rain- and snow-falls. Several snow-falls during past winters in southern Norway have attracted public attention for their dark, grey snow. Sections through the snow cover in late winter showed layers with grey and white zones (Fig. 1). Measurements of pH and electrical conductivity in the various zones were found to be closely correlated with the colour of the snow, the grey bands being more acid and with a higher conductivity than 41

Era:iron. Pollut. (4) (1973) pp.

41-52--~) Applied Science Publishers Ltd, England, 1973 Printed in Great Britain

42

Fig. 1.

KARE ELGMORK, ARNE HAGEN~ ARNFINN LANGELAND

Snow profile from Baerum, 10 Match 1969, showing grey, polluted layers. The uppermost and lowermost bands represent melting and refreezing. (Photo: K. Elgmork).

the white portions of the snow. It was assumed that relatively simple studies of the chemical composition of the snow would yield additional detailed information about the spread of atmospheric pollution in Scandinavia during the winter.

METHODS

Vertical sections were dug in the snow by means of a spade. The exposed and otherwise undisturbed cross-sections of the snow cover gave a snow profile. Samples of

POLLUTED SNOW IN SOUTHERN NORWAY DURING THE WINTERS

1968-1971

43

the snow were taken from different layers in the snow profile, using plastic teaspoons. In some cases samples were taken discontinually and included only a few centimetres of each snow layer. Such samples are marked on the accompanying diagrams by small rings. In other cases, samples were taken continually, blocks of snow were brought in for analysis covering the entire snow layer. The first method will show more clearly the extreme values in each snow-fall, while the latter will give a more reliable mean for the whole snow cover. There was no difficulty in discriminating between grey, polluted layers and light grey layers caused by previous spells of warm weather (Fig. 1). Snow samples were melted in pyrex glass jars and warmed up to about room temperature. The melt water was stirred and allowed to stand for about 10 rain before the analyses were made. Acidity was measured electrically on a Radiometer pH meter 29 and, in some cases, also colorimetrically with a Hellige comparator for control. Only the pH values measured electrically are presented in this paper except for those from Fyresdal 1968-69 (Fig. 2). The electrical conductivity was measured on a Philips measuring bridge (PR 9501). The values are given as reciprocal micro-ohms per cm (/~mho/cm) at 18°C. The symbol for this value is ~"18.

The winter 1968-69

In the winter of 1968-69 several snow-falls with grey snow occurred in southern Norway (Fig. 1). The snow that fell in the night between 4 and 5 January 1969 was especially noteworthy and was clearly contaminated over large areas of southern Norway. Snow profiles were photographed and analysed in March 1969 for pH and ~:18 in several places in southern Norway (Fig. 2). Laminated snow with grey layers was present in all sampling places. Except for Baerum, the sampling places are distant from industrial plants or urban areas. Vassfaret, Fyresdal, and Vinje are, for example, all situated in remote areas with very little habitation. It is therefore obvious that the snow pollution does not originate in the local environment. There was very close correlation between the greyish colour of the snow and its acidity and conductivity. With very few exceptions, the darkest layers showed the lowest pH and highest x t 8 values. With a difference of only a few centimeters in the snow profile, there were often marked differences in acidity and conductivity (Fig. 2). This indicates that the layers of snow are well preserved and leaching from one layer to another must be negligible. Other observations point in the same direction. The diagrams in Fig. 2 show that the layers nearest the ground are white and show low values of acidity and conductivity in all areas investigated. This indicates that the snow from late autumn

44

KARE ELGMORK, ARNE HAGEN, ARNFINN LANGELAND

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Analyses o f snow profiles, 1968-69. Values from 5 January constitute the base line for the arrangement o f the figures.

POLLUTED SNOW IN SOUTHERN NORWAY DURING THE WINTERS 1968-1971

45

and early winter are less polluted than the snow from middle and late winter and that leaching f r o m the upper to lower layers during the winter is insignificant. By comparing the pattern of the grey layers and the form of the curves, there was no difficulty in tracing corresponding layers over large areas. Note, for example, the similarity in the pattern of layers in the snow between Blaker, Vassfaret, and Fyresdal in Fig. 2. The layer from 5 January 1969 was easily recognisable and this layer forms the base for the arrangement of the diagrams and snow profiles in Fig. 2. By means of meteorological records, other layers can also be dated. It is, however, more reliable to study the snow in detail when it falls, as will be shown in the next section. The p H and ~:la values in the grey layer from 5 January 1969 are plotted on Fig. 3. The p H values in this layer varied between 3.8 and 4-8 over large areas of

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46

KARE ELGMORK, ARNE HAGEN, ARNFINN LANGELAND

southern Norway. The ~c18 values were mostly between 50 and 80. One value, from Baerum, was above 100. The three highest values were all from localities close to the city of Oslo. An additional, local, pollution from this urban area of about half a million people therefore seems very likely. The melt water from the grey layers of snow was clearly contaminated, e.g. the water from the layer of 5 January 1969 in Vassfaret was milkish grey and the walls of the jars were coated by a film of an oily, dark substance. Some chemical components in two of the snow profiles are presented in Table 1 TABLE 1 CHEMICAL COMPONENTS OF TWO DARK SNOW LAYERS (ANALYSES BY A. BOYUM)

Place

Sampling date

Date of snowfall

Total hardness CaCO3 in mg mg/I

SO4

1968-69

Na

K

CI

mg/I

mg/l

mg/l

mg/I

CaCO 3/l Vassfaret Baerum

10 March 1969 November 1968 10 March 1969 5 January 1969

3"09

1.20

6"1

2"44

0-37

7.3

6.00

2.40

25"4

3"66

0'50

10.8

The winter 1969-70 This winter showed the same phenomenon of laminated light and dark bands of snow over southern Norway as in the previous winter. Snow profiles were analysed from three of the previous stations and a new station, Rondane (National Park), was included in the programme (Fig. 4). The results were basically similar to those obtained in the previous winter. There was a close correspondence between grey bands and high acidity and conductivity, the highest values being obtained in the darkest snow layers. The snow nearest the ground showed the smallest values, as in the previous winter. The northernmost station, Rondane, showed fewer grey bands than the other stations. The snow was relatively uniform up to about 75 cm above the ground. This station is situated farther to the north, and fewer snow-falls of polluted snow might have reached the area. It is also situated higher (850 m) than the other stations and relatively more snow with less pollution might have fallen in late autumn.

Reliability test To check the reliability of the snow profile method, acidity and conductivity of the snow were measured immediately after each snow-fall at the Blaker station east of Oslo and compared with the results from the profiles taken later in the winter.

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Analyses of snow profiles 1969-70. The profile from Skrim was analysed on two dates, the lowermost on 31 January and the uppermost on 30 March.

48

KARE ELGMORK, ARNE HAGEN, ARNFINN LANGELAND

The results are shown in Fig. 5. The curves show a considerable variation in pH, h:l 8, and S of the same size order and with the same pattern as found in the snow profiles from Blaker and other areas. This shows that the variations in the profiles are primarily due to differences between snow-falls and a possible dry fallout seems negligible. This is also substantiated by a snow sample taken on 21 March 1969 in a residential area in Baerum 12 km from the city of Oslo. The sample was taken in the upper cm of snow which had been undisturbed and exposed to the air for twelve days without precipitation. The temperature during this period was mostly Dates

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below 0°C. The analysis gave a pH value of 5.3 and a K~ s of 37. In comparison with the results presented in Figs. 2 and 3 this is one of the highest pH values observed in the whole series o f samples, indicating very little influence from dry fallout even so close to a city and with oil-heated houses in the sampling area. The snow profile from 20 March shows a clear correlation to the results obtained by simultaneous analysis. This snow profile from late winter gives a fairly good replica o f the variations in the different snow-falls. The discrepancies are partly due to the method of taking whole blocks of snow which will level out the extreme values. By comparing snow profile values with the simultaneous observations, a fairly reliable dating o f layers can be obtained. For instance, the similarity between Blaker and Skrim (Fig. 4) is evident, and the dark bands at Skrim can thus be dated reliably. By taking into consideration meteorological observations, bands and chemical constitution of the snow can be determined and dated over wide areas by means of only one snow profile study in late winter.

POLLUTED SNOW IN SOUTHERN NORWAY DURING THE WINTERS 1 9 6 8 - 1 9 7 1

49

Preservation of the chemical composition of the snow The Blaker station in the winter of 1969-70 presents good evidence for the stability of the chemical composition of the snow. As mentioned above, the snow profile from 20 March gave similar results to those from the simultaneous observations, and this is also true for the results from the snow profile of 12 April. The time between these dates was characterised by temperatures below 0°C and practically no changes took place in the chemistry of the snow (Fig. 5). The low values in the snow nearest to the ground are still maintained, showing that no leaching of ions had taken place even during this late part of the winter. It was only after a warm, rainy spell in the middle of April that the chemical differentiation of the snow was broken down on 19 April. The conductivity was now the same in all layers, while the pH still showed higher values in the layers nearest the ground. However, with the very low buffering capacity this result is of less significance. These results show that the lamination and chemical differentiation of the snow are preserved remarkably well if temperatures, on the whole, are below freezing point.

The winter 1970-71 During this period, grey, polluted layers in the snow were observed in southern Norway, as in previous winters. Only two snow profiles were analysed, one in Vassfaret on 20 February 1971 and one in Skrim on 13 March. In addition to acidity and conductivity, the snow was analysed for certain heavy metals and some other elements. The results are given in Table 2. In Vassfaret exceptionally high values of all components analysed were found in the grey layer of snow, 74 cm above the ground, that fell on 15-16 February 1971. Also, the 70 cm-layer at Skrim showed very high values. These results show that considerable amounts of heavy metals are deposited by precipitation in southern Norway.

CONCLUSIONS AND DISCUSSION

The pH and ~ci 8 measurements are unspecified and do not give information of the substances causing the high values observed. There is, however, considerable additional information available which suggests that sulphuric acid plays an important role. First, Figs. 4 and 5 show a very close correlation between pH and sulphur content, the two curves following each other in all details. In addition, in 1970 the largest sulphur value was obtained in the sample with the lowest pH value (Fig. 5).

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51

It is therefore r e a s o n a b l e to c o n c l u d e t h a t both acidity a n d conductivity are m a i n l y c o n t r o l l e d by the a m o u n t s o f sulphuric acid. This conclusion is also s u p p o r t e d by the general t r e n d o f increasing a m o u n t s o f sulphur in the p r e c i p i t a t i o n over S c a n d i n a v i a (Od6n, 1968, 1969, 1971). T h e grey b a n d s in the snow, the high acidity a n d conductivity, high contents o f sulphur, heavy metals a n d o t h e r substances indicate a considerable p o l l u t i o n o f the air a n d p r e c i p i t a t i o n in s o u t h e r n N o r w a y in the winter. T h e high values f o u n d in r e m o t e places, far a w a y f r o m industrial a n d u r b a n areas, show t h a t the p o l l u t i o n is t r a n s p o r t e d over wide areas. T h e r e is little v a r i a t i o n f r o m y e a r to y e a r in p H a n d ~: 1s, as shown by the m e a n values presented in T a b l e 3.

TABLE 3 MEAN VALUES OF ACIDITY AND CONDUCTIVITY

Locality Fyresdal Skrim Baerum Blaker Vassfaret Rondane A

1968/69 A B 4"74 -4'35 4"48 4"58 --

--. ----

pH 1969/70 A B

1970/71 A B

1968/69 A B

4'12 4-08 4 - 6 7 4"62 - 4.04 3'97 . . . . . . . . 36"7 4"14 ---22"0 -4-20 4"41 - 20"3 4'18 4 - 1 8 . . . .

-. ---

x18 1969/70 A B

1970/71 A B

26'4 23"9 11.7 11.4 31 '5 29.1 - -. . . . 29.0 -----17.9 -21-1 16.9 - --

Arithmetric mean, B = Arithmetric weighted mean according to Od6n (1968, Table 8, p. 68)

T h e a m o u n t s o f pollution, as i n d i c a t e d by the similarity o f the p a t t e r n o f the snow profiles over large areas, are o f a m a g n i t u d e t h a t c a n n o t be a c c o u n t e d for by N o r w e g i a n activities. T h e low p o p u l a t i o n density, few industrial c o n c e n t r a t i o n s a n d few a u t o m o b i l e s in N o r w a y c a n n o t give such high values o f p o l l u t a n t s such as s u l p h u r a n d lead as are f o u n d in the snow in s o u t h e r n N o r w a y . These substances m u s t have been b r o u g h t in with the p r e c i p i t a t i o n f r o m the large industrial a n d u r b a n areas in western a n d central E u r o p e , occasionally also f r o m eastern E u r o p e . The l a m i n a t i o n f o u n d in the snow is caused by different m e t e o r o l o g i c a l situations a n d different routes followed by the low pressures as, for example, shown by Od6n (1971). The snow profile m e t h o d can be useful in a d d i t i o n to the m o r e r o u t i n e observations t a k e n at fixed stations. I n areas with a n i n l a n d climate with long, cold, winters a n d relatively large snow covers as f o u n d in central Scandinavia, this m e t h o d will be especially useful. A series o f snow profiles a n a l y s e d in late winter will, with relatively little effort, give valuable i n f o r m a t i o n on the chemical c o m p o s i t i o n o f the precipitation t h r o u g h o u t the w h o l e winter. A n e x a m p l e o f such a study is the snow transect across eastern a n d central S c a n d i n a v i a by Bergholm in M a r c h 1970 (Od6n, 1970).

52

KARE ELGMORK, ARNE HAGEN, ARNFINN LANGELAND ACKNOWLEDGEMENTS

We are obliged to Professor Dr Svante Od6n, Institutionen f6r markl~ira, Lantbruksh6gskolan, Uppsala, for stimulating discussion of methods and results. We are also grateful to Professor Dr David Klein, University of Alaska, College, Alaska, for criticism of the manuscript. For analysis of melt water from the snow we are thankful to the following persons and institutions: Fil. lic. Johan Bergholm, Institutionen f6r markl~ira, Lantbruksh6gskolan, Uppsala, Cand. real. Anders Boyum, Department of Limnology, University of Oslo, and to the Norwegian Institute for Water Research (NIVA), Oslo. The following persons have most kindly supplied photographs of snow profiles or samples of melt water: Mr Vegard Blakar, Mr Oivind Hagen, Cand. real. Karstein Lied, Cand. real. Ivar Mysterud, and Cand. real. Eivind Ostbye. For assistance in the field and in the laboratory we are thankful to Cand. real. Jon Arne Eie and Cand. real. Gunnar Halvorsen.

REFERENCES ODI~N, S. (1968). Nederbb'rdens och luftens fOrsurning~dess orsaker, pdrlopp oeh verkan i olika milj6er. Ekologikommitt6n. Bull 1, Statens Naturvetenskapliga Forskningsrad, Stockholm, 86 pp. (Duplicated). ODIN, S. (1969). Regionala aspekter pa milj6st6rningar. Vann, 4, 93-112. ODIN, S. (1970). Skogsn~ingen och miljovarden. Svenska SkogsF6r. Tidskr., 68, 314-5. ODIN, S. (1971). Nederb6rdens f6rsurning---ett generelle hot mot ekosystemen. In Forurensning og biologisk miljovern, ed. by I. Mysterud, 63-98. Oslo University Press, Oslo.