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Research Articles COS, CS 2 and SO2 in AL-Smelter Exhaust COS, CS2 and SO2 in Aluminium Smelter Exhaust - The Contribution of Aluminium Production to the Global COS Budget JJochen Harnisch, tReinhard Borchers, 2peter Fabian 1Max-Planck-Institut ffir Aeronomie, Postfach 20, D-37189 Katlenburg-Lindau, Germany 2Universit~it M/inchen, Institut fiir Bioklimatologie und Immisionsforschung, Hohenbachernstr. 22, D-85354 Freising-Weihenstephan, Germany Corresponding author: Jochen Harnisch, Max-Planck-Institute for Aeronomy, P.O.-Box 20, D-37189 Katlenburg-Lindau, Germany Abstract Measurements of carbonyl sulfide (COS) and carbondisulfide (CS2) were carried out on samples drawn from a smoke stack of an alu- minium smelter. Volume mixing ratios of 6 ppm COS and 0.1 ppm CS2 were measured for gases from the electrolysis unit that had pre- viously passed an A1203 fluid bed reactor and electrostatic precipi- tators. Specific emissions of 1.6 kg COS and 0.03 kg CS2 per ton of primary aluminium were found. Extrapolating from this particular smelter's conditions to a world mix specific COS emissions of about 4 kg/t(A1) are calculated resulting in emissionsof annually 0.08 Tg COS into the atmosphere due to electrolyticaluminium production in 1995. Besides the photochemical conversion of anthropogenic CS 2 aluminium production is established to be the second major industrial source of COS probably exceeding automotive tire wear's and coal combustion's contributions. Key words: carbonyl sulfide; carbondisulfide; sulfur dioxide; car- bon monoxide; stratosphere; sulfate aerosol; back- ground aerosol; ozone depletion; aluminium produc- tion; electrolysis; anodic gas; anode carbon; coal, sul- fur content; inert anodes; Hall-Htronlt process 1 Introduction Carbonyl sulfide (COS) is the only sulfur species that is lon- glived enough to reach the stratosphere through normal at- mospheric transport. In volcanic quiescent times its abun- dance thus controls the sulfur budget of the middle atmo- sphere, where COS is photochemically transformed into sul- furic acid (H2SO4) to constitute the stratospheric background aerosol (CRUTZEN 1976). This background ae- rosol influences the radiative properties of the stratosphere (LACtS et al. 1992) and also enhances chlorine activation via heterogenous reactions on its surface (HANSON et al. 1994). Since publication of the most recent data base on sinks and sources of COS (CHFN and DAVIS 1993) some major upda- tes were necessary indicating that strengths of different na- tural and anthropogenic sources and sinks of COS are still not well known. Automotive tire wear was identified as a major anthropogenic source of COS (Pos and BERRESHEIM 1993) possibly annualy contributing as much as 0.075 Tg (1 Tg = 1012g) to the total global COS emissions which are estimated to be of the order of 1.2 Tg (CHrN and DAVIS 1993). Another study (Ulsh6fer et al. 1995) indicated that the amount of COS emitted from the oceans is currently pos- sibly overestimated by as much as 15 %. Recently the question was raised whether emissions from alu- minium smelters could contribute significantly to the global atmospheric budget of carbonyl sulfide (HARNISCH et al. 1995 a). From older measurements (HENRY and HOLLIDAY 1957, HERGET 1981, BRANt)ON et al. 1992) the authors pre- dicted specific COS emissions between 1 and 8 kg/t(M) if all COS produced during electrolysis is emitted into the at- mosphere and not removed by subsequent waste gas treat- ment. To determine the amount of COS released into the environment more precisely it was crucial to carry out mea- surements on actual emissions of an aluminium smelter. 2 Measurements at an aluminium smelter 2.1 Sampling The samples analysed for this study were taken at a German aluminium smelter using prebake-technology (subsequently refered to as "smelter PB"). It has an annual capacity of 200,000 t of primary aluminium. Anodes with sulfur con- tents of 1 - 1.1% are used in electrolysis cells. The waste gases that are produced with a specific rate of 100,000 m3/t(A1) (STP) are humidified and subsequently passed through a fluid bed reactor with AI203 to remove hydroflu- oric acid (HF). Two electrostatic precipitators reduce dust emissions. For western standards smelter PB can be consi- dered as typical concerning size, technology and waste gas treatment. Flue gases (60 ~ after complete gas treatment were col- lected in electropolished stainless steel containers (8 liter) that had previously been evacuated. Air from well within the wa- ste gas line was transfered to the sample containers through a 1.2 m stainless steel tube and passed through a stainless steel filter to avoid the intrusion of dust. Three samples were taken at intervals of about 10 minutes. ESPR-Environ. Sci. & Pollut. Res. 2 (4) 229-232 (1995) ecomed publishers, D-86899 Landsberg, Germany 229

COS, CS2 and SO2 in aluminium smelter exhaust

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Research Articles C O S , C S 2 and SO2 in AL-Smelter Exhaust

COS, CS2 and SO2 in Aluminium Smelter Exhaust

- The Contribution of Aluminium Production to the Global COS Budget

JJochen Harnisch, tReinhard Borchers, 2peter Fabian

1Max-Planck-Institut ffir Aeronomie, Postfach 20, D-37189 Katlenburg-Lindau, Germany 2Universit~it M/inchen, Institut fiir Bioklimatologie und Immisionsforschung, Hohenbachernstr. 22, D-85354 Freising-Weihenstephan, Germany

Corresponding author: Jochen Harnisch, Max-Planck-Institute for Aeronomy, P.O.-Box 20, D-37189 Katlenburg-Lindau, Germany

Abstract

Measurements of carbonyl sulfide (COS) and carbondisulfide (CS2) were carried out on samples drawn from a smoke stack of an alu- minium smelter. Volume mixing ratios of 6 ppm COS and 0.1 ppm CS 2 were measured for gases from the electrolysis unit that had pre- viously passed an A1203 fluid bed reactor and electrostatic precipi- tators. Specific emissions of 1.6 kg COS and 0.03 kg CS 2 per ton of primary aluminium were found. Extrapolating from this particular smelter's conditions to a world mix specific COS emissions of about 4 kg/t(A1) are calculated resulting in emissions of annually 0.08 Tg COS into the atmosphere due to electrolytic aluminium production in 1995. Besides the photochemical conversion of anthropogenic CS 2 aluminium production is established to be the second major industrial source of COS probably exceeding automotive tire wear's and coal combustion's contributions.

Key words: carbonyl sulfide; carbondisulfide; sulfur dioxide; car- bon monoxide; stratosphere; sulfate aerosol; back- ground aerosol; ozone depletion; aluminium produc- tion; electrolysis; anodic gas; anode carbon; coal, sul- fur content; inert anodes; Hall-Htronlt process

1 Introduction

Carbonyl sulfide (COS) is the only sulfur species that is lon- glived enough to reach the stratosphere through normal at- mospheric transport. In volcanic quiescent times its abun- dance thus controls the sulfur budget of the middle atmo- sphere, where COS is photochemically transformed into sul- furic acid (H2SO4) to constitute the stratospheric background aerosol (CRUTZEN 1976). This background ae- rosol influences the radiative properties of the stratosphere (LACtS et al. 1992) and also enhances chlorine activation via heterogenous reactions on its surface (HANSON et al. 1994).

Since publication of the most recent data base on sinks and sources of COS (CHFN and DAVIS 1993) some major upda- tes were necessary indicating that strengths of different na- tural and anthropogenic sources and sinks of COS are still not well known. Automotive tire wear was identified as a major anthropogenic source of COS (Pos and BERRESHEIM 1993) possibly annualy contributing as much as 0.075 Tg (1 Tg = 1012g) to the total global COS emissions which are

estimated to be of the order of 1.2 Tg (CHrN and DAVIS 1993). Another study (Ulsh6fer et al. 1995) indicated that the amount of COS emitted from the oceans is currently pos- sibly overestimated by as much as 15 %.

Recently the question was raised whether emissions from alu- minium smelters could contribute significantly to the global atmospheric budget of carbonyl sulfide (HARNISCH et al. 1995 a). From older measurements (HENRY and HOLLIDAY 1957, HERGET 1981, BRANt)ON et al. 1992) the authors pre- dicted specific COS emissions between 1 and 8 kg/ t (M) if all COS produced during electrolysis is emitted into the at- mosphere and not removed by subsequent waste gas treat- ment. To determine the amount of COS released into the environment more precisely it was crucial to carry out mea- surements on actual emissions of an aluminium smelter.

2 Measu remen t s at an aluminium smelter

2.1 Sampling

The samples analysed for this study were taken at a German aluminium smelter using prebake-technology (subsequently refered to as "smelter PB"). It has an annual capacity of 200,000 t of primary aluminium. Anodes with sulfur con- tents of 1 - 1 . 1 % are used in electrolysis cells. The waste gases that are produced with a specific rate of 100,000 m3/t(A1) (STP) are humidified and subsequently passed through a fluid bed reactor with AI203 to remove hydroflu- oric acid (HF). Two electrostatic precipitators reduce dust emissions. For western standards smelter PB can be consi- dered as typical concerning size, technology and waste gas treatment. Flue gases (60 ~ after complete gas treatment were col- lected in electropolished stainless steel containers (8 liter) that had previously been evacuated. Air from well within the wa- ste gas line was transfered to the sample containers through a 1.2 m stainless steel tube and passed through a stainless steel filter to avoid the intrusion of dust. Three samples were taken at intervals of about 10 minutes.

ESPR-Environ. Sci. & Pollut. Res. 2 (4) 229-232 (1995) �9 ecomed publishers, D-86899 Landsberg, Germany

229

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COS, CS 2 and SO2 in AL-Smelter Exhaust Research Articles

2.2 Analysis

Beginning 20 hours after collection samples were analysed at the Max-Planck-Institute for Aeronomy (MPAE). A cry- ogenic preconcentration from 5 - 8 cm 3 (STP) of the sam- ples was carried out prior to injection into the gaschroma- tographic system. The J & W DBl-column (60 m x 0.32 mm/1/~ coating) of the VARIAN 3400 gas chromato- graph was temperature programmed from - 6 5 ~ to 175 ~ up with 8 ~ Air components were identified and quantified with a VARIAN iontrap mass spectrometer (Saturn II) simultanously acquiring ion masses 5 0 - 3 0 0 . Apart from sulfur species a variety of aromatic and polya- romatic hydrocarbons was detected but not quantified. With a reproducibilty of better than _ 10 % COS and CS2 were detected on ion masses 60 and 76 respectively. The detec- tion limit for both COS and CS2 was about 100 pptv from 5 cm 3 (STP) of sample air. Measurements were refered to a working standard that had previously been calibrated for COS with an absolute precision of _+ 10 % (KOURTIDIS et al. 1995). For CS2 the same specific sensitivity was assumed as for COS. CS2 values are therefore preliminary. During the two weeks of repeated analysis the stored samples sho- wed stable mixing ratios for COS and CS 2 within the un- certainties of our measurements. There was no significant variation of COS mixing-ratios from sample to sample. Ta- ble 1 lists our results for COS and CS 2 together with other parameters provided by the operators of smelter PB. SO 2 is periodically determined by means of a manual wet chemical method (aq. H 2 0 2 ) with an overall uncertainty of about +- 15 %. Errors of values for HF and CO are estimated to be of the same magnitude.

Table 1: Flue gases f rom smelter PB after waste gas treatment. COS and CS 2 from own measurements , data on HF, CO and SO 2 were provided by the operators of smelter PB

Species mixing rat io concentrat ion specif ic emission [ppmv] [mg/Nm 3] [Kg/t(AI)]

3OS 6 16 1.6

3S 2 0.1 0.3 0.03

SO 2 35 100 10

HF 0.45 0.4 0.04

.30 800 - 960 1000 - 1200 100 - 120

2.3 Comparison with Older Measurements

In our earlier work on COS emissions from aluminium- smelters (HARNISCH et al. 1995 a) we based our prognosis on older measurements (HENRY and HOLLIDAY 1957, HER- GET 1981, BR~NDON et al. 1992). All of them indicated that COS is produced in substantial amounts during aluminium production. A direct quantification of specific COS emissions (kg(COS)/t(A1)) was difficult for neither study mentioned typical air flows, analytical details, characteristics of pro- duction technology (e.g. sulfur content of anodes). The ef- fect of dry waste gas cleaning was also unknown.

The results of different measurements on exhausts from alu- minium production are compiled in Table 2. Concerning ab-

solute concentrations of species they show a confusing pic- ture. This can be partly attributed to different dilution fac- tors of original anodic gases that apply for each location and technology. Therefore we used CO/COS values in our pre- vious work in order to obtain comparable values. The va- lues from the oldest study (HENRY and HOLLIDAY 1957) had to be evaluated with special care: The total amount of sul- fur (CS2, COS and SO2) found in their samples is unreali- sticly low compared to carbon monoxide. This has proba- bly to be attributed to losses inside glass sampling contai- ners or some severe problems with calibrations.

Table 2: COS, CS 2, SO 2 and CO in aluminium smelters' waste gases

Study

Henry & Holliday 1957 (pure anodic gases)

Herget 1981 (pot room)

Brandon et al. 1992 (pot gases)

This work (flue gases)

COS ]CS 2 SO 2 CO mol- [ppm] i[ppm] [ppm] [ppm] ratio

soft COS

25 n.d. 60 110000 ! 2.4

0.02 - 0.5 4 25

0.35 - - 31 -

6 0.1 35 920 6

mol- ratio CO/

I COS

4500

200

90

150

2.4 The Sulfur Budget - Missing Sulfur

Usually SO 2 is the only sulfur species measured in smelter emissions. Reduced sulfur species such as COS and CS 2 were thus usually not considered in sulfur budget calcula- tions even though about 20 % of the total sulfur mass was omitted that way. Knowing the total sulfur input into the ovens and monitoring the SO2 emissions with sufficient ab- solute precision ( _ 5 %) it should be possible to roughly estimate the sum of reduced sulfur emissions from other smel- ters with no extra measuring effort.

3 A l u m i n i u m Electrolysis and its Sulfur Chemis t ry

Aluminium is today almost exclusively produced in the Hall- H6roult process in which molten cryolite (Na3A1F6) is used to dissolve A1203 at temperatures between 940 ~ and 980 ~ In an eletrolytic cell consisting of graphite catho- des and carbon anodes A1F4-from the bath reacts according to E1 at the cathode. At the same time anode carbon is oxi- dized in reaction E2. During electrolysis Al203 is continu- ously added to sustain an A1203 content of the bath of above about 2 %.

AlF 4- + 3e- ~ A1 + 4F- E1 C + 202. -~ CO2 + 4e- E2

The real situation is of course much more complicated in- volving more ions and reactions. For further details see e.g. GRJOTHEIM and WELCH (1988). For the purpose of this work it is important to keep in mind that any aluminium produced in the Hall-H6roult process requires roughly an equal number of moles of carbon for the anodic reaction E2. As part of commercial carbon anodes sulfur is introduced

230 ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995

Page 3: COS, CS2 and SO2 in aluminium smelter exhaust

Research Articles COS, CS2 and SO2 in AL-Smelter Exhaust

into the electrolytic system taking part in complex non equi- librium chemistry. The following system of reactions (E3-E12) was used by OEDEGARD et al. (1985) to characte- rize the sulfur chemistry of a Hall-H&oult electrolysis cell.

S 2 + 4CO 2 ~-~ 4CO + 2SO 2 E3 CS2 + CO2 ~ 2CO + $2 E4 2COS ~ 2CO + S 2 E5 COS + 2CO 2 ~ 3CO + SO 2 E6 CS2 + C02 ,-~ 2COS E7 COS + H 2 ~ H/S + CO E8 H2S + 3CO2 ~ 3CO + SO 2 + H20 E9 2H2S +CO2 ~-~ CS2 + 2H20 El0 2H 2 + S 2 *-* 2H2S E 11 H 2 + CO 2 ~ H20 + CO E12

3.1 Framework for Emission-Prediction

The range of suitable thermodynamic conditions for efficient electrolytic production of aluminium is quite narrow. We are therefore confident that the partitioning of sulfur species in exhausts from aluminium smelters in first approximation can be satisfactory described as a function of available sulfur. The only parameters that we allow to vary from smelter to smelter is the sulfur content r s of anodes and the required amount of anode carbon m Aper ton produced together con- stituting the specific sulfur input m s . In the theoretical part of their study on sulfur compounds in anodic gases OEDE- GAP.D et al. (1985) found COS emissions to depend linearly on the sulfur content r s of the anodes while CS 2 emissions grew quadratically with increasing sulfur content. Together with the appropriate constants kco s and kcs 2 derived from measurements at smelter PB we now have a tool to calcu- late emissions of COS and CS2 from individual smelters and also for a world-mix of technologies. The following expres- sions E13 and E14 are used for a first estimate of specific COS and CS2 smelter emissions of meo s and mcs 2.

mcos=kco s * ms=kco s * m A * r s E13 m c s 2 = kc s 2 * m A * rs 2 E 14

Knowing tacos, mcs2, m A and r s for smelter PB we calculate the missing constants:

kcos=0.36+O.05 kcs2 = 0.63 + 0.19 E15 a./b.

3.2 Typical Sulfur Input into the System

The specific sulfur input m s into the electrolytic system of an aluminium smelter depends on the sulfur mass content r s of the carbon anodes and the specific amount of anodes m a required to produce a given amount of aluminium. Car- bon anodes are manufactured from petroleum coke or pitch coke (70 - 85 %) and a coal-tar or petroleum pitch used as binding pitch (15 - 30 %). The sulfur content of the anodes can thus vary considerably according to composition and ori- gin of raw materials. Following OEDEGARD et al. (1985) we use an average of r s = 2.5 % for global calculations. This value has an uncertainty of about 20 % which will of course propagate into emission calculations. The specific anode con- sumption m. is much less variable depending mainly on the

power efficiency of a smelter. The anode consumption m a is today typically between 410 and 500 kg/t(A1). We used a value of 450 kg/t(A1) for the world mix. Table 3 shows a compilation of the above values for smelter PB and the esti- mated world-mix.

Table 3: Data on sulfur inputs for smelter PB and estimate of world average

Smelter PB World Mix

sulfur content of anodes r s [%] 1.05_+0.05 2.5+0.5

specific anode consumption m A 430+ 10 450_+20 [kg/t(AI)]

specific sulfur input m s [kg/t(AI)] 4 .5+0.2 11.3_+2.3

specific COS emissions [kg/t(AI)] 1.6 -+ 0.3 4 _+ 1

specific CS 2 emissions [kg/t(AI)] 0.03_+0.02 0.2_+0.1

4 Current and Future Impact on the Atmospheric Budget of COS

Under the assumption of constant partitioning of sulfur spe- cies in the exhaust from Hall-H&oult cells we calculated the global annual COS emissions from aluminium production as a function of average specific sulfur input and annual pro- duction. The results are plotted in figure i which can be used as a tool to estimate COS emissions under different condi- tions.

For 1995 we obtained COS emissions of 0.08 Tg and 0.004 Tg of CS2 released into the atmosphere for the 20 mio tons of primary aluminium produced. CHIN and DAvis (1993) estimated the global annual input of COS into the atmo- sphere to be 1.2 Tg with an anthropogenic contribution of about 30 %. In 1995 aluminium production was thus re- sponsible for about 6 % of all COS emissions and for about 20 % of the anthropogenic share. If aluminium production sustains an annunal growth of + 4 % until 2030 resulting in an annual production of 80 mio tons aluminium an input of 0.32 Tg COS into the atmosphere is to be expected per year.

0.35

~0.30

o~ 0.25 .~ 0.20

0.15 o

o 0.10

0.05 <

0.00

a n n u a l A I -

p r o d u c t i o n : . - " . I .

. . . . . . 8 0 m i o t . . " . / " " ~ - ' I "

. . . . 6 0 m i o t ' - " - ~ "

. . . . 4 0 m o t ." . ~ " ....- �9 ~ "

2 0 m i o t . " , . " i . . ~ -

/ ' i . ' t - .2----'~ 1~

5 10 15 20 25 Average specific sulfur input [ kg / t(AI) ]

Fig 1: Current and future COS emissions from a luminium product ion as function of the annual world product ion and the average specific sulfur input into the electrolysis cells. An estimate for the year 1995 is indicated wi th according error bars

ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995 231

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COS, CS2 and SO2 in AL-Smelter Exhaust Research Articles

5 S u m m a r y and Conclusion

5.1 Summary

With this work we could show that aluminium production is probably the most important direct industrial source of carbonyl sulfide. About 20 % of the total sulfur mass intro- duced into the electrolysis units via anode carbon is emitted as reduced sulfur components. A simple framework was de- veloped to estimate current and future emissions of COS from aluminium production. Using data from GRJOTHEIM and WELCH (1988), HARNISCH et al. (1995 b) and this study a compilation of average specific trace gas emissions from aluminium electrolysis is obtained as listed in Table 4.

Table 4: Estimates of global averages (1995) of specific trace gas emis- sions from aluminium electrolysis (without power generation or production of any raw materials). Actual emissions of in- dividual smelters may vary considerably from case to case

Species CO 2 CO SO 2 COS CF 4 CS 2 C2F 6

Spec. Emis. 1400 150 18 4 0.75 0.2 0.11 [kg/t(AI)] (+200) (_+50) (+4) (_+1) (+0.05', (_+0.1) (_+0.01)

5.2 Evaluation of COS Emissions

There are still many open questions concerning the global sulfur budget of the atmosphere. During twenty years of in- tensive research on sources and sinks of COS many impor- tant processes have been discovered. A more complete un- derstanding of the atmospheric sulfur cycle with its coup- ling to the biosphere, the hydrosphere and the geosphere will hopefully be gained in the future. Today it is not possible to scientificly assess the atmospheric effects of anthropoge- nic COS emissions. There is not much doubt on the other hand, that anthropogenic emissions have about doubled the annual input of COS into the atmosphere increasing the avai- lability of sulfur in regions and heights that were still quite unperturbed from anthropogenic influences. Even if this si- tuation is yet not proven to be harmful it should definitely be considered undisirable.

5.3 Further Research

Aside from the need for further research on atmospheric COS and its impact on stratospheric and tropospheric processes we suggest the following issues to be treated in the near future:

1. Estimation of a reliable value for the specific sulfur input for a world mix of smelters

2. Re-evaluation of old SO2 emission data and sulfur input values to calculate reduced sulfur emissions with no ex- tra measuring effort

3. Measurement of COS emissions at other smelters e.g. S6derberg-smelters and smelters using anodes with high sulfur contents

4. Measurement of possible COS emissions from anode pro- duction due to coal pyrolysis

5. Research on the parameters controlling COS production in aluminium smelters

6. Research on possibilities of catalytic destruction of COS in waste gases

7. Evaluation of economic costs of a reduction of sulfur con- tents of anodes

8. Intensive research and demonstration projects of inert anode electrolysis

6 References

BRANDON, R. W.; R. L. SCHLOSSER; R. H. KAGANN: FTIR open path site survey of toxic gas emissions at an aluminum smelting plant, Air and Waste Management Assoc., 85 th annual meeting, paper-92- 83.03, 1992

CHIN, M. ; D. D. DAVIS: Global sources and sinks of COS and CS 2 and their distributions, Global Biochem. Cycles, 7 (2), pp. 321 - 337, 1993

CRUTZEN, P. J.: The possible importance of CSO for the sulfate layer of the stratosphere, Geophys. Res. Lett., 3, 73-76, 1976

GRJOTHEIM, K.; ]3. J. WELCH: Aluminium smelter technology, 2 nd edi- tion, Ahminium-Verlag, D6sseldorf, 1988

HANSON, D. R; A. R. RAVISHANKARA; S. SOLOMON: Heterogenous re- actions in sulfuric acid aerosols: A framework for model calcula- tions, J. Geophys. Res., 99, D2, pp. 3 6 1 5 - 3 6 2 9 , 1994

HARNISCH, J.; R. BORCHERS; P. FABIAN; K. KOURTIDIS: Ahminium Pro- duction as a Source of Atmospheric Carbonyl Sulfide (COS), Env. Science. Pol. Res., 2 (3), 229-232 , 1995 a.

HARNISCH, J.; R. BORCHERS; P. FABIAN: Estimation of tropospheric trends (1980-1995) for CF 4 and C2F 6 from stratospheric data, International Society for Optical Engineering/European Optical So- ciety, Europto-Series, Vol. 2506, pp. 384 -393 , 1995 b

HENRY J. L.; R. D. HOLLIDAY: Mass spectrometric examination of anode gases from aluminum reduction cells, J. of Metals, pp. 1384- 1385, 1957

HERGET, W. F.: Measurement of gasous pollutants using a mobile Fourier transform infrared (FTIR) system, The International Society for Optical Engineering, Vol. 289, pp .449-456 , 1981

KOURTID1S, K.; R. BORCHERS; P. FABIAN; J. HARNISCH: Carbonyl sul- fide (COS) measurements in the Arctic polar vortex, Geophys. Res. Let., 22, No.4, pp. 393-396 , 1995

LACIS, A; J. HANSEN; M. SATO: Climate forcing by stratospheric aerosols, Geophys. Res. Let., 19, No. 15, pp. 1607 - 1610, 1992

OEDEGARD, R.; S. ROENNING; A. STERTEN; J. THONSTAD: Sulphur con- taining compounds in the anode gas from ahminium cells, Light Metals, pp. 6 6 1 - 670, 1985

Pos, W. H. and H. BERRESHEIM: Automotive tire wear as a source for atmospheric COS and CS2, Geophys. Res. Lett., 20, pp. 815 - 817, 1993

ULSHOFER, V. S.; G. UHER; M. O. ANDtLEAE: Evidence for a winter sink of atmospheric carbonyl sulfide in the northeast Atlantic Ocean, Geophys. Res. Lett., 22, pp. 2601-2604, 1995

Received: Oktober 26, 1995 Accepted: November 10, 1995

232 ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995