INTENSIVE MEASUREMENTS OF ATMOSPHERIC MERCURY

 

IN ANTARCTICA

 

 

SPROVIERI, F. ANDand PIRRONE, N.

CNR-Institute for Atmospheric Pollution, c/o: UNICAL, 87036 Rende, Italy

 

 

ABSTRACTbstract

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Field measurements to evaluate the concentrations of gaseous and particulate mercury in the Antarctic troposphere and its spatial distribution, were performed during an intensive measurement campaign carried out from November 5th to November 22th 1999 at the CNRItalian- Antarctic Station located in Terranova Bay (74°41’42” South, 164°07’23” East).  Total Gaseous Mercury (TGM) samples were taken every 24 hours with manual Au-cartridges at a flow-rate of 0.3 lLpm and analysed by Cold Vapour Atomic Fluorescence Spectrometry (CVAFS).  Total Particulate Mercury (TPM) concentrations were obtained by collecting airborne particles on micro quartz fibre filters at a flow-rate of 4-.5 lLpm; the mercury collected on the filters was analysed using thermal desorption, followed by gold-trap amalgamation and CVAFS detection. Ambient Typical concentrations of for TGM gaseous mercury measured at the Station were in the range of 0.5-0.9 ng m-3.  During the same period The TPM levels values obtained were between 4.3 and 20 pg m-3. In order to evaluate the effects of different meteorological patterns and the type and location of emission source regions on the levels of mercury in polar regions, the preliminary results of TGM and TPM levels observed in the Antarctica troposphere were compared to those observed in June 1998 in the Arctic at the Zeppelin Station in (Ny-Alesund, on the Svalbard Islands).

 

 

Key Words Index:  mercury, measurements, polar research, Arctic, Antarctic, troposphere

 

 

 

 

IntroductionNTRODUCTION

 

 

 

In the past, remote areas have been considered to be the cleanest locations on Earth unaffected by transport of air pollution, but the Arctic and Antarctic troposphere are part of the global atmospheric circulation and play a fundamental role in global climate; indeed, observations carried out in these areas, particularly in the Arctic, have shown that events, in which gaseous and particulate pollution (Arctic haze layer) alternate with periods in which the air masses are extremely clean according to seasons and meteorological conditions.  Long-range transport studies have shown that atmospheric pollution episodes observed in the Arctic region pollution, in fact, isare related  caused byto the influx of polluted air masses  containing both anthropogenic and natural pollutants from the Northeast of Europe and Eurasia and from North America as well, p, particularly in late winter and spring.  Antarctica, on the contrary, is far from industrialised countries and local anthropogenic pollution sources in general, thus it can probably be considered the cleanest location on Earth where airborne materials of anthropogenic origin are detected at very low concentrations.

 

 

Among heavy metals, mercury plays a distinctive role in environmental pollution due to its rather unique proprieties. The persistent presence of mercury in the atmosphere is due to its low solubility in natural waters and high vapour pressure compared to other metals in their elemental state. Therefore, once introduced into the atmosphere, it can travel for long  distances prior to its transfer to terrestrial and aquatic receptors at remote locations far from its emission sources. Elemental mercury vapour (Hg°) is the most commonly occurring form of mercury in the polar atmosphere. Hg° is relatively unreactive, but gas phase radicals deriving from  photodissociation during polar sunrise, may play a significant role in the notable decrease inof Hg° concentration during this period  in both the Arctic and Antarctic regions.

 

 

 

Mercury associated with the particulate phase represents only a small fraction of the total ambient concentration. This fraction however, plays an important role in determining the deposition fluxes of mercury (Lindberg et al. 1991; Lu et al. 1998; Forlano et al., 2000; Pirrone et al., 2000). 

The aims of this paper are to evaluate the concentrations of gaseous and particulate mercury in the Antarctic troposphere. The data obtained were compared to TGM and TPM concentrations observed sampled in the Arctic during an intensive campaign in June 1998.

 

 

 

 

 

 

ExperimentalXPERIMENTAL

 

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Measurements of Sampling of atmospheric mercury in Antarctica wasere carried out at the CNR-Italian Antarctic Station located in Terranova Bay (74°41’42” South, 164°07’23” East), from November the 5th to 22th 1999.

TGM samples were taken every 24 hours using the manual Au-trap method based on Augold-trap amalgamation at a flow rate of 0.3 Lpm. The Au-traps consisted of a 12 cm quartz tube filled with Au-coated quartz sand.  The sampling system consisted of a tTeflon tube, a Au-trap, a gas meter and a pump. During sample analysis, the sample Au-trap, is first heated externally at 500°C using Ni-Cr alloy resistance heating ribbon. All tThe Hg° released is carried by a stream of Ar and pre-concentrated on the analyityical gold trap, then thermally desorbed at 500°C and detected by a CV-AFS (Fitzgerald and Gill, 1979). 

 

TPM concentrations were obtained by collecting airborne particles on micro-quartz filters mounted in a quartz tube for 48h at a flow-rate of 4-5 l/Lpmmin; the mercury collected on the filters was then released thermally and analysed by gold-trap amalgamation and CV-AFS detection. In order to reduce the blanks, all TGM and TPM traps were cleaned by heating them repeatedly before the sampling.

 

 

 

 

RESULTS AND DISCUSSION

esults and Discussion.

 

The TGM and TPM concentrations in air samples collected at Terranova Bay are shown in Figures 1 and 2.  Ambient concentrations of TGM and TPM are between 0.5-0.9 ng/ m-3 and 4.3-20 pg/ m-3, respectively. Ambient concentrations of TPM show display an general  increase over the sampling period.  The TGM and TPM concentrations  in the two graphs both show distinctive temporal patterns,, specifically the behaviour of the TGM and TPM concentrations appear to show an opposite trends over the sampling period: a general decrease in the amount of Hg° as time progressed, is associated with an increase in TPM concentrations over the same period. The behaviour of TGM, which is primarily comprised mostly of Hg°, may be associated with a number of reactive chemicals reactions that take place in the atmosphere after polar sunrise. The chemistry of the atmosphere in the polar regions areas is different to that of other remote areas of the Earth, primarily due to significant differences in wind flow patterns and therefore pollutant transport as well as , solar irradiation, both of which areof fundamental importance in photochemistry;.  tTherefore, these and other factors may cause changes in the chemical reactions that take place and may influence the general trend of atmospheric air pollutants such as mercury. 

 

 

During the polar winter months, there is a total lack of solar radiation, the temperature and relative humidity are very low and the vertical mixing of the lower stratified aAntarctic troposphere is hindered. The direct consequence is that the abundance of photochemically labile compounds will rise, while the level of photochemical products will be zero. 

During polar dawn, solar radiation is present again and the elevate concentrations of photodissociable precursor compounds present in the Aantarctic atmosphere may start a sequence of atmospheric chemical transformations often different than that observed at other latitudes.   

 

 

The Antarctic region is surrounded by the Southern Pacific ocean and under higher temperature conditions, many substances derived from sea spray and marine biogenic activity could influence the chemistry of atmospheric mercury in this region; Ttherefore, one possibility is that the TGM trend observed in Antarctica in November, may be associated with photochemical reactions in the boundary layer, that produce elevated concentrations of halogen containing radicals.   The mercury compounds produced by reactions with such radicals may bind to particles which may be deposited to terrestrial receptors. Indeed, the elevated values of TPM concentrations  in Antarctica shown in fFigure 2,  may arise from springtime conversion of atmospheric mercury from gas phase to particulate phase by tropospheric chemical reactions analogous to those resulting in ground-level ozone depletion during springtime in the Arctic. (Schroeder et al., 1998). 

 

 

 

Frequent episodic depletions in mercury vapour concentrations were observed in the Arctic (Alert, Canada) during the three -month period following polar sunrise (from April to early June) by Schroeder et al. (1998) during 1995.  The observed mercury depletion recorded strongly resembled depletions of ozone occurring in the same period, souggesting that the decrease in TGM levels during springtime in TGM may be linked to the  tropospheric ozone depletion seen in the Arctic (Schroeder et al. 1998). Therefore, it is possible that the behaviour of TGM in the Antarctic troposphere may be in part explained in light of seasonal ambient conditions during the measurement period.

 

 

 


 

 


Figure 1 - Ambient concentrations (ng m-3) of Total Gaseous Mercury (TGM) observed at Terranova Bay in Antarctica in November 1999

 

The TGM and TPM levels observed recorded in Antarctica are compared with that other preliminar results obtained during a measurement campaignobserved during an intensive field campaign carried out in June, 1998 in the Arctic in (Ny-Alesund, on the Svalbard Islands) (Sprovieri and Pirrone, 2000). 

The TGM values obtained in theNy-Alesund Arctic  are higher than thoseat observed recorded at Terranova Bay. This may be due to the different chemical composition of the troposphere as a result of a different topography and geographical configuration of the continents and oceans relative to the measurement locations in the two regions, (Barrie et al., 1995).

 The Arctic, in fact, is surrounded by populated continents from which atmospheric pollutants areion is released and transported to the north; the Antarctic, in contrast, is entirely surrounded by the Pacific Ocean and is far from any anthrophogenic emissions, thereforeso the tropospheric concentration of many gases is much higher in the Arctic than in the Antarctic. In particular, fluxes of mercury to the atmosphere, primarily mainly from anthropogenic and continental sources in the Northern Hemisphere (particularly from Eurasia and North America in late winter and spring), are greater than those in the Southern Hemisphere, and higher atmospheric Hg concentrations are found in Arcticthe nNorthern hHemisphere  are higher than theat observed in the  Ssouthern Hemisphere Antarctica.

 

 


 


Figure 1 –   Ambient concentrations (ng m-3) of Total Gaseous Mercury (TGM) observed at Terranova Bay in Antarctica in November 1999

 

Figure 2 –   Ambient concentrations (pg m-3) of Total Particulate Mercury (TPM) observed at Terranova Bay in Antarctica in November 1999.

 

(Fitzgerald, 1986).

 

TPM concentrations in the Arctic were between 2 and 5 pg m-3 which is in agreement with that (1.2-5.2 pg m-3) observed at the same location by Lu et al. (1998).  In contrast, TPM levels in Antarctica are generally higher than those observed in the Arctic, this is probably due to a significant difference in the altitude of sampling stations, (~500 m a.s.l. in the Arctic and ~90 m a.s.l. in Antarctica), different meteorological patterns as well as magnitude and the location of natural and anthropogenic emission sources in the regions. 

 

 

 

 

Figure 1 – Ambient concentrations (ng m-3) of Total Gaseous Mercury (TGM) observed at Terranova Bay in Antarctica in November 1999.

 

 

 

Figure 2 – Ambient concentrations (pg m-3) of Total Particulate Mercury (TPM) observed at Terranova Bay in Antarctica during November 1999.

 

 

Final RemarksINAL REMARKS

 

 

Our preliminary results obtained during a short measurement campaign, can not fully explain the  chemical transformations of mercury and its interactions with other chemical species (i.e., O3, halogens) that could take place in the Antarctic troposphere.,  However, it can be anticipated that in the polar troposphere, free radical precursors that build up in the darkness of the polar winter begin to photodissociate and the resulting gas phase radicals may play a fundamental role in the elemental gas phase mercury decrease observed in Antarctica.  tTherefore, in order to improve our understanding of all those processes/mechanisms affecting chemical and physical transformations and spatial distributions of mercury in polar regions the atmospheric measurement program other experiments will be carried out inat Terranova Bay in Antarctica  Antarctica will continue for the next for the next two years and will be integrated with chemical speciation of Hg in air and snow samples along with continuous measurements of O3 and halogens.  in order to improve our understanding of all those processes affecting the chemical and physical transformations and spatial distributions of mercury in polar regions.  

 

 

Yet it can be anticipated that in the polar troposphere, free radical precursors that build up in the darkness of the polar winter begin to photodissociate and the resulting gas phase radicals may play a fundamental role in the elemental gas phase mercury decrease observed in Antarctica.

 

 

 

AcCkKnNoOwWlLeEdDgGeEMENTSments

This project is part of the PNRA and the financial support received from ENEA is greatly acknowledged. The authors are grateful to Mr. Montagnoli of the CNR-IIA for his assistance during the field measurements.

 

 

 

 

 

 

REFERENCES

 

 

Barrie et al., 1995 ………..

LLu J.Y., Schroeder W.H., Berg T., Munthe J., Schneeberger D. and Schaedlich F. (1998) A Device for

       Sampling and Determination of Total Particulate Mercury in Ambient Air.  Anal. Chem. 70,: 2403-2408.

Fitzgerald W.F. and G.A. Gill (1979) Sub nanogram determination of mercury by two-stage Au amalgamation in gas phase detection applied to atmospheric analysis.  Anal. Chem. 51:, 1714-1720.

Forlano, L., Hedgecock, I., Pirrone, N. (2000) Deposition and Speciation of Atmospheric Mercury as it Interacts with the Ambient Aerosol.  Science of the Total Environment (In press).

Pirrone, N., Hedgecock, I., Forlano, L. (2000) The Role of the Ambient Aerosol in the Atmospheric Processing of Semi-Volatile Contaminants: A Parameterised Numerical Model (GASPAR). Journal of Geophysical Research 105, D8, 9773-9790  Journal of Geophysical Research (In press).

Lindberg et al. 1991 ……….

Schroeder W.H., Anlauf K.G., Barrie L.A., Lu J.Y., Steffen A., Schneeberger D.R., Berg T. (1998) Arctic springtime depletion of mercury. Nature 394:, 331-332.

Sprovieri, F. and Pirrone, N. (2000) A Preliminary Assessment of Mercury Levels in the Antarctic and Arctic Troposphere. Journal of Aerosol Science (In press).

 

 

 

 

 

 

 

 

 

Figure 2 – Ambient concentrations of Total Particulate Mercury (TPM) observed at Terranova Bay in Antarctica during November 1999.
 
 


Figure 2 – Ambient concentrations (pg m-3) of Total Particulate Mercury (TPM) observed at Terranova Bay in Antarctica during November 1999.
 

Figure 2 – Ambient concentrations (pg m-3) of Total Particulate Mercury (TPM) observed at Terranova Bay in Antarctica during November 1999.
 
Sprovieri, F. and Pirrone, N. (2000) A Preliminary Assessment of Mercury Levels in the Antarctic and Arctic Troposphere. Journal of Aerosol Science (In press).