TOTAL GASEOUS MERCURY (T.G.M.) IN CHAMP/DRAC, France FROM JANUARY 12, 2000 TO JANUARY 24, 2000. CORRELATION WITH OTHER POLLUTANT LEVELS AND METEOROLOGICAL PARAMETERS.

Christophe Ferrari^1,2,*, Aurélien Dommergue¹, Audrey Veysseyre¹, Frédéric Planchon¹ and Claude Boutron^1,3

¹ Laboratoire de Glaciologie et Géophysique de l’environnement du CNRS, 54 rue Molière, B. P. 96, 38402 Saint Martin d’Hères, France.

² Institut des Sciences et Techniques de Grenoble, Université Joseph Fourrier de Grenoble, 28 Avenue Benoît Frachon, B.P. 53, 38041 Grenoble , France.

³ Unités de Formation et de Recherche de Mécanique et de Physique, Université Joseph Fourrier de Grenoble (Institut Universitaire de France), B.P. 68, 38041 Grenoble, France.

* corresponding author: ferrari@glaciog.ujf-grenoble.fr

Summary:

This paper deals with the results of a T.G.M. monitoring campaign in Champ sur Drac, France from January 12, 2000 to January 24, 2000. T.G.M. levels are recorded every 10 minutes while ozone, NO, NO₂,SO₂ and meteorological parameters are recorded every 15 minutes. The T.G.M. average concentration is ~3.1 ng/m³ with peaks reaching up to 30 ng/m³. These peaks are correlated with SO₂ levels indicating that the chlor-alkali plant and other industrial local sources located at ~1 km are a major sink of atmospheric Hg.

Introduction:

Mercury (Hg) is released into the atmosphere from various natural (Mason et al., 1994; Lindberg et al., 1995) and anthropogenic sources (Pironne et al., 1996; Carpi and Lindberg, 1997; Lacerda, 1997). Natural sources include earth crust erosion, volcanoes, forests, lakes and oceans (Mason et al., 1994). Anthropogenic sources such as combustion from fossil fuels, waste incinerators, chlor-alkali plants may contribute up to 5000 t/year (Porcella et al., 1997).

Atmospheric Hg can be involved in various physical and chemical transformations in the atmosphere before being deposited. Hg in the atmosphere is mainly on its Hg(0) form. Atmospheric methylated Hg has also been found (< 3% of Total Gaseous Mercury (T.G.M.), Saint-louis et al., 1995). In the atmosphere T.G.M. concentration is in the range 1-4 ng/m³ (Mason and Fitzgerald, 1990). In this paper are presented the results of a T.G.M. monitoring campaign in Champ sur Drac, France from January 12, 2000 to January 24, 2000. T.G.M. levels are compared to those measured for ozone, NO, NO₂ and SO₂. Meteorological parameters such as wind speed, wind direction, temperature, atmospheric pressure, solar irradiation and precipitation intensity are also discussed in order to explain T.G.M. peaks which can be 50 times higher than background.

Material and methods

Total Gaseous Mercury (T.G.M.) has been measured in Champ sur Drac, France from January 12, 2000 to January 24, 2000. Champ sur Drac is located in South-East of France (45,08°N, 5,73 °E) at an elevation of 267 m above sea level. Champ sur Drac is a residential city located near (~1 km) an important chlor-alkali plant (Elf Atochem) using Hg cathod system.

T.G.M. is measured every 10 minutes using a GARDIS 1A+ Hg analyser (Ekoservis, Lituania). 10 liters air are analysed and Hg is collected on two gold traps after having been filtered (Teflon filter, 0.5 µm). T.G.M. is detected using Cold Vapor Atomic Absorption Spectroscopy (C.V.A.A.S.) and data are stored automatically. Other pollutants are also analysed every 15 minutes as for example ozone, NO, NO₂ and SO₂. Meteorological parameters as wind speed, wind direction, solar irradiation, temperature, atmospheric pressure, rain intensity are also recorded every 15 minutes.

RESULTS AND DISCUSSION

1-Character of the data

All the data are given in figure 1. The T.G.M. average concentration is ~3.1 ng/m³ with peaks reaching up to 30 ng/m³. After january 19, 2000 background levels are low reaching the analyser detection limit (below 1 ng/m³). This period from january 12 to january 24 can be divided in three parts:

- From January 12 to January 18, wind speed was low (< 1m/s) giving importance to Hg local sources.

- From January 18 to January 22, wind speed increased up to ~4 m/s with air masses coming from the North.

- From January 23 to January 24, a snow event occured.

2-Hypothesis on Hg sources

- From January 12 to January 18 before mid-day:

We can observe a similar trend between T.G.M. and SO₂ concentrations. This is especially true for the events 1, 2 and 4 (see figure 1) where the concentration peaks are starting at 6:00 am and finishing near 6:00 pm with a maximum near mid-day. This could be the result of local industries. When looking to solar irradiation and temperature for these three days, we can observe that T.G.M. concentration seems to follow solar irradiation and temperature increase. This observation can be explained if we consider that frozzen soil can immobilize Hg deposited during the night in atmospheric water and when soil is thawing, Hg can be injected in the atmosphere by volatilization processes. But this phenomenon is not recorded for the days after. The peak 3 is also attributed to local industries such as chlor-alkali plants.

Chlor-alkali power plant is certainly at the origin of peak 5 (>15 ng/m³). It occured after a north windy flush. The wind speed is two weak to carry polluted air masses from Grenoble, city of 450,000 inhabitants located 15 km North-West from Champ sur Drac.

- From January 18 to January 22:

The peak 6 is recorded after a windy event (wind up to 5 m/s) with a peak for SO₂ occuring at the same time. This peak can be explained by the influence of chlor-alkali plant emissions and local sources of SO₂.

- From January 23 to January 24:

This period is characterized by important snow falls. At mid-night (january 23) NO, SO₂ concentrations rapidly decrease as wind speed increases (up to 3 m/s). An important peak of ozone is recorded followed by an important peak of T.G.M. (peak 7, see figure 1). Levels for NO₂ are low but not negligeable. NO₂ can not be formed by the reaction NO + O₃ ® NO₂ +O₂ at that period because the levels for NO are very low. We can estimate that this peak in T.G.M. is the result of polluted air masses coming from Grenoble where an important waste incinerator is working. But we have to take into account that the chlor-alkali plant is located north to the sampling site, and it can contribute to the T.GM. peak. The same explanation can be given to the peaks 8 and 9 but they are of less intensity. Nevertheless, those three peaks are recorded after an important snow event. Could it be possible that these peaks are a contribution of the snow-pack which could degass the Hg trapped during the precipitation and/or during the formation of the snow flakes ? This question is still in suspence as emission of Hg from the snowpack is not well kown.

References

Mason R.P., Fitzgerald W.F., Morel F.M.M. (1994), Geochim. Cosmochim. Acta. 58: 3191-3198.

Lindberg S.E., Kim K.H., Meyers T.P., Owens J.G. (1995) Environ. Sci. and Technol. 29: 126-135.

Pirrone N. Keeler G.J., Nriagu J.O. (1996) Atmos. Env. 30: 2981-2987.

Carpi A. and Lindberg S.E. (1997) Environ. Sci. and Technol. 29: 126-135.

Lacerda L.C. (1997) Water Air and Soil Poll. 97: 209-221.

Porcella D.B., Ramel C., Jernelöv A. (1997) Water Air and Soil Poll. 97: 205-207.

St Louis V.L., Rudd J.W., Kelly C.A., Barrie L.A. (1995) Water Air and Soil Poll. 80: 405-414.

Mason R.P. and Fitzgerald W.F. (1990) Nature 347: 457-459.

Figure Captions

Figure 1: Champ sur Drac measuring campaign for T.G.M. (recorded every 10 minutes) and O₃, SO₂, NO, NO₂, precipitation intensity, atmospheric pressure, solar irradiation, temperature, wind speed, wind direction (recorded every 15 minutes).