Gaseous mercury distribution in interstitial air of snow pack in Station Nord, Greenland. Evidence of permanent mercury depletion event in the air of snow during polar sunrise

Gaseous Elemental Mercury (Hg°) concentrations have been measured in Station Nord, Greenland in the air of the snowpack from February 25$^{\rm th}$ to march 15$^{\rm th}$, 2002, during twilight and low solar irradiation periods. The concentration of Hg$^{\circ}$ decreases rapidly with depth in the snow pack air from ~1.5 ng/m$^3$ outside to ~0.1 ng/m$^3$ at 120 cm depth. Adsorption of mercury on snow could not explain such profile since temperature increases with depth (~-13 °C at 120 cm below the surface and ~-35 °C at the surface). Additionally calculations indicate that a poor fraction of Hg° could be adsorbed onto snow. A possible argument to explain such a decrease of Hg° with depth is to investigate homogeneous and/or heterogeneous chemistry occurring at the air/snow interface initiated by sun light. The Arctic snowpack is known to produce active bromine and chlorine species in the frame of interactions between sea-salts, ozone and acid species in the snow. The lifetime of Hg° is calculated on the basis of reactions with various reactive species in the gaseous phase existing in the interstitial air during twilight and under low solar irradiation periods, such as BrCI, Br$_2$, HOBr, Br, BrO and OH. We assume that the decrease of Hg° concentration with depth is the result of the reaction between Hg° and Br and/or BrO, which give a lifetime for Hg°$<$~0.8-8 hours based on known kinetic constants found in the recent literature. This decrease of mercury in the air of the snowpack indicates that during polar sunrise in the Arctic, mercury is probably accumulated in the snowpack on its oxidised form Hg (II), probably HgO. Therefore, the snowpack could be a sink of mercury in trie Arctic in spring where a permanent Mercury Depletion Event (M.D.E.) could exist at polar sunrise

Determination of bismuth down to sub PG/G level in Greenland snow by laser excited atomic fluorescence spectrometry

We present here preliminary data on the first direct determination of Bi in Greenland recent snow down to the sub pg/g level by Laser Excited Atomic Fluorescence (LEAF) spectrometry in clean room conditions. Calibration of the spectrometer was achieved using ultralow concentration Bi standards (concentration range 0.05 - 50 pg/g). The limit of detection was found to be 2.5 fg Bi. Various Greenland samples were analysed, giving Bi concentration values in good agreement with these anticipated from the available volcanic emissions data

Mercury speciation into tropospheric clouds

Cloud water bas been sampled at the Puy De Dôme (France) for mercury determination. The analysis of these samples gave us concentrations from about 10 to 50 ng/L and from about 0.8 to 3.5 ng/L for total mercury (Hg$_{\rm T}$) and for reactive mercury (Hg$_{\rm R}$) respectively. In a previous study based on analysis of Total Gaseous Mercury in the interstitial phase of clouds, mercury concentrations in cloud water were estimated to be around 1 $\mu$g/L. Comparing this assumption with our measurements, we suggest that Hg'could be the principal mercury species in cloud water. A kinetic study, which compares reduction and oxidation processes, supports our hypothesis. Assuming our assumption to be tme, precipitation is likely to contribute significantly to elemental mercury deposition

Present century record of mercury species pollution in high altitude alpine snow and ice

Mercury speciation analysis has been performed in an ice/snow core drilled at an altitude of 4250 m in the Col du Dôme glacier on the Mont Blanc, France. The study provides the first time series for mercury speciation analysis in the Alpine snow/ice for the last century. Measured concentrations range from 0.25 to 3.96 pg g$^{-1}$ for MeHg$^+$ and 0.20 to 1.80 pg g$^{-1}$ for Hg$^{2+}$. Since the beginning of 20$^{\rm th}$ century, a clear increase in total mercury concentration is observed with a maximum for 1965 with an approximately 5-fold increase compared to 1885. A drop in both methylmercury and total mercury concentrations was observed after 1965 and might be linked with the reduction in the mercury emissions from anthropogenic activities

DIRECT DETERMINATION OF LEAD AND CADMIUM DOWN TO SUB pg/g LEVEL IN ANTARCTIC AND GREENLAND SNOW AND ICE BY LASER ATOMIC FLUORESCENCE SPECTROMETRY

We present here the results of the first direct measurements of Pb and Cd in Antarctic and Greenland ancient ice and recent snow at ultralow concentration levels by Laser Excited Atomic Fluorescence Spectrometry with Electrothermal Atomization (LEAF-ETA) in clean room conditions. The limit of detection was found to be about 5 fg for Pb and 0.5 fg for Cd. Various snow and ice samples were analysed, allowing to reconstruct the past variations of the natural global atmospheric cycles of these two toxic metals during the last climatic cycle and to assess their recent alteration by man in both hemispheres

ln field kinetic experiments to better understand chemical mechanisms involved during mercury depletion events (MDE): Preliminary results

In order to better understand MDE chemistry, which are thought to happen in the presence of halogenated (chloride and bromide) species, we have led several kinetic experiments with gaseous mercury, ozone and chlorine in Teflon bags under polar atmospheric conditions. The chlorine was expected to produce, with natural solar radiation, the reactive chloride species assumed to play a role in the MDE mechanism. The aim of the first experiment was to study the reactivity between ozone and gaseous mercury : we obtained a rate constant of $(13 \pm 6)^*10^{-20}$ cm$^3$molec/s, which is roughly comparable to constants given in the literature. Conceming the second experiment, for which chlorine has been introduced, a rate constant of ($6.2 \pm 2.2))^*10^{-17}$ cm$^3$/molec/s for the reactivity of gaseous mercury was obtained. This constant is too weak to recover the atmospheric lifetime of gaseous mercury during MDE. This difference is in discussion in this paper

Diurnal cycles of interstitial gaseous mercury inside a sub-arctic snow-pack prior to and during snowmelt events

The snowpack is a medium that greatly interacts with a variety of atmospheric gases. Its role in the mercury depletion events in arctic and sub-arctic regions seems to be crucial though it is poorly understood. We studied an environmental component of mercury that is interstitial gaseous mercury (IGM) present in the air of the snowpack at Kuujjuarapik (55°N, 77°W), Québec in April 2002. Our data demonstrate that the snow-pack plays a major role in the global mercury cycle. Indeed. IGM concentrations exhibit a well-marked diurnal cycle with uninterrupted events of Hg° depletion and production within the snowpack. During snowmelt episode, high IGM concentrations ($-20$ ng/cm$^3$ at a depth of 37 cm) have been recorded. This study gives us the confirmation that Hg° is involved in oxidation processes occurring in the snowpack. Additionally, we assume that the impressive production of Hg° during the daytime may be the results of photoreduction and photo-initiated reduction of Hg(II) complexes.

Strontium isotope measurements in Greenland ice from the last glacial maximum to the early Holocene

Strontium isotopic composition and concentration have been measured by thermal ionisation mass spectrometry on a suite of samples from the GRIP ice core drilled at Summit, Greenland. The sample ages range from ~24 to ~7.3 ky BP extending from the last glacial maximum into the early Holocene. Less than 10 g of sample was used for each analysis. No attempt was made to separate soluble/insoluble species in the samples. Sr concentrations are between ~950 and ~1,550 pg.g$^{-1}$ over the period ~24 ky to ~14 ky BP but fall dramatically to generally less than 150 pg.g$^{-1}$ between ~14 to ~7.3 ky BP. The $^{87}$Sr/$^{86}$Sr ratio shows a general rising trend from ~0.712 to ~0.715 over the entire period however there are a number of significant deviations from this trend which are most likely due to changing source regions for aerosol dust input to Greenland. Sr isotopic composition shows a strong correlation with $\delta^{80}$O suggesting that climate plays a strong role in determining regions for dust release

Present century record of mercury species pollution in high altitude alpine snow and ice

Mercury speciation analysis has been performed in an ice/snow core drilled at an altitude of 4250 m in the Col du Dôme glacier on the Mont Blanc, France. The study provides the first time series for mercury speciation analysis in the Alpine snow/ice for the last century. Measured concentrations range from 0.25 to 3.96 pg g$^{-1}$ for MeHg$^+$ and 0.20 to 1.80 pg g$^{-1}$ for Hg$^{2+}$. Since the beginning of 20$^{\rm th}$ century, a clear increase in total mercury concentration is observed with a maximum for 1965 with an approximately 5-fold increase compared to 1885. A drop in both methylmercury and total mercury concentrations was observed after 1965 and might be linked with the reduction in the mercury emissions from anthropogenic activities

One hundred fifty-year record of lead isotopes in Antarctic snow from Coats Land

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period similar to 1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 nu and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Ph concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1,208 for Pb-206/Pb-207 ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Ph reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the similar to1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica