Recent findings on the atmospheric cycling of mercury

1. Recent findings on the atmospheric cycling of mercury John MuntheIVL Swedish Environmental Research InstituteGothenburg Sweden john.munthe@ivl.se

2. Topics for this presentation • Field measurements of atmospheric mercury species • Chemistry • Air-sea exchange • Arctic cycling • Policy?

3. Why speciation of atmospheric mercury? • Speciation determines: • Control technology options • Deposition patterns and mechanisms • Atmospheric residence time and transport distance • Health and environmental impact

4. Atmospheric Hg species • TGM (Total Gaseous Mercury) mainly Hg0, atmospheric residence time of 1 yr. Global background increased by a factor of 3 due to anthropogenic emissions • RGM (Reactive Gaseous Mercury) mainly HgCl2, atmospheric residence time of days-weeks. Anthropogenic and atm. formation. • TPM (Total Particulate Mercury). Atmospheric residence time of days-weeks. Anthropogenic and atm. formation. • MeHg(g) Most toxic and bioaccumulating form of Hg. Atmospheric sources unknown.

5. Mace Head (Ireland) Aspvreten (Sweden) Rörvik (Sweden) Zingst (Germany) Neuglobsow (Germany) Calabria (Italy) Mallorca (Spain) Sicily (Italy) Antalya (Turkey) Neve Yam (Israel) MOE measurement sites

6. Wet deposition of Hg in Sweden

7. Main emission sources

8. Average TGM at all MOE stations Distance from main anthropogenic source regions

9. RGM at MOE stations, averages Distance from main anthropogenic source regions

10. MeHg(g) at MOE stations, averages Distance from main anthropogenic source regions

11. TPM at MOE stations, averages Distance from main anthropogenic source regions

12. Field measurements • TGM (Hg0) is mainly global background. Small signal from source areas. Re-emissions from sea influences coastal areas. • RGM (HgCl2) is a dynamic short-lived species. No clear anthropogenic signal, chemistry and deposition processes important

13. Field measurements • MeHg. No link to anthropogenic source areas. Sea surface possible source. Chemistry important? • TPM. Good tracer of anthropogenic emissions but direct emissions are very small. Chemistry (RGM-TPM interactions) and secondary formation is important

14. Speciation - implications for science and policies • Weak relationship between occurrence of TGM, RGM or MeHg, and anthropogenic source areas. • Atmospheric processes need to be well understood to be able to model deposition • TGM is globally distributed in the atmosphere. • Control of European emissions will have limited effect on deposition

15. Gårdfeldt, 2003

16. Chemistry of atmospheric Hg • Important basic information for modelling concentrations and deposition. • Rates of atmospheric oxidation of large pool of Hg0 and reduction of Hg(II) are in steady-state (more or less) with a very small fraction of the Hg0 pool being oxidised and deposited • Number of published scientific investigations with relevant, basic information on reaction kinetic  10 to 20

17. Some recent findings • Previously published mechanism for reduction of Hg(II)(aq) by HO2 proved to be in error (Gårdfeldt and Johnson, 2003) • Significantly affects results of modelled deposition on local/regional scale (if models included previous reduction mechanism)

18. Can new chemistry influence policy? If oxidised Hg (RGM, HgCl2) is emitted from an anthropogenic point source, it can either: - be deposited on local/regional scale, with local/regional impact in ecosystems or - be converted to Hg0, which will add to the global background. Different policy frameworks!!

19. Re-emissions of mercury from water Gårdfeldt et al., 2003

20. Modelled Hg deposition and estimated re-emissions to regional seas Data from Ilyin et al., 2002; Wängberg et al., 2001; Gårdfeldt et al., 2003; Gårdfeldt, 2003

21. What drives the re-emission fluxes? • Availability of volatile Hg (Dissolved Gaseous Mercury, DGM)- Deposition of Hg(II), - Solar irradiation (photoinduced reduction to Hg0)- Biological activity- Natural Sources • Temperature • Wind

22. Relationship between Dissolved Gaseous Mercury (DGM) and flux Gårdfeldt, 2003

23. Re-emissions - implications for science and policy • Re-emissions of Hg from sea surface can be of equal size as wet deposition. • Most current atmospheric models do not take into account re-emissions due to lack of scientifically sound spatially and temporally distributed flux data • Re-emissions from Mediterranean Sea are higher than other marginal seas due to:- Natural sources (tectonic activity)- Higher solar irradiation

24. Hg in the Arctic • Concern for contamination of Arctic ecosystems (marine mammals, human exposure) • No direct sources, impact of global cycling • Mercury Depletion Events discovered in Alert, Canada, by Bill Schroeder, EC.

25. Arctic monitoring sites for Hg

26. Mercury Depletion Events, Alert

27. Mercury Depletion Events • Mechanism for mercury input to Arctic ecosystems? • What are the main chemical and physical mechanisms?

29. O3 BrO TGM TPM RGM Hg, snow

30. Temp TGMchamber

31. Arctic mercury • During depletion events, large amounts of Hg are deposited to snow, ice, and water in the Arctic • A large fraction of the deposited Hg is re-emitted back to the atmosphere • We need measurements, mechanisms and models to estimate the net input • Control strategies need to focus on global scales

32. Final remarks • Ratification of the 1998 protocol on HMs should lead to increased monitoring, emission inventory and basic research activities • The global aspects need to be taken into account (MSC-E hemispherical model)

33. Final remarks • UNEP Governing Council recommends global action to reduce mercury pollution (based on Global Assessment Resport) • EU Council will develop strategy to reduce Hg pollution in 2004. • EU Air Quality Directive. Position Paper on mercury • Cooperation between different policy frameworks is necessary

34. 7:th International Conference on Mercury as a Global PollutantLjubljana, SloveniaJune 27 - July 2, 2004http//:www.cd-cc.si/ICMGP04