Forurens: Mercury in the Arctic: The roles that atmosphere, aerosols, snow and ground play on the mercury cycle at Ny-Ålesund.

It was discovered in 1995 that, during the spring time, unexpectedly low levels of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). The phenomenon is called Atmospheric Mercury Depletion Events (AMDE) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. This is because studies have indicated the possibility of large depositional fluxes of Hg occurring during AMDEs. While the ecological importance of AMDEs in cold environments is now accepted by the scientific community, several uncertainties remain in our understanding of the AMDE phenomenon. The present project include research efforts that are needed to move the state of knowledge further. WP1: Reactive gaseous mercury shows negative trends for some months whereas particulate Hg is increasing some months. The interaction between aerosol particles and different Hg reservoirs was studied further using size specific correlations. The latest investigations reaffirm that periods with high correlation (both positive or negative) between aerosol properties and Hg, but that different size ranges correlate at different time periods. The exact nature of the controlling processes is not known and further research is needed. However, resent results (Dell,Osto et al 2017) using the aerosol data from the Zeppelin station, indicate a link between particle formation and biogenic processes in the ocean. Since the same biogenetic processes release large amounts of halocarbons that participate in ozone chemistry, there is an interesting prospect that the link between Hg and particles may be via the ocean. At least during late summer and summer when the air reaches Svalbard, there has been a chance to travel over open water. However, this hypothesis must be further tested. WP 2: Quantification of the air exchange of Hg is essential for understanding the Arctic and global Hg cycle. The measurements have ceased and a lot of resources have been spent on quality assurance of data. Maintaining continuous field measurements in the harsh Arctic environment, with ever-changing meteorological conditions, has been extremely challenging. Since we have continuous measurements from many years, we can say something about the overall air exchange and how it changes over time. We observe net deposition in the winter when the ground is covered with snow and is absent. In the spring there is extreme variation associated with dilution episodes, in the spring and little exchange in the summer. During the 9-year measurement period, we see little change in the exchange, except in the autumn, where decreasing emissions are observed. The reason for this is currently unknown but may be related to changed climate. WP 3: UV radiation profiles and meteorological data are believed to be the most important driving factors for mercury deposits. However, a quantitative understanding is insufficient. Non-linear properties are observed. We study the effect of the radiation regime on the formation of reactive gaseous mercury. This includes measurements and reconstruction of relevant UV radiation quantities associated with AMDEs, as well as multivariate statistical analysis and modeling of relationships with the surrounding Hg. The analysis has now been completed and presented in an MSc thesis. WP 4: The Hg levels were studied in humus-rich surface soil and mineral soil from several sampling sites around Ny-Ålesund and Longyearbyen. An average Hg concentration of 0.111 ± 0.036 µg / g in surface soil was obtained. Hg levels in mineral soil were significantly lower than in the corresponding surface soils. Hg accumulates strongly in the surface soil (upper 3 cm) and is associated with SOM (surface soil: 59 ± 14%). The Hg concentrations in surface soil were slightly lower than those in the humus layer on the mainland and were comparable to levels in soil elsewhere in the Arctic. An inverse ratio of Hg was found with elements attributed to the mineral soil, indicating that Hg is mainly derived from atmospheric deposition. Furthermore, Hg and other typical atmospheric deposited metals in the Bayelva river water were studied. Here, differences in concentrations between early spring and summer / autumn were studied based on samples collected over several years. In addition, snow samples were collected in April 2017, and analyzed for elemental composition and organic material (both in filtered and unfiltered molten snow samples). Briefly, a significantly higher concentration of Hg and typical atmospherically deposited elements was observed in the early spring snow melting period.

RGM viser negativ trend for noen måneder, mens partikulært Hg viser positiv trend for noen måneder. ' Det er perioder med høy korrelasjon mellom aerosolegenskaper og Hg, men forskjellige størrelsesområder korrelerer ved forskjellige tidsperioder. Den eksakte naturen til de kontrollerende prosessene er ikke kjent, og videre forskning er nødvendig. Det observeres netto avsetting om vinteren når bakken er dekket med snø. Om våren er det ekstrem variasjon som henger sammen med fortynningingsepisoder og lite utveksling om sommeren. Om høsten observeres det minkende emisjon, som kan skyldes endret klima. Målinger og rekonstruksjon av relevante UV-strålingskvantiteter assosiert med AMDEs har blitt utført. Hg-nivået i overflatejorda var høyere enn i mineraljorda pga atmosfæren som hovedkilde. Nivået var litt lavere enn fastlandet og var sammenlignbare med nivåer i jord på andre steder i Arktis. I Bayelva ble det funnet forskjeller i konsentrasjoner av Hg gjennom sesongen.

It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however cond itions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). The phenomenon is called Atmospheric Mercury Depetion Events (AMDE) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while sti mulating a significant amount of research to understand its impact to this fragile ecosystem.This is because studies have indicated the possibility of large depositional fluxes of Hg occurring during AMDEs. While the ecological importance of AMDEs in cold environments is now accepted by the scientific community, several uncertainties remain in our understanding of the AMDE phenomenon. The present project include research efforts that are needed to move the state of knowledge further: These are: 1) What p article size range is most characteristic for hosting particulate Hg? 2) How is the distribution of Hg on aerosol particles dependent on regional vs local processes? 3) Can we detect a cloud-signal in the particulate distribution of Hg based on air mass h istory? 4)Can we observe systematic similarities/ differences between Hg and other aerosol species such as Black Carbon with respect to the questions above? 5) What is the annual and seasonal variability in the mercury flux? 6) Is the surface (snow and soil) in Ny-Ålesund a sink for mercury? 7) What effect has the radiative regime (solar elevation, clouds, aerosols, surface reflection, etc.) and the associated ultraviolet radiation profiles on the formation of reactive gaseous mercury? 8) What effect h as the complexation capacity and redox properties of dissolved natural organic matter in soil water and rivers?