Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow

Abstract

Abstract. Sunlit snow is highly photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Here, we investigate the behaviour of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in atmospheric new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species and their interaction in surface snow. The mechanisms are still poorly constrained, and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes Three sampling campaigns conducted at an hourly resolution for 3 d each were carried out near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine in surface snow under different sunlight and environmental conditions (24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a different behaviour of mercury and iodine in surface snow during the different campaigns. The day–night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently, bromine did not show any diurnal cycle. The diurnal cycle also disappeared for Hg and iodine during the 24 h sunlight period and during 24 h darkness experiments supporting the idea of the occurrence (absence) of a continuous recycling or exchange at the snow–air interface. These results demonstrate that this surface snow recycling is seasonally dependent, through sunlight. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced atmospheric nucleation processes.

Overview: Integrative and Comprehensive Understanding on Polar Environments (iCUPE) – concept and initial results

“…We carried out an analysis of the monthly, seasonal, and interannual variability in concentration patterns as well as the occurrence of atmospheric Hg de-pletion events (AMDEs) and elevated events (AMEEs). Subsequently, we determined Hg fluxes to the atmosphere, evaluated concentration trends, and identified possible long-range transport cases (with the Hybrid Single-Particle Lagrangian Integrated Trajectory model, HYSPLIT; Stein et al 2015) originating from Icelandic volcanic eruptions (Pankratov et al, 2015).…”

“…Most of the layers were recognized in both approaches, yet the arrival heights of the back trajectories were not always similar to the heights of the layers from HSRL. These discrepancies are due to small-scale vertical motions that are not resolved in the HYSPLIT model (Stein et al, 2015).…”

A 120 000-year record of sea ice in the North Atlantic?

“…To estimate the source of bromine and sodium deposited at Renland, daily back trajectories were calculated from 2000 CE to 2016 CE with HYSPLIT4 (Stein et al, 2015;Draxler et al, 1999;Hess, 1998, 1997), using publicly available NCEP/NCAR Global Reanalysis meteorological data (1948-present), with a 2.5 • resolution in both latitude and longitude (Kalnay et al, 1996). The back trajectories were started daily on an hourly basis at 500 m above the Renland elevation (71.305 • N, 26.723 • W; 2315 m a.s.l.)…”

“…In the Arctic, the most robust piece of evidence results from hourly resolved surface snow measurements carried out in coastal Svalbard, showing that bromine photolytic loss cannot be appreciated across night-day cycles (Spolaor et al, 2019;see Fig. 6).…”

Integrative and comprehensive Understanding on Polar Environments (iCUPE): the concept and initial results

“…To expand the knowledge on the role of snowpack in the Hg life cycle, we performed targeted field studies (Spolaor et al, 2018(Spolaor et al, , 2019 to determine the seasonality of Hg deposition as well the total Hg deposition from the atmosphere to snow preserved in the Arctic environment in the Svalbard archipelago, specifically in the Spitsbergen region (Fig. 12).…”