Variability in gaseous elemental mercury at Villum Research Station, Station Nord, in North Greenland from 1999 to 2017

Abstract

Abstract. Mercury is ubiquitous in the atmosphere, and atmospheric transport is an important source for this element in the Arctic. Measurements of gaseous elemental mercury (GEM) have been carried out at Villum Research Station (Villum) at Station Nord, situated in northern Greenland. The measurements cover the period 1999–2017, with a gap in the data for the period 2003–2008 (for a total of 11 years). The measurements were compared with model results from the Danish Eulerian Hemispheric Model (DEHM) that describes the contribution from direct anthropogenic transport, marine emissions and general background concentration. The percentage of time spent over different surfaces was calculated by back-trajectory analysis, and the reaction kinetics were determined by a comparison with ozone. The GEM measurements were analysed for trends, both seasonal and annual. The only significant trends found were negative ones for the winter and autumn months. Comparison of the measurements to simulations using the Danish Eulerian Hemispheric Model (DEHM) indicated that direct transport of anthropogenic emissions of mercury accounts for between 14 % and 17 % of the measured mercury. Analysis of the kinetics of the observed atmospheric mercury depletion events (AMDEs) confirms the results of a previous study at Villum of the competing reactions of GEM and ozone with Br, which suggests that the lifetime of GEM is about a month. However, a GEM lifetime of 12 months gave the best agreement between the model and measurements. The chemical lifetime is shorter, and thus, the apparent lifetime appears to be the result of deposition followed by reduction and re-emission; for this reason, the term “relaxation time” is preferred to “lifetime” for GEM. The relaxation time for GEM causes a delay between emission reductions and the effect on actual concentrations. No significant annual trend was found for the measured concentrations of GEM over the measurement period, despite emission reductions. This is interesting, and together with low direct transport of GEM to Villum as found by the DEHM model, it shows that the dynamics of GEM are very complex. Therefore, in the coming years, intensive measurement networks are needed to describe the global distribution of mercury in the environment as the use of models to predict future levels will still be highly uncertain. The situation is increasingly complex due to global changes that most likely will change the transport patterns of mercury, not only in the atmosphere but also between matrixes.

Mercury isotope evidence for Arctic summertime re-emission of mercury from the cryosphere

“…Seasonal air mass provenance was determined using 10-day HYSPLIT back trajectories in a pan-Arctic aerosol study 58 , finding similar lack of origins over Siberian coastal waters for ALT and VRS. A study on long-term Hg 0 observations at VRS used 5-day back trajectories, finding no strong seasonal correlations between Hg 0 and time spent over sea ice, open water, land or snow 26 . The study did not, however, produce seasonal air mass provenance maps for boundary layer air as we present here in Fig.…”

Pan-Arctic surface ozone: modelling vs. measurements

“…The measurements of surface ozone are made by several brands of dual-cell UV absorption monitors, which relate UV absorption to ozone concentration following the Beer-Lambert law. Details can be found in the articles VRS in Skov et al (2004Skov et al ( , 2020 and Alert in Bottenheim et al (2002) or in review articles by e.g. Gaudel et al (2018), Oltmans et al (2010), and Cooper et al (2014).…”

“…The data records of the Canadian sites have recently been re-evaluated (Tarasick et al, 2016). Based on the typical ozone sensor response time of 25-40 s (Smit and Kley, 1998) and assuming a typical balloon ascent rate of 4-5 m s −1 , the ozone-sondes have a vertical resolution of about 100-200 m. Measurement precision is ±3 %-5 %, and the overall uncertainty in ozone VMRs is less than 10 % in the troposphere (Kerr et al, 1994;Smit et al, 2007;Tarasick et al, 2016Tarasick et al, , 2019aTarasick et al, , 2020.…”

Pan-Arctic seasonal cycles and long-term trends of aerosol properties from ten observatories

“…Non-parametric means that no prior assumption of a specific distribution is necessary. The test has been widely applied to environmental data sets including in the Arctic (Tunved and Ström, 2019;Skov et al, 2020;Heslin-Rees et al, 2020;Collaud Coen et al, 2020b, a), not least because of its non-parametric nature and its tolerance of missing values. The null hypothesis of the test is that no trend exists.…”