Atmospheric mercury concentrations observed at ground-based monitoring sites globally distributed in the framework of the GMOS network

Abstract

Long-term monitoring of data of ambient mercury (Hg) on a global scale to assess its emission, transport, atmospheric chemistry, and deposition processes is vital to understanding the impact of Hg pollution on the environment. The Global Mercury Observation System (GMOS) project was funded by the European Commission (http://www.gmos.eu) and started in November 2010 with the overall goal to develop a coordinated global observing system to monitor Hg on a global scale, including a large network of ground-based monitoring stations, ad hoc periodic oceanographic cruises and measurement flights in the lower and upper troposphere as well as in the lower stratosphere. To date, more than 40 ground-based monitoring sites constitute the global network covering many regions where little to no observational data were available before GMOS. This work presents atmospheric Hg concentrations recorded worldwide in the framework of the GMOS project (2010-2015), analyzing Hg measurement results in terms of temporal trends, seasonality and comparability within the network. Major findings highlighted in this paper include a clear gradient of Hg concentrations between the Northern and Southern hemispheres, confirming that the gradient observed is mostly driven by local and regional sources, which can be anthropogenic, natural or a combination of both.

Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

“…The highest concentrations (1.4-1.8 ng m −3 ) are found inside the PBL with a strong gradient towards the free troposphere (1.1-1.4 ng m −3 ). This gradient seems to be mainly driven by anthropogenic emissions, as it was not observed in regions with low primary emissions (e.g., Mace Head, Ireland) Sprovieri et al, 2016;Weigelt et al, 2015). Finally, in the stratosphere total mercury concentrations are typically below 1 ng m −3 (0.7-1.0 ng m −3 ) (Slemr et al, 2016;Lyman and Jaffe, 2012).…”

“…Inside the PBL, oxidized mercury (OM) (here, OM is defined as the sum of all oxidized forms of mercury including model species GOM, PBM, and any mercury in the aqueous phase) concentrations are very low and mostly between 20 and 100 pg m −3 in Europe and North America, even in source regions with high anthropogenic emissions (e.g., coal-fired power plants) (Xu et al, 2016;2013;Gay et al, 2013;Tørseth et al, 2012;Prestbo and Gay, 2009;Weiss-Penzias et al, 2015). In China, PBM concentrations up to 1000 pg m 3 and GOM concentrations up to 100 pg m 3 have been observed, but no aircraft observations in the PBL and the LFT are available for this region : (Fu et al, 2015Sprovieri et al, 2016). CARIBIC measurements during intercontinental flights indicate that OM concentrations are also usually below 100 pg m −3 in the upper free troposphere (9000-12 000 m) and only occasionally do high OM concentrations occur, which are probably caused by the direct inflow of OM from the stratosphere or the inflow of oxidizing agents which then react with GEM (Lyman and Jaffe, 2012).…”

“…Based on the combination of ground-based observations from the GMOS network (Sprovieri et al, 2016;GMOS, 2016;Weigelt et al, 2013Weigelt et al, , 2015 and ETMEP observations inside the PBL and the lower troposphere , as well as CARIBIC observations in the upper troposphere and the lower stratosphere (Slemr et al, 2016), we were able to obtain comprehensive vertical mercury profiles for Europe from the surface up to 12 000 m. Here, we present two individual profiles (Fig. 2).…”

“…While gaseous elemental mercury (GEM) makes up the vast majority of total atmospheric mercury near the surface (Sprovieri et al, 2016 this issue), recent aircraft-based observations have indicated that there is significant oxidation of mercury occurring in the free troposphere (FT) (Brooks et al, 2014;Lyman and Jaffe, 2012;Jaffe et al, 2014;Gratz et al, 2015;Shah et al, 2016). However, apart from GEM no individual mercury compound has been identified so far and the atmospheric oxidized mercury is an unknown mixture of mercury bound to Br, Cl, OH, O, and NO 2 compounds .…”

“…The aircraft observations were complemented with ground-based observations from the GMOS measurement network (Sprovieri et al, 2016;GMOS, 2016). In particular, we used data from the ground-based stations in Mace Head, Ireland, and Waldhof, Germany, to augment the ET-MEP profiles .…”