Mercury distribution in the upper troposphere and lowermost stratosphere according to measurements by the IAGOS-CARIBIC observatory: 2014–2016

Abstract

Abstract. Mercury was measured onboard the IAGOS-CARIBIC passenger aircraft from May 2005 until February 2016 during near monthly sequences of mostly four intercontinental flights from Germany to destinations in North and South America, Africa and South and East Asia. Most of these mercury data were obtained using an internal default signal integration procedure of the Tekran instrument but since April 2014 more precise and accurate data were obtained using post-flight manual integration of the instrument raw signal. In this paper we use the latter data.Increased upper tropospheric total mercury (TM) concentrations due to large scale biomass burning were observed in the upper troposphere (UT) at the equator and southern latitudes during the flights to Latin America and South Africa in boreal autumn (SON) and boreal winter (DJF). TM concentrations in the lowermost stratosphere (LMS) decrease with altitude above the thermal tropopause but the gradient is less steep than reported before. Seasonal variation of the vertical TM distribution in the UT and LMS is similar to that of other trace gases with surface sources and stratospheric sinks. Speciation experiments suggest comparable TM and gaseous elementary mercury (GEM) concentrations at and below the tropopause leaving little space for Hg2+ (TM − GEM) being the dominating component of TM here. In the stratosphere significant GEM concentrations were found to exist up to 4 km altitude above the thermal tropopause. Correlations with N2O as a reference tracer suggest stratospheric lifetimes of 72±37 and 74±27 years for TM and GEM, respectively, comparable to the stratospheric lifetime of COS. This coincidence, combined with pieces of evidence from us and other researchers, corroborates the hypothesis that Hg2+ formed by oxidation in the stratosphere attaches to sulfate particles formed mainly by oxidation of COS and is removed with them from the stratosphere by air mass exchange, gravitational sedimentation and cloud scavenging processes.

Atmospheric mercury in the Southern Hemisphere – Part 2: Source apportionment analysis at Cape Point station, South Africa

“…Mercury occurs in the atmosphere as gaseous oxidized mercury (GOM), particle bond mercury (PBM) and predominantly as gaseous elemental mercury (GEM). Because of its atmospheric lifetime of about 1 year, once emitted into the atmosphere, GEM is transported on hemispheric and global scales (Slemr et al, 2018). Since usage and emissions of Hg are regulated under the UN Minamata Convention on Mercury (UNEP, 2013).…”

4D dispersion of total gaseous mercury derived from a mining source: identification of criteria to assess risks related to high concentrations of atmospheric mercury

“…Results show that processes of Hg deposition and emission are included in a complex cycle with a large number of factors involved, mainly seasonality, vegetation coverage, temperature, solar radiation, relative humidity, diurnal atmospheric turbulence and the presence of Hg oxidants (Zhu et al, 2016). A maximum emission during diurnal hours was described for soils (Zhu et al, 2015), mine materials (Eckley et al, 2011), water (O'Driscoll et al, 2003), sediments (Sizmur et al, 2017) and snow (Maxwell et al, 2013), while forb leaf (Stamenkovic et al, 2008) and growing broad leaf (Fu et al, 2016) reach their minimum emission rates during diurnal hours. These daily cycles of Hg emissions from soils, water or plants contribute to the increase in the atmospheric mercury pool, especially in the lower layers of the troposphere.…”

“…Numerous Hg transfer pathways are involved in this cycle, and these include soil-atmosphere, soil-plant, plant-atmosphere, water-atmosphere and sediment-water, amongst others. These fluxes have been quantified by different approaches, most of which employ dynamic flow chambers, micrometeorological methods and bulk methods (Carpi and Lindberg, 1997;O'Driscoll et al, 2003;Stamenkovic et al, 2008;Eckley et al, 2011;Zhu et al, 2015;Zhu et al, 2016, amongst others). Results show that processes of Hg deposition and emission are included in a complex cycle with a large number of factors involved, mainly seasonality, vegetation coverage, temperature, solar radiation, relative humidity, diurnal atmospheric turbulence and the presence of Hg oxidants (Zhu et al, 2016).…”

“…These daily cycles of Hg emissions from soils, water or plants contribute to the increase in the atmospheric mercury pool, especially in the lower layers of the troposphere. Most of the available information on this topic is on a scale of kilometres at high altitudes in the range 500-11 000 m from background and contaminated locations (Slemr et al, 2018;Weigelt et al, 2016); however, information about TGM dispersion on a scale of metres is scarce. Some information about these distances comes from episodic monitoring by means of lidar techniques, such as those measured in China, where maximum levels at lower altitudes were detected during night-time hours (Guan et al, 2010).…”

Soil-atmosphere exchange flux of total gaseous mercury (TGM) in subtropical and temperate forest catchments

“…Unlike other heavy metals in the atmosphere, the Hg mainly exists as Hg 0 , which accounts more than 90% of total gaseous Hg (TGM). Due to the long longevity, atmospheric Hg 0 is able to undergo over long distances to areas without anthropogenic emissions (Kamp et al, 2018;Slemr et al, 2018). Global long-range atmospheric transport and deposition is the main pathway of Hg input to remote ecosystems (Obrist et al, 2018;Zdanowicz et al, 2018;Motta et al, 2019).…”