Apartįrom aircraft campaigns, mountain observatories are currently the only However, such observations are rare, especially in the SH. Troposphere are less sensitive to direct surface–atmosphere interactions than in the boundary layer, it could be argued that Hg observations in theįree troposphere are especially valuable for constraining Hg redoxĬhemistry. Insufficiently constrained by observations. Introducing, among others, a two-step OH-initiated oxidation pathwayĪlongside the abovementioned Br-induced pathway and by introducing O 3 as a second-stage oxidant for both the Br- and OH-initiated oxidation pathways.ĭespite these important new developments, Hg redox chemistry remains Updated by Shah et al. (2021), who somewhat reconciled earlier studies by In recent versions a two-step Br-initiated pathway as the main Hg 0Įt al., 2017 Feinberg et al., 2022).
Indeed, the widely used mercury simulation of the GEOS-Chem chemical transport model (Selin et al., 2007) employed (Schroeder et al., 1998) led to the increasingĬonsideration of halogens, mainly bromine (Br) radicals, as important Hg Besides, the detection of Hg 0 depletion events in polar regions (Calvert and Lindberg, 2005 Dibble et al.,Ģ020). Or OH is likely insignificant in the real atmosphere Homogeneous and direct oxidation of Hg 0 to Hg II via either O 3 However, thermodynamicĬonsiderations and quantum chemistry calculations showed that the Was assumed that atmospheric ozone (O 3) and hydroxyl radicals (OH) actĪs dominant Hg oxidants (Lin, 2011). Has been ongoing for more than 2 decades (Lin, 2011 Ariya et al., 2008 Lindberg et al., 2007 Dibble et al., 2020 Ĭalvert and Lindberg, 2005 Lindqvist and Rodhe, 1985). Uncertainties, and the debate on the dominant Hg oxidants in the atmosphere Hg redox chemistry in the atmosphere is still subject to considerable More quickly than poorly soluble elemental mercury (Hg 0) Mercury (Hg II), water-soluble and readily incorporated into waterĭroplets and adsorbed onto particles, is removed from the atmosphere much Transformations (Travnikov, 2011) because divalent oxidized
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The fate of Hg in the free troposphere,ĭetached from direct surface influences, depends strongly on chemical Within the relatively shallow boundary layer but in the free troposphere where winds tend to be strongest and transport tends to be fastest Transport of Hg, which leads to its global distribution, does not occur In this lowermost layer of the atmosphere, HgĬoncentrations are importantly affected by atmosphere–surface interactions such as local emissions and dry deposition. Most Hg observations in either hemisphere are made at ground level and The Northern Hemisphere (NH) than in the Southern Hemisphere (SH) On the one hand, many more sampling sites exist in Might be about twice as high, as weekly–biweekly sampled RM observations are likely diluted by low-RM contributions from the boundary layer and clouds.Ītmospheric mercury (Hg) observations are unequally distributed over the Maïdo RM is 10.6 pg m −3 (SD: 5.9 pg m −3) on average, but RM in the cloud-free LFT Seasonality contrasts with the weak seasonal variation reported for the SH marine boundary layer but is in line with modeling results, highlighting the added value of continuous Hg observations in the LFT. Nighttime observations in particularly dry air masses and find a notable seasonal variation, with LFT GEM being lowest from December to March (mean 0.66 ng m −3 SD: 0.07 ng m −3) and highest from September to
(8–22 ng m −2 h −1), boundary layer influences during the day,Īnd predominant LFT influences at night. Likely driven by the interplay of important GEM photo-reemission from the
GEMĮxhibits a marked diurnal variation characterized by a midday peak (mean:Ġ.95 ng m −3 SD: 0.08 ng m −3) and a nighttime low (mean: 0.78 ng m −3 SD: 0.11 ng m −3). (21.1 ∘ S, 55.5 ∘ E) in the tropical Indian Ocean. Maïdo mountain observatory (2160 m a.s.l.) on remote Réunion Island Mercury (RM integrated over ∼ 6–14 d) for 9 months at To fill this gap, weĬontinuously measured gaseous elemental mercury (GEM hourly) and reactive Observatories are rare, especially in the Southern Hemisphere (SH), andĪtmospheric Hg in the SH LFT is unconstrained. Sampling of LFT air, inaccessible to most ground-based stations, can beĪchieved at high-altitude observatories. Hg background concentrations on a regional level. Atmospheric mercury (Hg) observations in the lower free troposphere (LFT)Ĭan give important insights into Hg redox chemistry and can help constrain
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