Multiscale Temporal Variations of Atmospheric Mercury Distinguished by the Hilbert–Huang Transform Analysis Reveals Multiple El Niño–Southern Oscillation Links

Abstract

Atmospheric mercury (Hg) cycling is sensitive to climate-driven changes, but links with various teleconnections remain unestablished. Here, we revealed the El Niño–Southern Oscillation (ENSO) influence on gaseous elemental mercury (GEM) concentrations recorded at a background station in East Asia using the Hilbert–Huang transform (HHT). The timing and magnitude of GEM intrinsic variations were clearly distinguished by ensemble empirical mode decomposition (EEMD), revealing the amplitude of the GEM concentration interannual variability (IAV) is greater than that for diurnal and seasonal variability. We show that changes in the annual cycle of GEM were modulated by significant IAVs at time scales of 2–7 years, highlighted by a robust GEM IAV-ENSO relationship of the associated intrinsic mode functions. With confirmation that ENSO modulates the GEM annual cycle, we then found that weaker GEM annual cycles may have resulted from El Niño-accelerated Hg evasion from the ocean. Furthermore, the relationship between ENSO and GEM is sensitive to extreme events (i.e., 2015–2016 El Niño), resulting in perturbation of the long-term trend and atmospheric Hg cycling. Future climate change will likely increase the number of extreme El Niño events and, hence, could alter atmospheric Hg cycling and influence the effectiveness evaluation of the Minamata Convention on Mercury.

Seven-Year Monitoring of Mercury in Wet Precipitation and Atmosphere at the Amsterdam Island GMOS Station

“…S7). This result is in agreement with the findings at Cape Point (South Africa) and Mace Head (Ireland) [67], therefore supporting the influence of El Niño on GEM variability, which can occur with the increased wildfire frequency (which also impacts CO concentration) [67] or with enhanced Hg re-emission from the ocean surface caused by the increase of the sea surface temperature [69,70]. Huang and Zhang indeed recently simulated by GEOS-Chem model a positive anomaly of atmospheric Hg concentration, lagged of 3 months, driven by Hg(0) evasion fluxes after the occurrence of El Niño [71].…”

Measurement report: Atmospheric mercury in a coastal city of Southeast China – inter-annual variations and influencing factors

“…In general, the GEM concentration peaked in the early morning, decreased to a valley in the afternoon, and then rose during the night. The diurnal pattern of GEM concentrations in January 2015 was more gentle than the same period in other years, which might be related to the enhanced effect of air mass transport (Fu et al, 2012;Nguyen et al, 2022). The diurnal pattern of GEM concentrations in Xiamen is consistent with other urban sites like Guiyang, Hefei, and Guangzhou (Feng et al, 2004;Chen et al, 2013;Fu et al, 2015).…”

“…S2). In addition, an adverse effect of meteorological conditions due to an extreme 2015-2016 El Niño event might also have resulted in an increase of GEM concentrations in 2015 (Nguyen et al, 2022).…”

Mercury in the free troposphere and bidirectional atmosphere–vegetation exchanges – insights from Maïdo mountain observatory in the Southern Hemisphere tropics

“…While these observatories are still subject to surface influences and often exhibit a complex variability in the origin of sampled air masses due to orographic and thermal flows (Forrer et al, 2000), they are usually able to sample air from the lower free troposphere (LFT) with regularity, especially during stable atmospheric conditions and at night (Reidmiller et al, 2010;Kleissl et al, 2007;Hahn et al, 1992;Baray et al, 2013;Collaud Coen et al, 2011). Atmospheric Hg observations from NH mountain sites such as Pic du Midi in France (Fu et al, 2016a, c;Marusczak et al, 2017), Mauna Loa in Hawaii (Carbone et al, 2016;Luippold et al, 2020), Jungfraujoch in Switzerland (Denzler et al, 2017), Mount Bachelor (Weisspenzias et al, 2007;Swartzendruber et al, 2006) in the US, Storm Peak (Obrist et al, 2008;Faïn et al, 2009) in the US, and Lulin in Taiwan (Nguyen et al, 2019(Nguyen et al, , 2022Sheu et al, 2010), among others, have provided important insights into the transport and chemistry of atmospheric Hg. Meanwhile, to our best knowledge, mountain-top observations of atmospheric Hg in the SH have until now only been reported from the Chacaltaya observatory in the tropical Bolivian Andes (Koenig et al, 2021).…”