Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Howard, Dean; Edwards, Grant C.

doi:10.5194/acp-18-129-2018

Cited by 27 publications

(42 citation statements)

References 72 publications

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“…Micrometeorological Hg flux measurements undertaken in sub-alpine south-eastern Australia (Nimmo Plain) during summer had an average Hg flux of 0.2 ng m -2 h -1 (SD ± 14.5 ng m -2 h -1 ) (Howard and Edwards, 2018), comparable to the summer fluxes observed at Oakdale (0.67 ng m -2 h -1 , SD ± 7.76 ng m -2 h -1 ). Flux chamber measurements at a background site (Pulganbar, north-eastern New South Wales) observed average fluxes of 0.17 ng m -2 h -1 (SD ± 0.09 ng m -2 h -1 ) in both April and June (Edwards and Howard, 2013), whereas Oakdale experienced net deposition during this time.…”

Section: Mercury Fluxesmentioning

confidence: 53%

“…Relative humidity has been suggested as an indicator of Hg deposition occurring via condensation of water onto the surface vegetation, whereby higher humidity indicates more potential for condensation to occur (Fritsche et al, 2008). Howard and Edwards (2018) suggested that nocturnal Hg depletion events were caused by dew formation and fog creating potential sinks of Hg. Spring diel trends exhibit deposition leading up to sunrise which then shift to emission shortly after sunrise (Figure 3).…”

Section: Mercury Flux Variation Across Seasonsmentioning

confidence: 99%

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Seasonal gaseous elemental mercury fluxes at a terrestrial background site in south-eastern Australia

2020

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Terrestrial air-surface exchange of mercury (Hg) forms an important component of the global Hg cycle, with drivers varying across spatial and temporal scales. These drivers include substrate properties, atmospheric chemistry, and meteorological factors. Vegetation uptake represents the dominant pathway of atmospheric Hg deposition to terrestrial surfaces. This study investigated the drivers of net ecosystem exchange of gaseous elemental mercury (Hg 0) across multiple seasons in order to gain an understanding of the influence of vegetation and other environmental parameters on the Hg 0 air-surface exchange. Measurements were made continuously using a micrometeorological aerodynamic flux gradient method at a low-vegetated background site in southeastern Australia, over 14 months. Mean Hg fluxes and atmospheric concentrations across the entire study period were 0.002 ng m-2 h-1 (SD ± 14.23 ng m 2 h-1) and 0.68 ng m-3 (SD ± 0.22 ng m-3), respectively. Variability was observed across seasons, with the highest average rate of emissions occurring in austral summer (December, January, February) (0.69 ng m-2 h-1) and the highest rate of deposition observed in autumn (March, April, May) (-0.50 ng m-2 h-1). Vegetation uptake dominated Hg flux during the winter and spring when meteorological conditions were cold and light levels were low. This is supported by CO 2 flux data, with a daytime winter mean of 0.80 µmol m-2 h-1 and a spring daytime mean of 1.54 µmol m-2 h-1. Summer Hg fluxes were dominantly emission due to higher solar radiation and temperature. Climatic conditions at Oakdale allowed plant production to occur year-round, however the hot dry conditions observed in the warmer months increased evasion, allowing this site to be a small net source of Hg 0 to the atmosphere.

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Section: Mercury Fluxesmentioning

confidence: 53%

Section: Mercury Flux Variation Across Seasonsmentioning

confidence: 99%

Seasonal gaseous elemental mercury fluxes at a terrestrial background site in south-eastern Australia

2020

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“…1). Nam Co Station was established in 2005 to maintain a long-term record of the meteorological, ecological and atmospheric measurements on the Tibetan Plateau (Cong et al, 2007;Li et al, 2007;Kang et al, 2011;Huang et al, 2012;Liu et al, 2015;de Foy et al, 2016b). There are restricted point sources of anthropogenic mercury emissions near Nam Co Station.…”

Section: Measurement Sitementioning

confidence: 99%

“…Further, it has been increasingly perceived that the inland Tibetan Plateau can be influenced by transboundary air pollution such as black carbon originating from biomass burning in South Asia, which crosses the Himalayas (Xia et al, 2011;Cong et al, 2015;Wan et al, 2015;Li et al, 2016). Studies of mercury in precipitation and water vapor evidenced that the Tibetan Plateau is likely sensitive to pollutant input including mercury (Huang et al, 2012(Huang et al, , 2013. Furthermore, the particulate-bound mercury in total suspended particulates was found at high concentrations in Lhasa with an average of 224 pg m −3 , which was comparable to other cities in China (Huang et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Multi-year monitoring of atmospheric total gaseous mercury at a remote high-altitude site (Nam Co, 4730 m a.s.l.) in the inland Tibetan Plateau region

et al. 2018

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Abstract. Total gaseous mercury (TGM) concentrations were continuously measured at Nam Co Station, a remote high-altitude site (4730 m a.s.l.), on the inland Tibetan Plateau, China, from January 2012 to October 2014 using a Tekran 2537B instrument. The mean concentration of TGM during the entire monitoring period was 1.33±0.24 ng m−3 (mean ± standard deviation), ranking it as the lowest value among all continuous TGM measurements reported in China; it was also lower than most of sites in the Northern Hemisphere. This indicated the pristine atmospheric environment on the inland Tibetan Plateau. Long-term TGM at the Nam Co Station exhibited a slight decrease especially for summer seasons. The seasonal variation of TGM was characterized by higher concentrations during warm seasons and lower concentrations during cold seasons, decreasing in the following order: summer (1.50±0.20 ng m−3) > spring (1.28±0.20 ng m−3) > autumn (1.22±0.17 ng m−3) > winter (1.14±0.18 ng m−3). Diurnal variations of TGM exhibited uniform patterns in different seasons: the daily maximum was reached in the morning (around 2–4 h after sunrise), followed by a decrease until sunset and a subsequent buildup at night, especially in the summer and the spring. Regional surface reemission and vertical mixing were two major contributors to the temporal variations of TGM while long-range transported atmospheric mercury promoted elevated TGM during warm seasons. Results of multiple linear regression (MLR) revealed that humidity and temperature were the principal covariates of TGM. Potential source contribution function (PSCF) and FLEXible PARTicle dispersion model (WRF-FLEXPART) results indicated that the likely high potential source regions of TGM to Nam Co were central and eastern areas of the Indo-Gangetic Plain (IGP) during the measurement period with high biomass burning and anthropogenic emissions. The seasonality of TGM at Nam Co was in phase with the Indian monsoon index, implying the Indian summer monsoon as an important driver for the transboundary transport of air pollution onto the inland Tibetan Plateau. Our results provided an atmospheric mercury baseline on the remote inland Tibetan Plateau and serve as new constraint for the assessment of Asian mercury emission and pollution.

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“…Photo-reduction is a major driver of TGM evasion from the Earth's surface (Howard and Edwards, 2018;Kuss et al, 2018;Gao et al, 2020), and this is due to photochemically mediated reduction that converts soil Hg 2+ to volatile Hg 0 and enhances the Hg 0 pool in the soil pore (Xin and Gustin, 2007;Choi and Holsen, 2009a). Therefore, the elevated soil pore Hg 0 concentrations increased the potential of soil pore TGM diffusion to the atmosphere, which drives an increase of Hg emissions from soil.…”

Section: Correlations Between Environmental Factors and Fluxesmentioning

confidence: 99%

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

Zhou¹,

Wang²,

Zhang³

et al. 2020

Preprint

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Abstract. Evasion from soil is the largest source of mercury (Hg) to the atmosphere in terrestrial ecosystems. To improve understanding of controls and reduce uncertainty in estimates of forest soil-atmosphere exchange, soil-air total gaseous Hg (TGM) fluxes were measured for 130 and 96 days for each of four plots at a subtropical forest and a temperate forest, respectively. The soil-air TGM fluxes, measured using dynamic flux chambers (DFC), showed patterns of both emission and deposition at five study plots, with an area-weighted net emission rate of 3.2 and 0.32 ng m−2 hr−1 for the entire subtropical and temperate forests, respectively. At the subtropical forest, the highest fluxes and net soil Hg emission were observed for an open field, with lesser emission rates in coniferous (Masson pine) and broad-leaved (camphor) forests, and net deposition in a wetland. At the temperate forest, the highest fluxes and net soil Hg emission were observed for a wetland and an open field, with lesser emission rates in deciduous broad-leaved and deciduous needle-leaf (larch) forests, and net deposition in an evergreen pine forest (Chinese pine). High solar radiation and temperature in summer resulted in the high Hg emission at the subtropical forest, and open field and evergreen pine forest in the temperate forest. In the temperate deciduous plots, the highest Hg emission was in spring during leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature, and negative correlations with ambient-air TGM concentration in both subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The compensation points implicated that the atmospheric TGM concentration plays a critical role in inhibiting the TGM emission from forest floor. More attention should pay to the legacy Hg stored in terrestrial surface as a more important increasing Hg emission source with the decreasing air TGM concentration recently.

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Mercury fluxes over an Australian alpine grassland and observation of nocturnal atmospheric mercury depletion events

Cited by 27 publications

References 72 publications

Seasonal gaseous elemental mercury fluxes at a terrestrial background site in south-eastern Australia

Seasonal gaseous elemental mercury fluxes at a terrestrial background site in south-eastern Australia

Multi-year monitoring of atmospheric total gaseous mercury at a remote high-altitude site (Nam Co, 4730 m a.s.l.) in the inland Tibetan Plateau region

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

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