scholarly journals Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

2018 ◽  
Vol 18 (1) ◽  
pp. 495-509 ◽  
Author(s):  
Qian Yu ◽  
Yao Luo ◽  
Shuxiao Wang ◽  
Zhiqi Wang ◽  
Jiming Hao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
South China ◽  
Forest Canopy ◽  
Elemental Mercury ◽  
Polluted Site ◽  
Gaseous Elemental Mercury ◽  
Global Emission ◽  
Emission Fluxes ◽  
Flux Measurements

Abstract. Mercury (Hg) exchange between forests and the atmosphere plays an important role in global Hg cycling. The present estimate of global emission of Hg from natural source has large uncertainty, partly due to the lack of chronical and valid field data, particularly for terrestrial surfaces in China, the most important contributor to global atmospheric Hg. In this study, the micrometeorological method (MM) was used to continuously observe gaseous elemental mercury (GEM) fluxes over forest canopy at a mildly polluted site (Qianyanzhou, QYZ) and a moderately polluted site (Huitong, HT, near a large Hg mine) in subtropical south China for a full year from January to December in 2014. The GEM flux measurements over forest canopy in QYZ and HT showed net emission with annual average values of 6.67 and 0.30 ngm-2h-1, respectively. Daily variations of GEM fluxes showed an increasing emission with the increasing air temperature and solar radiation in the daytime to a peak at 13:00, and decreasing emission thereafter, even as a GEM sink or balance at night. High temperature and low air Hg concentration resulted in the high Hg emission in summer. Low temperature in winter and Hg absorption by plant in spring resulted in low Hg emission, or even adsorption in the two seasons. GEM fluxes were positively correlated with air temperature, soil temperature, wind speed, and solar radiation, while it is negatively correlated with air humidity and atmospheric GEM concentration. The lower emission fluxes of GEM at the moderately polluted site (HT) when compared with that in the mildly polluted site (QYZ) may result from a much higher adsorption fluxes at night in spite of a similar or higher emission fluxes during daytime. This shows that the higher atmospheric GEM concentration at HT restricted the forest GEM emission. Great attention should be paid to forests as a crucial increasing Hg emission source with the decreasing atmospheric GEM concentration in polluted areas because of Hg emission abatement in the future.

scholarly journals Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

2017 ◽  
Author(s):  
Qian Yu ◽  
Yao Luo ◽  
Shuxiao Wang ◽  
Zhiqi Wang ◽  
Jiming Hao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
South China ◽  
Forest Canopy ◽  
Elemental Mercury ◽  
Contaminated Site ◽  
Gaseous Elemental Mercury ◽  
Global Emission ◽  
Emission Fluxes ◽  
Flux Measurements

Abstract. Mercury (Hg) exchange between forests and the atmosphere plays an important role in global Hg cycling. The present estimate of global emission of Hg from natural source has large uncertainty partly due to the lack of chronical and valid field data, particularly for terrestrial surfaces in China, the most important contributor to global atmospheric Hg. In this study, micrometeorological method (MM) was used to continuously observe gaseous elemental mercury (GEM) fluxes over forest canopy at a clean site (Qianyanzhou, QYZ) and a contaminated site (Huitong, HT, near a large Hg mine) in subtropical south China for a full year from January to December in 2014. The GEM flux measurements over forest canopy in QYZ and HT showed net emission with annual average values of 6.67 and 1.21 ng m−2 h−1 respectively. Daily variations of GEM fluxes showed an increasing emission with the increasing air temperature and solar radiation in the daytime to a peak at 1:00 pm, and decreasing emission thereafter, even as a GEM sink or balance at night. High temperature and low air Hg concentration resulted in the high Hg emission in summer. Low temperature in winter and Hg absorption by plant in spring resulted in low Hg emission, or even adsorption in the two seasons. GEM fluxes were positively correlated with air temperature, soil temperature, wind speed, and solar radiation while negatively correlated with air humidity and atmospheric GEM concentration. The lower emission fluxes of GEM at the contaminated site (HT) when comparing with that in the clean site (QYZ), may result from a much higher adsorption fluxes at night in spite of a similar or higher emission fluxes during daytime. It testified that the higher atmospheric GEM concentration at HT restricted the forest GEM emission. Great attention should be paid on forest as a critical increasing Hg emission source with the decreasing atmospheric GEM concentration in polluted area because of the Hg emission abatement in the future.

scholarly journals Air/Surface Exchange of Gaseous Elemental Mercury at Different Landscapes in Mississippi, USA

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 538 ◽  
Author(s):  
James Cizdziel ◽  
Yi Jiang ◽  
Divya Nallamothu ◽  
J. Brewer ◽  
Zhiqiang Gao
Keyword(s):  
Forest Floor ◽  
Agricultural Soils ◽  
Elemental Mercury ◽  
Ecological Impacts ◽  
Wetland Soil ◽  
Flux Chamber ◽  
Surface Exchange ◽  
Gaseous Elemental Mercury ◽  
Emission Fluxes ◽  
Mesocosm Experiments

Mercury (Hg) is a global pollutant with human health and ecological impacts. Gas exchange between terrestrial surfaces and the atmosphere is an important route for Hg to enter and exit ecosystems. Here, we used a dynamic flux chamber to measure gaseous elemental Hg (GEM) exchange over different landscapes in Mississippi, including in situ measurements for a wetland (soil and water), forest floor, pond, mowed field and grass-covered lawn, as well as mesocosm experiments for three different agricultural soils. Fluxes were measured during both the summer and winter. Mean ambient levels of GEM ranged between 0.93–1.57 ng m−3. GEM emission fluxes varied diurnally with higher daytime fluxes, driven primarily by solar radiation, and lower and more stable nighttime fluxes, dependent mostly on temperature. GEM fluxes (ng m−2 h−1) were seasonally dependent with net emission during the summer (mean 2.15, range 0.32 to 4.92) and net deposition during the winter (−0.12, range −0.32 to 0.12). Total Hg concentrations in the soil ranged from 17.1 ng g−1 to 127 ng g−1 but were not a good predictor of GEM emissions. GEM flux and soil temperature were correlated over the forest floor, and the corresponding activation energy for Hg emission was ~31 kcal mol−1 using the Arrhenius equation. There were significant differences in GEM fluxes between the habitats with emissions for grass > wetland soil > mowed field > pond > wetland water ≈ forest ≈ agriculture soils. Overall, we demonstrate that these diverse landscapes serve as both sources and sinks for airborne Hg depending on the season and meteorological factors.

Measurements of atmospheric gaseous elemental mercury (GEM) and GEM fluxes in the seas of Southeast Asia in October-December 2019

2020 ◽  
Author(s):  
Viktor Kalinchuk ◽  
Evgeny Lopatnikov ◽  
Anatoly Astakhov ◽  
Maksim Ivanov ◽  
Renat Shakirov ◽  
...  
Keyword(s):  
South China Sea ◽  
Sea Of Japan ◽  
South China ◽  
Elemental Mercury ◽  
Ambient Air ◽  
The South China Sea ◽  
The Sea Of Japan ◽  
The South ◽  
Gaseous Elemental Mercury ◽  
China Sea

<p>Measurements of gaseous elemental mercury (GEM) in the marine boundary layer (MBL) and GEM evasion fluxes were carried out during the Russian-Vietnam cruise conducted from the Sea of Japan to the South China Sea from October 25 to December 7, 2019. All GEM measurements were performed using two RA-915M mercury analysers (Lumex LLC, Russia). Atmospheric GEM concentrations were measured at two levels (about 2 m and 20 m above the sea surface) with a time resolution of 30 minutes. GEM fluxes were measured in the South China Sea using a dynamic flux chamber.</p><p>GEM concentrations ranged between 0.56 ng/m<sup>3</sup> and 25.47 ng/m<sup>3</sup>, and between 0.39 ng/m<sup>3</sup> and 23.95 ng/m<sup>3</sup> with medians of 1.38 ng/m<sup>3</sup> and 1.45 ng/m<sup>3</sup> for 2 m and 20 m measurements, respectively. GEM concentrations were significantly affected by air transport of GEM. Concentration Weighted Trajectory (CWT) analysis showed several source regions potentially influencing GEM concentrations in the ambient air during the cruise: the south of the South China Sea, Vietnam, the southeastern China, the south of Japan and the Korean peninsula. Maximum concentrations (up to 25 ng/m<sup>3</sup>) were registered in Haiphong (Vietnam).</p><p>Hg(0) fluxes measured at 7 stations in the South China Sea ranged from 1.1 ng/m<sup>2</sup>/h to 2.5 ng/m<sup>2</sup>/h, with median value of 2.07 ng/m<sup>2</sup>/h. These values were 1,5 times higher than those that were measured by the same method in the Sea of Japan and the Sea of Okhotsk a month earlier.</p><p>This work was supported by the Russian Science Foundation (RSF) (Project № 19-77-10011).</p>

scholarly journals First eddy covariance flux measurements of gaseous elemental mercury (Hg<sup>0</sup>) over a grassland

2019 ◽  
Author(s):  
Stefan Osterwalder ◽  
Werner Eugster ◽  
Iris Feigenwinter ◽  
Martin Jiskra
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Net Ecosystem Exchange ◽  
Elemental Mercury ◽  
Terrestrial Ecosystems ◽  
Co2 Uptake ◽  
Gaseous Elemental Mercury ◽  
Flux Measurements ◽  
Net Co2 Uptake

Abstract. Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg0) are crucial to improve the understanding of global Hg cycling und ultimately human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg0 flux estimates. Today it remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg0. Here we show a detailed validation of the eddy covariance technique for direct Hg0 flux measurements (Eddy Mercury) based on a Lumex mercury monitor RA-915AM. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m−2 h−1 (maximum) with a 50 % cut-off at 0.074 ng m−2 h−1. The statistical estimate of the Hg0 flux detection limit under real-world outdoor conditions at the site was 5.9 ng m−2 h−1 (50 % cut-off). We present the first successful eddy covariance NEE measurements of Hg0 over a low-Hg level soil (41–75 ng Hg g−1 topsoil [0–10 cm]) in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). We measured a net summertime re-emission over a period of 34 days with a median Hg0 flux of 2.5 ng m−2 h−1 (−0.6 to 7.4 ng m−2 h−1, range between 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m−2 h−1) than nighttime fluxes (1.0 ng m−2 h−1). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation which led to a midday depression in CO2 uptake which did not recover during the afternoon. Thus, the cumulative net CO2 uptake was only 8 % of the net CO2 uptake during the same period in the previous year 2017. We suggest that partial stomata closure dampened Hg0 uptake by vegetation, resulting in a NEE of Hg0 dominated by soil re-emission. Finally, we give suggestions to further improve the precision and handling of the Eddy Mercury system in order to assure its suitability for long-term NEE measurements of Hg0 over natural background surfaces with low soil Hg concentrations (

scholarly journals Eddy covariance flux measurements of gaseous elemental mercury over a grassland

2020 ◽  
Vol 13 (4) ◽  
pp. 2057-2074 ◽  
Author(s):  
Stefan Osterwalder ◽  
Werner Eugster ◽  
Iris Feigenwinter ◽  
Martin Jiskra
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Co2 Flux ◽  
Elemental Mercury ◽  
Terrestrial Ecosystems ◽  
Co2 Uptake ◽  
Global Networks ◽  
Gaseous Elemental Mercury ◽  
Flux Measurements

Abstract. Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg0) are important to improve our understanding of global Hg cycling and, ultimately, human and wildlife Hg exposure. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg0 flux estimates. It currently remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg0. Here, we show a detailed validation of direct Hg0 flux measurements based on the eddy covariance technique (Eddy Mercury) using a Lumex RA-915 AM mercury monitor. The flux detection limit derived from a zero-flux experiment in the laboratory was 0.22 ng m−2 h−1 (maximum) with a 50 % cutoff at 0.074 ng m−2 h−1. We present eddy covariance NEE measurements of Hg0 over a low-Hg soil (41–75 ng Hg g−1 in the topsoil, referring to a depth of 0–10 cm), conducted in summer 2018 at a managed grassland at the Swiss FluxNet site in Chamau, Switzerland (CH-Cha). The statistical estimate of the Hg0 flux detection limit under outdoor conditions at the site was 5.9 ng m−2 h−1 (50 % cutoff). We measured a net summertime emission over a period of 34 d with a median Hg0 flux of 2.5 ng m−2 h−1 (with a −0.6 to 7.4 ng m−2 h−1 range between the 25th and 75th percentiles). We observed a distinct diel cycle with higher median daytime fluxes (8.4 ng m−2 h−1) than nighttime fluxes (1.0 ng m−2 h−1). Drought stress during the measurement campaign in summer 2018 induced partial stomata closure of vegetation. Partial stomata closure led to a midday depression in CO2 uptake, which did not recover during the afternoon. The median CO2 flux was only 24 % of the median CO2 flux measured during the same period in the previous year (2017). We suggest that partial stomata closure also dampened Hg0 uptake by vegetation, resulting in a NEE of Hg0 that was dominated by soil emission. Finally, we provide suggestions to further improve the precision and handling of the “Eddy Mercury” system in order to assure its suitability for long-term NEE measurements of Hg0 over natural background surfaces with low soil Hg concentrations (< 100 ng g−1). With these improvements, Eddy Mercury has the potential to be integrated into global networks of micrometeorological tower sites (FluxNet) and to provide the long-term observations on terrestrial atmosphere Hg0 exchange necessary to validate regional and global mercury models.

Dynamics of gaseous elemental mercury during polar spring and winter

2020 ◽  
Author(s):  
Fidel Pankratov ◽  
Alexander Mahura ◽  
Valentin Popov ◽  
Vladimir Masloboev
Keyword(s):  
Surface Layer ◽  
Solar Activity ◽  
Solar Radiation ◽  
Solar Energy ◽  
Mercury Concentration ◽  
Elemental Mercury ◽  
Ice Cover ◽  
Photochemical Reactions ◽  
High Solar Activity ◽  
Gaseous Elemental Mercury

&lt;p&gt;&lt;strong&gt;Dynamics of gaseous elemental mercury during polar spring and winter&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Since June 2001 the long-term monitoring of the gaseous elemental mercury (thereafter, mercury) in the surface layer of the atmospheric has been conducted near the Amderma settlement (69,72&lt;sup&gt;&amp;#208;&amp;#190;&lt;/sup&gt;N; 61,62&lt;sup&gt;o&lt;/sup&gt;E; Yugor Peninsula, Russia).&lt;/p&gt;&lt;p&gt;During this monitoring, variations of the lowered mercury concentrations (&lt;1.0 ng m&lt;sup&gt;-3&lt;/sup&gt;) were observed for spring (March&amp;#8211;May) period in 2005 and 2011. For spring 2005, the intensity of the solar radiation did not affect the number of low values of mercury concentrations. With an increase of solar activity during the day there was a reverse effect: i.e. from 9 until 15 h the number of lowered values of concentration decreased. For the evening hours, the highest number of lowered concentrations and atmospheric mercury depletion events, AMDEs (12 events) were observed. For 2005, upon reaching a daily high solar activity the processes of mercury depletion were not observed. It could be because lacking of a large number of marine aerosols in the atmospheric surface layer, although the processes of photochemical reactions did not stop. For spring 2011, during increased solar activity the number of AMDEs increased to 62 events. However, there was no ice cover observed in the coastal area, and consequently, large amounts of sea aerosol could be presented in the surface layer of the atmosphere.&lt;/p&gt;&lt;p&gt;For the winter (December-January) period, the maximum number (in total, 495) of lowered values of mercury concentration and AMDEs (32 events) were recorded in 2010&amp;#8211;2011. Such situation was previously observed only in winter of 2006&amp;#8211;2007 (13 events). As there is no direct sunlight in mentioned period, the removal of mercury from the atmosphere may be caused by combination of physical and chemical processes that are not related to photochemistry. Starting mid-January, although duration of the day increases, but solar energy is not enough to activate photochemical reactions and predominant type of solar radiation is diffuse rather than direct one. However, AMDEs were still reported at that time (18 events were registered in January 2011).&lt;/p&gt;&lt;p&gt;After mid-March, the angle of sun&amp;#8217;s declination increases and the incoming solar energy is sufficient to activate photochemistry. However, during March&amp;#8211;May there was no linear relationship identified for AMDEs. The maximum number (300) of lowered values of mercury concentration and AMDEs (21 events, with duration up to 66 hours) were registered in April. Such AMDEs are connected with presence of elevated concentrations of aerosols in the absence of ice cover in the marine coastal zone. Not excluded a possibility of contribution of anthropogenic aerosols (from burning of fossil fuels) in the process of mercury deposition from the atmosphere on the underlying surface.&lt;/p&gt;

Assessing the atmosphere-surface exchange of gaseous elemental mercury using passive air samplers

2020 ◽  
Author(s):  
Meng Si ◽  
Michelle Feigis ◽  
Isabel Quant ◽  
Shreya Mistry ◽  
Melanie Snow ◽  
...  
Keyword(s):  
Time Scales ◽  
Forest Canopy ◽  
Elemental Mercury ◽  
Permafrost Degradation ◽  
Concentration Gradients ◽  
Surface Exchange ◽  
Gaseous Elemental Mercury ◽  
The Earth ◽  
Long Time ◽  
The Impact

&lt;p&gt;The specific properties of gaseous elemental mercury (GEM) allow it to undergo bidirectional exchange between the atmosphere and the Earth&amp;#8217;s surface. Determining the direction and the magnitude of GEM&amp;#8217;s atmosphere-surface flux is possible and has been accomplished using micrometeorological and chamber techniques, but (i) is complex and labor-intensive, and (ii) often only yields fluxes over relatively short time scales. A recently developed passive air sampler for GEM has the precision required for identifying and quantifying vertical concentration gradients above the Earth&amp;#8217;s surface. The feasibility and performance of this approach is currently being tested in a number of field studies aimed at the: (i) measurement of GEM concentration gradients above both mercury-contaminated and background forest soils, (ii) quantification of vertical concentration gradients on a tower through a temperate deciduous forest canopy, and (iii) measurement of mercury concentration gradients over stable and thawing permafrost to determine the effect of permafrost degradation on GEM evasion. Contrasting with earlier flux studies, these investigations cover long time periods (up to 1.5 years) and have coarse temporal resolution (monthly to seasonally). Significant gradients of GEM air concentrations, both increasing and decreasing with height above ground, were observed, implying that at a minimum, the method is able to identify the flux direction of GEM. Under the right circumstances, this method can also be used to estimate the approximate magnitude of the GEM air-surface exchange flux. The measured gradients also reveal the impact of factors such as temperature, solar irradiance, and snow cover on air-surface exchange. The method holds promise for establishing the direction and size of exchange fluxes at long time scales of months to a year, especially in study areas where access, effort and cost are prohibitive to longer duration studies with existing approaches.&lt;/p&gt;

scholarly journals Seasonal changes in gaseous elemental mercury in relation to monsoon cycling over the northern South China Sea

2012 ◽  
Vol 12 (16) ◽  
pp. 7341-7350 ◽  
Author(s):  
C. M. Tseng ◽  
C. S. Liu ◽  
C. Lamborg
Keyword(s):  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Elemental Mercury ◽  
Source Tracking ◽  
Northeast Monsoon ◽  
Air Masses ◽  
Gaseous Elemental Mercury ◽  
China Sea ◽  
The Impact

Abstract. The distribution of gaseous elemental mercury (GEM) was determined in the surface atmosphere of the northern South China Sea (SCS) during 12 SEATS cruises between May 2003 and December 2005. The sampling and analysis of GEM were performed on board ship by using an on-line mercury analyzer (GEMA). Distinct annual patterns were observed for the GEM with a winter maximum of 5.7 ± 0.2 ng m−3 (n = 3) and minimum in summer (2.8 ± 0.2; n = 3), with concentrations elevated 2–3 times global background values. Source tracking through backward air trajectory analysis demonstrated that during the northeast monsoon (winter), air masses came from Eurasia, bringing continental- and industrial-derived GEM to the SCS. In contrast, during summer southwest monsoon and inter-monsoon, air masses were from the Indochina Peninsula and Indian Ocean and west Pacific Ocean. This demonstrates the impact that long-range transport, as controlled by seasonal monsoons, has on the Hg atmospheric distribution and cycling in the SCS.

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