scholarly journals Review comments on "First eddy covariance flux measurements of gaseous elemental mercury (Hg0) over a grassland" by Osterwalder et al.

2019 ◽  
Author(s):  
Anonymous
Keyword(s):  
Eddy Covariance ◽  
Elemental Mercury ◽  
Gaseous Elemental Mercury ◽  
Flux Measurements

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.

scholarly journals Eddy Covariance Flux Measurements of Gaseous Elemental Mercury Using Cavity Ring-Down Spectroscopy

2015 ◽  
Vol 49 (3) ◽  
pp. 1559-1568 ◽  
Author(s):  
Ashley M. Pierce ◽  
Christopher W. Moore ◽  
Georg Wohlfahrt ◽  
Lukas Hörtnagl ◽  
Natascha Kljun ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Elemental Mercury ◽  
Cavity Ring Down Spectroscopy ◽  
Gaseous Elemental Mercury ◽  
Flux Measurements ◽  
Cavity Ring Down

First eddy covariance flux measurements of gaseous elemental mercury over a grassland

2020 ◽  
Author(s):  
Stefan Osterwalder ◽  
Werner Eugster ◽  
Iris Feigenwinter ◽  
Martin Jiskra
Keyword(s):  
Detection Limit ◽  
Eddy Covariance ◽  
Net Ecosystem Exchange ◽  
Elemental Mercury ◽  
Terrestrial Ecosystems ◽  
Global Scale ◽  
Gaseous Elemental Mercury ◽  
Direct Measurements ◽  
The Us ◽  
Flux Measurements

&lt;p&gt;Direct measurements of the net ecosystem exchange (NEE) of gaseous elemental mercury (Hg&lt;sup&gt;0&lt;/sup&gt;) are crucial to improve our understanding of global Hg cycling and ultimately Hg exposure in humans and wildlife. The lack of long-term, ecosystem-scale measurements causes large uncertainties in Hg&lt;sup&gt;0&lt;/sup&gt; flux estimates. Today it remains unclear whether terrestrial ecosystems are net sinks or sources of atmospheric Hg&lt;sup&gt;0&lt;/sup&gt;. Here, we present the first successful eddy covariance NEE measurements of Hg&lt;sup&gt;0&lt;/sup&gt; over natural, low-Hg soils (41 - 75 ng Hg g&lt;sup&gt;-1&lt;/sup&gt; topsoil [0-10 cm]) at a managed grassland site in Chamau, Switzerland. We present a detailed validation of the eddy covariance technique for Hg&lt;sup&gt;0&lt;/sup&gt; 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&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt; (maximum) with a 50 % cut-off at 0.074 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt;. The statistical estimate of the Hg&lt;sup&gt;0&lt;/sup&gt; flux detection limit under real-world outdoor conditions at the site was 5.9 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt; (50 % cut-off). Based on our analysis we give suggestions to further improve the precision of the system and pinpoint challenges and interferences that occurred during the 34-day pilot campaign in summer 2018. The data were obtained during extremely hot and dry meteorological conditions. We estimated a net summertime grassland-atmosphere Hg&lt;sup&gt;0&lt;/sup&gt; flux from -0.6 to 7.4 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt; (range between 25&lt;sup&gt;th&lt;/sup&gt; and 75&lt;sup&gt;th&lt;/sup&gt; percentiles). The measurements revealed a distinct diel pattern with lower nighttime fluxes (1.0 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt;) compared to daytime fluxes (8.4 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt;). Drought stress during the campaign induced partial stomata closure of vegetation leading to a midday depression in CO&lt;sub&gt;2&lt;/sub&gt; uptake, which did not recover during the afternoon. We suggest that partial stomata closure dampened Hg&lt;sup&gt;0&lt;/sup&gt; uptake by vegetation as well, resulting in a NEE of Hg&lt;sup&gt;0&lt;/sup&gt; dominated by soil emission. The new Eddy Mercury system seems suitable to complement existing research infrastructures such as ICOS RI in Europe or NOAA Observing Systems in the US built to calculate greenhouse gas balances with direct Hg&lt;sup&gt;0&lt;/sup&gt; deposition and emission measurements. We anticipate our Eddy Mercury system to improve knowledge about Hg cycling between ecosystems and the atmosphere and to challenge model simulations on a regional and global scale.&lt;/p&gt;

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 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 Fluxes of gaseous elemental mercury (GEM) in the High Arctic during atmospheric mercury depletion events (AMDEs)

2018 ◽  
Vol 18 (9) ◽  
pp. 6923-6938 ◽  
Author(s):  
Jesper Kamp ◽  
Henrik Skov ◽  
Bjarne Jensen ◽  
Lise Lotte Sørensen
Keyword(s):  
Eddy Covariance ◽  
Elemental Mercury ◽  
Atmospheric Temperature ◽  
High Arctic ◽  
Atmospheric Mercury ◽  
Research Station ◽  
Co2 Fluxes ◽  
Gaseous Elemental Mercury ◽  
Surface Snow ◽  
North Greenland

Abstract. Measurements of gaseous elemental mercury (GEM) fluxes over snow surfaces using a relaxed eddy accumulation (REA) system are carried out at the High Arctic site at the Villum Research Station, Station Nord, in North Greenland. Simultaneously, CO2 fluxes are determined using the eddy covariance (EC) technique. The REA system with dual inlets and dual analyzers is used to measure fluxes directly over the snow. The measurements were carried out from 23 April to 12 May during spring 2016, where atmospheric mercury depletion events (AMDEs) took place. The measurements showed a net emission of 8.9 ng m−2 min−1, with only a few minor episodes of net depositional fluxes, from a maximum deposition of 8.1 ng m−2 min−1 to a maximum emission of 179.2 ng m−2 min−1. The data support the theory that gaseous oxidized mercury (GOM) is deposited during AMDEs followed by formation of GEM on surface snow and is re-emitted as GEM shortly after the AMDEs. Furthermore, observation of the relation between GEM fluxes and atmospheric temperature suggests that GEM emission partly could be affected by surface heating. However, it is also clear that the GEM emissions are affected by many parameters.

Determination of gaseous elemental mercury air-sea exchange in the Baltic Sea

2020 ◽  
Author(s):  
Stefan Osterwalder ◽  
Michelle Nerentorp ◽  
Wei Zhu ◽  
Erik Nilsson ◽  
Mats Nilsson ◽  
...  
Keyword(s):  
Wind Speed ◽  
Baltic Sea ◽  
Elemental Mercury ◽  
The Baltic Sea ◽  
Transfer Velocity ◽  
Field Station ◽  
Gaseous Elemental Mercury ◽  
Starting Point ◽  
Flux Measurements ◽  
The Baltic

&lt;p&gt;Ocean waters store approximately 400 Gg of mercury (Hg) and exchange it with the atmosphere at a high rate. Air-sea exchange of gaseous elemental mercury (Hg&lt;sup&gt;0&lt;/sup&gt;) is a key process in global Hg cycling because evasion lowers the reservoir of Hg(II) available for methylation and subsequent bioaccumulation in marine fish and prolongs the atmospheric lifetime and subsequently global cycling of Hg. However, global estimates on the air-sea flux are not well constrained (1.9 to 4.2 Gg a&lt;sup&gt;-1&lt;/sup&gt;) mainly because high-resolution measurements of Hg&lt;sup&gt;0&lt;/sup&gt; in seawater are largely lacking and parameterization of the Hg&lt;sup&gt;0&lt;/sup&gt; transfer velocity introduces uncertainties in Hg&lt;sup&gt;0&lt;/sup&gt; flux modelling. We present estimates of the net Hg&lt;sup&gt;0&lt;/sup&gt; flux for the Baltic Sea derived from land-based marine measurements of Hg&lt;sup&gt;0&lt;/sup&gt; in air and seawater as well as micrometeorological techniques. We found that coastal waters at the ICOS field station &amp;#214;stergarnsholm, located east of Gotland, Sweden, were typically supersaturated with seawater Hg&lt;sup&gt;0&lt;/sup&gt; (mean &amp;#177; SD = 13.5 &amp;#177; 3.5 ng m&lt;sup&gt;-3&lt;/sup&gt;; ca. 10 % of total Hg) compared to ambient Hg&lt;sup&gt;0&lt;/sup&gt; (1.3 &amp;#177; 0.2 ng m&lt;sup&gt;-3&lt;/sup&gt;). The Hg&lt;sup&gt;0&lt;/sup&gt; flux calculated using gas-transfer wind speed relationships ranged from 0.1 to 1.3 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt; over the course of the campaign (May 10 &amp;#8211; June 20, 2017). The modeled Hg&lt;sup&gt;0&lt;/sup&gt; flux showed a distinct diel pattern with an average daytime flux of 0.6 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt; and nighttime flux of 0.4 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt;, indicating that temperature and light induced production of seawater Hg&lt;sup&gt;0&lt;/sup&gt; was of significance in shallow waters. Preliminary calculations of the average coastal Hg&lt;sup&gt;0&lt;/sup&gt; flux simultaneously measured using direct, non-intrusive gradient-based, aerodynamic gradient and relaxed eddy accumulation techniques were 0.5 &amp;#177; 1, 0.6 &amp;#177; 3.8 and 0.6 &amp;#177; 37 ng m&lt;sup&gt;-2&lt;/sup&gt; h&lt;sup&gt;-1&lt;/sup&gt;, respectively. Although, these flux estimates were in good agreement, there were indications in the temporal patters of the observations, which suggest that there is a need to reconsider the modeled flux with the support of more direct flux measurements. Direct flux measurements revealed not only Hg&lt;sup&gt;0&lt;/sup&gt; evasion but also periods of Hg&lt;sup&gt;0&lt;/sup&gt; dry deposition. In addition, direct measurements indicated a stronger wind speed dependence of the Hg&lt;sup&gt;0&lt;/sup&gt; transfer velocity compared to CO&lt;sub&gt;2&lt;/sub&gt; which appears to coincide with whitecap formation in the open sea flux footprint (wind speed &gt; 5 m s&lt;sup&gt;-1&lt;/sup&gt;). Hence, we anticipate this study as a starting point for more land-based, marine, continuous measurements of seawater Hg&lt;sup&gt;0&lt;/sup&gt; concentration in combination with micrometeorological fluxes in order to improve Hg&lt;sup&gt;0&lt;/sup&gt; flux estimates in regional and global scale models. In this context, directly measured Hg&lt;sup&gt;0&lt;/sup&gt; fluxes will be pivotal to improve transfer velocity estimates of Hg&lt;sup&gt;0&lt;/sup&gt; especially during periods of high wind speed.&lt;/p&gt;

scholarly journals Air Concentrations of Gaseous Elemental Mercury and Vegetation–Air Fluxes within Saltmarshes of the Tagus Estuary, Portugal

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 228
Author(s):  
Rute Cesário ◽  
Nelson J. O’Driscoll ◽  
Sara Justino ◽  
Claire E. Wilson ◽  
Carlos E. Monteiro ◽  
...  
Keyword(s):  
Leaf Area ◽  
Elemental Mercury ◽  
Ambient Air ◽  
Tagus Estuary ◽  
Contaminated Site ◽  
Gaseous Elemental Mercury ◽  
Mercury Flux ◽  
Sarcocornia Fruticosa ◽  
Air Concentrations

In situ air concentrations of gaseous elemental mercury (Hg(0)) and vegetation–atmosphere fluxes were quantified in both high (Cala Norte, CN) and low-to-moderate (Alcochete, ALC) Hg-contaminated saltmarsh areas of the Tagus estuary colonized by plant species Halimione portulacoides (Hp) and Sarcocornia fruticosa (Sf). Atmospheric Hg(0) ranged between 1.08–18.15 ng m−3 in CN and 1.18–3.53 ng m−3 in ALC. In CN, most of the high Hg(0) levels occurred during nighttime, while the opposite was observed at ALC, suggesting that photoreduction was not driving the air Hg(0) concentrations at the contaminated site. Vegetation–air Hg(0) fluxes were low in ALC and ranged from −0.76 to 1.52 ng m−2 (leaf area) h−1 for Hp and from −0.40 to 1.28 ng m−2 (leaf area) h−1 for Sf. In CN, higher Hg fluxes were observed for both plants, ranging from −9.90 to 15.45 ng m−2 (leaf area) h−1 for Hp and from −8.93 to 12.58 ng m−2 (leaf area) h−1 for Sf. Mercury flux results at CN were considered less reliable due to large and fast variations in the ambient air concentrations of Hg(0), which may have been influenced by emissions from the nearby chlor-alkali plant, or historical contamination. Improved experimental setup, the influence of high local Hg concentrations and the seasonal activity of the plants must be considered when assessing vegetation–air Hg(0) fluxes in Hg-contaminated areas.

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