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A measurement campaign was conducted on San Domino Island, part of the Tremiti Islands archipelago, located in Foggia, Italy. The area is almost entirely covered by vegetation, dominated by the following main species: Juniperus turbinata, Helichrysum italicum, Myrtus communis, Rosmarinus officinalis, Pistacia lentiscus and Pinus halepensis.This study focused on the BVOCs emitted by plants and the ground, employing a simple, economical, and efficient sampling and analysis method. The main known BVOC species emitted by Mediterranean plant species as α-pinene, β-pinene, camphene and limonene were detected. The measurements highlighted a daily complementarity between plant and soil emissions. The daily variations in BVOCs emitted by both plants and the soil are differ, ensuring an almost constant concentration throughout the day. At the same time, the composition of sea spray aerosol (SSA) was also measured.The measurement sites were selected based on botanical characterization to account for the predominant species on San Domino Island, and the sampling was conducted at human height to accurately identify the species for potential use.The combination of beneficial effects of the substances emitted by plant species and soil, along with the simultaneous presence of SSA, are factors that could enhance the effectiveness of forest therapy in a previously unexplored location.

Mercury (Hg) is a global pollutant that may potentially have serious impacts on human health and ecologies. The gaseous elemental mercury (GEM) exchanges between terrestrial surfaces and the atmosphere play important roles in the global Hg cycle. This study investigated GEM exchange fluxes over two land cover types (including Artemisia anethifolia coverage and removal and bare soil) using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The daily mean ambient levels of GEM and the total mercury concentrations of the soil (TSM) were determined to be 12.4 ± 3.6 to 16.4 ± 5.6 ng·m−3 and 32.8 to 36.2 ng·g−1, respectively, for all the measurements from May to September. The GEM exchange fluxes (ng·m−2·h−1) during the five-month period for the three treatments included the net emissions from the soil to the atmosphere (mean 5.4 to 7.1; range of −27.0 to 47.3), which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months (p < 0.05). In addition, it was determined that the Hg fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air relative humidity and soil moisture under all the conditions (p < 0.05). Overall, the results obtained in this study demonstrated that the grassland soil served as both a source and a sink for atmospheric Hg, depending on the season and meteorological factors. Furthermore, the plants played an important inhibiting role in the Hg exchanges between the soil and the atmosphere.

A measurement campaign was conducted on San Domino Island, part of the Tremiti Islands archipelago, located in Foggia, Italy. The area is almost entirely covered by vegetation, dominated by the following main species: Juniperus turbinata, Helichrysum italicum, Myrtus communis, Rosmarinus officinalis, Pistacia lentiscus and Pinus halepensis .This study focused on the BVOCs emitted by plants and the ground, employing a simple, economical, and efficient sampling and analysis method. The main known BVOC species emitted by Mediterranean plant species as α-pinene, β-pinene, camphene and limonene were detected. The measurements highlighted a daily complementarity between plant and soil emissions. The daily variations in BVOCs emitted by both plants and the soil are differ, ensuring an almost constant concentration throughout the day. At the same time, the composition of sea spray aerosol (SSA) was also measured. The measurement sites were selected based on botanical characterization to account for the predominant species on San Domino Island, and the sampling was conducted at human height to accurately identify the species for potential use. The combination of beneficial effects of the substances emitted by plant species and soil, along with the simultaneous presence of SSA, are factors that could enhance the effectiveness of forest therapy in a previously unexplored location., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

A common method for treating the aqueous phase (produced water) brought to the surface along with oil and natural gas is to discharge it into surface impoundments, also known as produced water ponds. Here we analyze data on the concentration of organic compounds in the water and on the flux of the same compounds into the atmosphere. Flux data extending from about 5 × 10 −2 to 10 +3 mg m −2 h −1 are consistent with mass-transfer laws given by the WATER9 semi-empirical algorithm, although empirical data display a noise level of about one order of magnitude and predictions by WATER9 are biased high. The data suggest partitioning between hydrocarbons in aqueous solution and in suspension, especially at higher overall concentrations. Salinity of the produced water does not have a detectable effect on hydrocarbon fluxes. Recently impounded waters are stronger emitters of hydrocarbons, while emissions of older waters are dominated by CO 2 . This aging effect can be explained by assuming, first, poor vertical mixing in the ponds, and second, gradual oxidation of hydrocarbons to CO 2 . Our measurements account for about 25% of the produced water ponds in the Uinta Basin, Eastern Utah, and when extrapolated to all ponds in the basin, account for about 4% to 14% of all organic compound emissions by the oil and natural gas sector of the basin, depending on the emissions inventory, and about 13% and 58%, respectively, of emissions of aromatics and alcohols. [ABSTRACT FROM AUTHOR]

This study assesses the mass transfer of compounds inside the US EPA flux hood, one of the enclosure devices most commonly employed for the direct measurement of atmospheric emissions from liquid surfaces in wastewater treatment plants (WWTPs). Experiments comprised the evaporation of water and the volatilisation of a range of volatile organic compounds (VOCs). Special attention was given to the evaluation of the mass transfer coefficients in the microenvironment created by the flux hood and the effects of concentration build up in the hood's headspace. The VOCs emission rates and the water evaporation rates generally increased with the sweep air flow rate, as did the mass transfer coefficients for all compounds. The emission of compounds whose volatilisation is significantly influenced by the gas phase was greatly affected by concentration build up, whereas this effect was not significant for liquid phase-controlled compounds. The gas-film mass transfer coefficient ( k G ) estimated inside the US EPA flux hood was of the same order as the respective k G reported in the literature for wind tunnel-type devices, but the emission rates measured by the flux hood can be expected to be lower, due to the concentration build-up. Compared against an emission model for the passive surfaces in WWTPs, the mass transfer of acetic acid (representing a gas phase-dominated compound) inside the US EPA flux hood was equivalent to conditions of wind speeds at 10 m height ( U 10 ) of 0.27, 0.51 and 0.99 m s −1 , respectively, for sweep air flow rates of 2, 5 and 10 L min −1 . On the other hand, for higher wind speeds, the emission rates of gas phase-controlled compounds obtained with the flux hood can be considerably underestimated: for instance, at U 10  = 5 m s −1 , the emission rates of acetic acid inside the flux hood would be approximately 23, 12 and 6 times lower than the emission rates in the field, for sweep air flow rates of 2, 5 and 10 L min −1 , respectively. A procedure is presented in order to scale the emission rates of these compounds measured with the flux hood to field conditions of higher winds. [ABSTRACT FROM AUTHOR]

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon ® dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0–34 cm) was identified by measuring total mercury in eight peat cores (57 ± 8 ng g −1 , average ± SE), vascular plant coverage (32–52%), water table level (4.5–14.1 cm) and dissolved gaseous elemental mercury concentrations (28–51 pg L −1 ) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, α = 0.05). Even though the correlation between the Teflon ® DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m −2 h −1 ) and REA (2 ng m −2 h −1 ) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers (<0.2 m 2 ) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity. [ABSTRACT FROM AUTHOR]

In order to reveal the mercury (Hg) emission and exchange characteristics at the soil-air interface under different vegetation cover types, the evergreen broad-leaf forest, shrub forest, grass, and bare lands of Simian Mountain National Nature Reserve were selected as the sampling sites. The gaseous elementary mercury (GEM) fluxes at the soil-air interface under the four vegetation covers were continuously monitored for two years, and the effect of temperature and solar radiation on GEM fluxes were also investigated. Results showed that the GEM fluxes at the soil-air interface under different vegetation cover types had significant difference (p < 0.05). The bare land had the maximum GEM flux (15.32 ± 10.44 ng.m-2.h-1), followed by grass land (14.73 ± 18.84 ng.m-2.h-1), and shrub forest (12.83 ± 10.22 ng.m-2.h-1), and the evergreen broad-leaf forest had the lowest value (11.23 ± 11.13 ng.m-2.h-1). The GEM fluxes at the soil-air interface under different vegetation cover types showed similar regularity in seasonal variation, which mean that the GEM fluxes in summer were higher than that in winter. In addition, the GEM fluxes at the soil-air interface under the four vegetation covers in Mt. Simian had obvious diurnal variations. [ABSTRACT FROM AUTHOR]

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.

Salt marshes are ecologically sensitive ecosystems where mercury (Hg) methylation and biomagnification can occur. Understanding the mechanisms controlling gaseous Hg flux from salt marshes is important to predict the retention of Hg in coastal wetlands and project the impact of environmental change on the global Hg cycle. We monitored Hg flux from a remote salt marsh over 9 days which included three cloudless days and a 4 mm rainfall event. We observed a cyclical diel relationship between Hg flux and solar radiation. When measurements at the same irradiance intensity are considered, Hg flux was greater in the evening when the sediment was warm than in the morning when the sediment was cool. This is evidence to suggest that both solar radiation and sediment temperature directly influence the rate of Hg(II) photoreduction in salt marshes. Hg flux could be predicted from solar radiation and sediment temperature in sub-datasets collected during cloudless days (R 2 = 0.99), and before (R 2 = 0.97) and after (R 2 = 0.95) the rainfall event, but the combined dataset could not account for the lower Hg flux after the rainfall event that is in contrast to greater Hg flux observed from soils after rainfall events. [ABSTRACT FROM AUTHOR]

Mercury exchange fluxes between atmosphere and soil surface were measured in two different types of soils; lawn soil (LS) and forest soil (FS). Average Hg emission from LS was higher than from FS although the soil Hg content was more than 2 times higher in forest soil. In LS, Hg emissions were much greater in warm season than in cold season; however, deposition was dominant in FS during warm season because of leafy trees blocking the solar radiation reaching on the soil surface. In both LS and FS, Hg fluxes showed significantly positive correlations with UV radiation and soil surface temperature during cold season. In addition, it was observed that emission showed positive correlation with UV radiation and soil temperature while there was negative relationship between deposition and UV radiation.

In order to reveal the mercury (Hg) emission and exchange characteristics at the soil–air interface under different vegetation cover types, the evergreen broad-leaf forest, shrub forest, grass, and bare lands of Simian Mountain National Nature Reserve were selected as the sampling sites. The gaseous elementary mercury (GEM) fluxes at the soil–air interface under the four vegetation covers were continuously monitored for two years, and the effect of temperature and solar radiation on GEM fluxes were also investigated. Results showed that the GEM fluxes at the soil–air interface under different vegetation cover types had significant difference (p < 0.05). The bare land had the maximum GEM flux (15.32 ± 10.44 ng·m−2·h−1), followed by grass land (14.73 ± 18.84 ng·m−2·h−1), and shrub forest (12.83 ± 10.22 ng·m−2·h−1), and the evergreen broad-leaf forest had the lowest value (11.23 ± 11.13 ng·m−2·h−1). The GEM fluxes at the soil–air interface under different vegetation cover types showed similar regularity in seasonal variation, which mean that the GEM fluxes in summer were higher than that in winter. In addition, the GEM fluxes at the soil–air interface under the four vegetation covers in Mt. Simian had obvious diurnal variations.

Mercury (Hg) emission and deposition can occur to and from soils, and are an important component of the global atmospheric Hg budget. This paper focuses on synthesizing existing surface-air Hg flux data collected throughout the Western North American region and is part of a series of geographically focused Hg synthesis projects. A database of existing Hg flux data collected using the dynamic flux chamber (DFC) approach from almost a thousand locations was created for the Western North America region. Statistical analysis was performed on the data to identify the important variables controlling Hg fluxes and to allow spatiotemporal scaling. The results indicated that most of the variability in soil-air Hg fluxes could be explained by variations in soil-Hg concentrations, solar radiation, and soil moisture. This analysis also identified that variations in DFC methodological approaches were detectable among the field studies, with the chamber material and sampling flushing flow rate influencing the magnitude of calculated emissions. The spatiotemporal scaling of soil-air Hg fluxes identified that the largest emissions occurred from irrigated agricultural landscapes in California. Vegetation was shown to have a large impact on surface-air Hg fluxes due to both a reduction in solar radiation reaching the soil as well as from direct uptake of Hg in foliage. Despite high soil Hg emissions from some forested and other heavily vegetated regions, the net ecosystem flux (soil flux + vegetation uptake) was low. Conversely, sparsely vegetated regions showed larger net ecosystem emissions, which were similar in magnitude to atmospheric Hg deposition (except for the Mediterranean California region where soil emissions were higher). The net ecosystem flux results highlight the important role of landscape characteristics in effecting the balance between Hg sequestration and (re-)emission to the atmosphere. [ABSTRACT FROM AUTHOR]

Enclosure devices have been studied and used for research purposes and practical applications in order to measure the emission rate of odorous pollutants from quiescent liquid surfaces to atmosphere. However, important questions remain about the interference of these measuring devices on the actual emission rate. The main concern regarding the use of a flux chamber is the fact that odorous compounds can accumulate into the chamber and yield gas-phase concentration increase inside the equipment, which causes a reduction of the emission rate during the measurement and thus gives an inaccurate local emission rate. Furthermore, the fluid flow inside the chamber does not reproduce the atmospheric boundary layer flow. This study applied the Computational Fluid Dynamics (CFD) technique in order to investigate the influence of the fluid flow features inside a flux chamber on the measured hydrogen sulfide emission rate at quiescent liquid surfaces. The flux chamber design and operational conditions are those supported by the United States Environmental Protection Agency (US EPA). The results show that the US EPA flux chamber presents a fairly well mixed air phase. However, a trend to stagnation and hydrogen sulfide accumulation near chamber walls was detected in the computational simulation, which also indicated that the positioning of the sampling tube in relation to the inlet orifices may lead to deviations in the measurement results. CFD results showed that the wall shear and concentration gradients spatially vary at the gas–liquid interface, and friction velocity inside the chamber does not match typical values of atmospheric flow. [ABSTRACT FROM AUTHOR]

A simulative mesocosm study was conducted to evaluate the influence of wet–dry rotation on mercury (Hg) flux from soil/water to air and the distribution of Hg species in water as well as Hg chemical fractions in soil. Three types of soil were employed including two kinds of paddy soil, Typic Purpli-Udic Cambosols (TPUC) and Xanthi-Udic Ferralosols (XUF), as well as the Alluvial Soil (AS) from Three Gorge reservoir area in Chongqing, China. The results showed that Hg fluxes in wetting periods were significantly higher than that in drying periods. It might be due to the formation of a layer of stable air over the water surface in which some redox reactions promote evasion processes over the water surface. This result indicated that more Hg would be evaporated from the Three Gorge reservoir and paddy soil field during the flooding season. Hg fluxes were positively correlated with air temperature and solar irradiation, while negatively correlated with air humidity and the electronic conductivity of water. Hg fluxes from AS and TPUC were significantly higher than that from XUF, which might be due to the higher organic matter (OM) contents in XUF than TPUC and AS. The reduction processes of oxidized Hg were restrained due to the strong binding of Hg to OM, resulting in the decrease in Hg flux from the soil. [ABSTRACT FROM AUTHOR]

Abstract: A number of mechanisms have been shown to facilitate the flux of mercury from soils, although at sub-zero temperatures, there is evidence to suggest that alternate mechanisms may exist. Field studies at sub-zero temperatures have observed spikes in flux under certain conditions however very little laboratory work has been done to characterize the specific effects or mechanisms. A Dynamic Flux Chamber (DFC) and Tekran Model 2537A were used to analyse mercury flux from a naturally enriched soil. Soil moisture contents were varied between 30%, 60%, and 75% of field capacity while temperatures were cycled between 0 and −25 °C. The results, which were compared to room temperature baseline runs, showed that, at sub-zero temperatures, the mercury flux was suppressed in general. However, during the temperature cycling runs, soil flux spikes were evident during positive temperature change or warming. A one-way ANOVA by ranks proved that statistically significant fluxes were occurring during the runs at 30% and 60% of field capacity for positive rates of temperature changes. Arrhenius plots showed that for positive soil temperatures flux and temperature correlated well with the Arrhenius relationship. At sub-zero conditions however, no relationship was present, indicating another mechanism was present. The proposed mechanism for this enhanced flux is the physical evacuation of interstitial pore space gaseous mercury by the expansion and contraction of the freeze–thaw cycle. [Copyright &y& Elsevier]

Abstract: Dynamic Flux Chambers (DFCs) are commonly applied for the measurement of non-point source mercury (Hg) emissions from a wide range of surfaces. A standard operating protocol and design for DFCs does not exist, and as a result there is a large diversity in methods described in the literature. Because natural and anthropogenic non-point sources are thought to contribute significantly to the atmosphere Hg pool, development of accurate fluxes during field campaigns is essential. The objective of this research was to determine how differences in chamber material, sample port placement, vertical cross sectional area/volume, and flushing flow rate influence the Hg flux from geologic materials. Hg fluxes measured with a Teflon chamber were higher than those obtained using a polycarbonate chamber, with differences related to light transmission and substrate type. Differences in sample port placement (side versus top) did not have an influence on Hg fluxes. When the same flushing flow rate was applied to two chambers of different volumes, higher fluxes were calculated for the chamber with the smaller volume. Conversely, when two chambers with different volumes were maintained at similar turnover times, the larger volume chamber yielded higher Hg fluxes. Overall, the flushing flow rate and associated chamber turnover time had the largest influence on Hg flux relative to the other parameters tested. Results from computational fluid dynamic (CFD) modeling inside a DFC confirm that the smaller diffusion resistance at higher flushing flows contributes to the higher measured flux. These results clearly illustrate that differences in chamber design and operation can significantly influence the resulting calculated Hg flux, and thus impact the comparability of results obtained using DFC designs and/or operating parameters. A protocol for determining a flushing flow rate that results in fluxes less affected by chamber operating conditions and design is proposed. Application of this protocol would provide a framework for comparison of data from different studies. [Copyright &y& Elsevier]

Mercury (Hg) emissions from the soils taken from two different sites (deciduous and coniferous forests) in the Adirondacks were measured in outdoor and laboratory experiments. Some of the soil samples were irradiated to eliminate biological activity. The result from the outdoor measurements with different soils suggests the Hg emission from the soils is partly limited by fallen leaves covering the soils which helps maintain relatively high soil moisture and limits the amount of heat and solar radiation reaching the soil surface. In laboratory experiments exposure to UV-A (365nm) had no significant effect on the Hg emissions while the Hg emissions increased dramatically during exposure to UV-B (302nm) light suggesting UV-B directly reduced soil-associated Hg. Overall these results indicate that for these soils biotic processes have a relatively constant and smaller influence on the Hg emission from the soil than the more variable abiotic processes. [Copyright &y& Elsevier]

Lakes in temperate regions stratify during summer and winter months, creating distinct layers of water differentiated by their physical and chemical characteristics. When lakes mix in autumn and spring, mercury cycling may be affected by the chemical changes that occur during mixing. Sampling was conducted in Lake Lacawac, Eastern Pennsylvania, USA, throughout the autumn of 2007 to characterize changes in emission of gaseous elemental mercury (Hg0) from the lake surface and dissolved mercury profiles in the water column during mixing. Water chemistry and weather parameters were also measured, including dissolved organic carbon (DOC), iron, and solar radiation which have been shown to interact with mercury species. Results indicate that emission of Hg0 from the lake to the atmosphere during turnover was controlled both by solar radiation and by surface water mercury concentration. As autumn turnover progressed through the months of October and November, higher mercury concentration water from the hypolimnion mixed with epilimnetic water, increasing mercury concentration in epilimnetic waters. Dissolved absorbance was significantly correlated with mercury concentrations and with iron, but DOC concentrations were essentially constant throughout the study period and did not exhibit a relationship with either dissolved mercury concentrations or emission rates. Positive correlations between dissolved mercury and iron and manganese also suggest a role for these elements in mercury transport within the lake, but iron and manganese did not demonstrate a relationship with emission rates. This research indicates that consideration of seasonal processes in lakes is important when evaluating mercury cycling in aquatic systems. [Copyright &y& Elsevier]

This study focused on characterizing air–surface mercury Hg exchange for individual surfaces (soil, litter-covered soil and plant shoots) and ecosystem-level flux associated with tallgrass prairie ecosystems housed inside large mesocosms over three years. The major objectives of this project were to determine if individual surface fluxes could be combined to predict ecosystem-level exchange and if this low-Hg containing ecosystem was a net source or sink for atmospheric Hg. Data collected in the field were used to validate fluxes obtained in the mesocosm setting. Because of the controlled experimental design and ease of access to the mesocosms, data collected allowed for assessment of factors controlling flux and comparison of models developed for soil Hg flux versus environmental conditions at different temporal resolution (hourly, daily and monthly). Evaluation of hourly data showed that relationships between soil Hg flux and environmental conditions changed over time, and that there were interactions between parameters controlling exchange. Data analyses demonstrated that to estimate soil flux over broad temporal scales (e.g. annual flux) coarse-resolution data (monthly averages) are needed. Plant foliage was a sink for atmospheric Hg with uptake influenced by plant functional type and age. Individual system component fluxes (bare soil and plant) could not be directly combined to predict the measured whole system flux (soil, litter and plant). Emissions of Hg from vegetated and litter-covered soil were lower than fluxes from adjacent bare soil and the difference between the two was seasonally dependent and greatest when canopy coverage was greatest. Thus, an index of plant canopy development (canopy greenness) was used to model Hg flux from vegetated soil. Accounting for ecosystem Hg inputs (precipitation, direct plant uptake of atmospheric Hg) and modeled net exchange between litter-and-plant covered soils, the tallgrass prairie was found to be a net annual sink of atmospheric Hg. [Copyright &y& Elsevier]

Abstract: An investigation was conducted to estimate mercury emission to the atmosphere from different environmental surfaces and to assess its contribution to the local mercury budget in Chongqing, China. Mercury flux was measured using dynamic flux chamber (DFC) at six soil sites of three different areas (mercury polluted area, farmland and woodland) and four water surfaces from August 2003 to April 2004. The mercury emission fluxes were 3.5±1.2–8.4±2.5ngm−2 h−1 for three shaded forest sites, 85.8±32.4ngm−2 h−1 for farming field, 12.3±9.8–733.8±255ngm−2 h−1 for grassland sites, and 5.9±12.6–618.6±339ngm−2 h−1 for water surfaces. Mercury exchange fluxes were generally higher from air/water surfaces than from air/soil surfaces. The mercury negative fluxes were found in tow soil sites at overcast days (mean=−6.4±1.5ngm−2 h−1). The diurnal and seasonal variations of mercury flux were observed in all sites. The mercury emission responded positively to the solar radiation, but negatively to the relative humidity. The mercury flux from air/soil surfaces was significantly correlated with soil temperature, which was well described by an Arrhenius-type expression with activation energy of 31.1kcalmol−1. The annual mercury emission to the atmosphere from land surface is about 1.787t of mercury in Chongqing. [Copyright &y& Elsevier]

Understanding the interactions between the environment and emissions from livestock manure is essential in developing management practices intended to minimize negative environmental consequences. However, protocols arid equipment necessary to investigate these interactions at the laboratory or field-scale are cumbersome and can be expensive. An inexpensive dynamic flux chamber (cost < $400 per unit) was designed to measure gaseous emissions from cattle manure in laboratory and field experiments. The hemispherical stainless steel chamber (emission surface = 0.08 m2) was constructed with an internal gas mixing fan. A port was attached to the chamber top, which facilitated the collection of headspace gas samples for greenhouse gases and volatile organic compounds (VOC) by solid-phase microextraction (SPME). The chamber was tested to evaluate flow characteristics and was found to perform very similarly to a continuous -flow stirred reactor As such, concentrations measured at the sampling port were indicative of concentrations anywhere in the headspace, ht laboratory and field applications, the inexpensive dynamic flux chamber was easy to use and required little operator input to quickly obtain multiple samples to measure the relative emissions of greenhouse gases, ammonia (NH3), and VOC from multiple sites in cattle feedlot pens. [ABSTRACT FROM AUTHOR]

Abstract: Increases in mercury volatilization from naturally enriched soils due to precipitation events have been observed in the field [Lindberg et al., 1999. Journal of Geophysical Research 104(D17), 21879–21888; Poissant et al., 1999. Journal of Geophysical Research 104(D17), 21845–21857] and indicate that further research on the exact mechanisms responsible for the increased fluxes are required. In this research, the effects of precipitation on Hg fluxes are simulated in a controlled laboratory experiment using a dynamic flux chamber system coupled with an internal precipitation generator and soil lysimeter. The experimental results indicate a sharp and rapid spike in the Hg(0) flux during the precipitation event which is due, in part, to the physical displacement of the Hg-containing interstitial soil air by the infiltrating rain water. After the precipitation event, the soil moisture prior to the event plays an important role in the Hg(0) emissions. When the soil is initially fairly dry (5–6vol%), an enhancement in Hg(0) flux on the order of 12–16 times is observed after the precipitation event. However, when the soil is initially relatively moist (>15vol%), no enhancement in the Hg(0) flux after the precipitation event is observed. This enhancement in the Hg(0) flux is well-correlated to the soil moisture before a rain event using a decaying exponential function. [Copyright &y& Elsevier]

Air/surface exchange of mercury was investigated over background soils at five sites in the Tahquamenon River watershed in the Michigan Upper Peninsula in the summer of 1998. Measurements of Hg fluxes were performed during midday periods using the ORNL Teflon dynamic flux chamber. Mean Hg emission fluxes were 1.4±0.3–2.4±1.0 ng m-2 hr-1 for three shaded forest sites and 7.6±1.7 ng m-2 hr-1 for an open field site. Hg dry deposition was observed at a heavily shaded forest site over wet soils (mean = –0.3±0.2 ng m-2 hr-1). The overall mean Hg flux was 1.4±1.4 ng m-2 hr-1 for the four shaded forest sites. The Hg fluxes observed at these sites are similar to those found at other northern background sites. Significant, rapid response of Hg emission to solar radiation was observed over these background soils. Artificial irrigation over these soils induced immediate and measurable increases in Hg emission. Soil temperature was found to be less influential to Hg air/surface exchange over these heavily shaded forest background soils than we have seen elsewhere. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigated the gaseous elemental mercury exchange fluxes over Artemisia anethifolia coverage and removal and bare soil using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The results showed that the net emissions from the soil to the atmosphere, which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months. In addition, it was determined that the mercury fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air humidity and soil moisture. The grassland soil served as both a source and a sink for atmospheric mercury, depending on the season and meteorological factors. The plants played an important inhibiting role in the mercury exchanges between the soil and the atmosphere. This research will potentially assist in the development of more accurate local and regional estimates of mercury emissions from degraded grassland areas and the terrestrial environment as a whole. Mercury (Hg) is a global pollutant that may potentially have serious impacts on human health and ecologies. The gaseous elemental mercury (GEM) exchanges between terrestrial surfaces and the atmosphere play important roles in the global Hg cycle. This study investigated GEM exchange fluxes over two land cover types (including Artemisia anethifolia coverage and removal and bare soil) using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The daily mean ambient levels of GEM and the total mercury concentrations of the soil (TSM) were determined to be 12.4 ± 3.6 to 16.4 ± 5.6 ng·m−3 and 32.8 to 36.2 ng·g−1, respectively, for all the measurements from May to September. The GEM exchange fluxes (ng·m−2·h−1) during the five-month period for the three treatments included the net emissions from the soil to the atmosphere (mean 5.4 to 7.1; range of −27.0 to 47.3), which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months (p < 0.05). In addition, it was determined that the Hg fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air relative humidity and soil moisture under all the conditions (p < 0.05). Overall, the results obtained in this study demonstrated that the grassland soil served as both a source and a sink for atmospheric Hg, depending on the season and meteorological factors. Furthermore, the plants played an important inhibiting role in the Hg exchanges between the soil and the atmosphere. [ABSTRACT FROM AUTHOR]

A year-long field study of mercury (Hg) air/water exchange was conducted at a southern reservoir lake, Cane Creek Lake (Cookeville, TN, USA). The Hg air/water exchange fluxes and meteorological data including solar radiation (global solar radiation, Rg and ultraviolent radiation, UVA), water and air temperatures, relative humidity, and wind speed were collected to study the daily and seasonal trends of the Hg air/water exchange at the lake in relation to solar radiation and wind speed. The Hg exchange fluxes generally exhibited diurnal patterns with a rise in the morning, a peak around noontime, and a fall in the afternoon through the evening, closely following the change of solar radiation. There were cases that deviated from this general daily trend. The Hg emission fluxes were all below 3 ng m−2 h−1 with the daily mean fluxes < 2 ng m−2 h−1. The fluxes in the summer (mean: 1.2 ng m−2 h−1) were higher than in the fall (mean: 0.6 ng m−2 h−1) and winter (mean: 0.7 ng m−2 h−1). The daily and seasonal trends of the Hg air/water exchange fluxes are similar to the trends of the changes of the dissolved gaseous mercury (DGM) concentrations in the lake observed in our previous study. Solar radiation was found to exert a primary control over the Hg air/water exchange, while wind speed appeared to have a secondary effect on the Hg exchange. The two-thin-film model was used to calculate Hg emission fluxes from the Cane Creek Lake water. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Enclosure devices have been studied and used for research purposes and practical applications in order to measure the emission rate of odorous pollutants from quiescent liquid surfaces to atmosphere. However, important questions remain about the interference of these measuring devices on the actual emission rate. The main concern regarding the use of a flux chamber is the fact that odorous compounds can accumulate into the chamber and yield gas-phase concentration increase inside the equipment, which causes a reduction of the emission rate during the measurement and thus gives an inaccurate local emission rate. Furthermore, the fluid flow inside the chamber does not reproduce the atmospheric boundary layer flow. This study applied the Computational Fluid Dynamics (CFD) technique in order to investigate the influence of the fluid flow features inside a flux chamber on the measured hydrogen sulfide emission rate at quiescent liquid surfaces. The flux chamber design and operational conditions are those supported by the United States Environmental Protection Agency (US EPA). The results show that the US EPA flux chamber presents a fairly well mixed air phase. However, a trend to stagnation and hydrogen sulfide accumulation near chamber walls was detected in the computational simulation, which also indicated that the positioning of the sampling tube in relation to the inlet orifices may lead to deviations in the measurement results. CFD results showed that the wall shear and concentration gradients spatially vary at the gas-liquid interface, and friction velocity inside the chamber does not match typical values of atmospheric flow., (Copyright © 2015 Elsevier Ltd. All rights reserved.)