Katarina Gårdfeldt

Intercomparison of methods for sampling and analysis of atmospheric mercury species

An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.

Atmospheric mercury distribution in Northern Europe and in the Mediterranean region

Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.

Oxidation of atomic mercury by hydroxyl radicals and photoinduced decomposition of methylmercury in the aqueous phase

Abstract The rate constant for Hg 0 + . OH , k Hg 0 + . OH =(2.4±0.3)×10 9 M −1 s −1 , in the aqueous phase was determined using a relative rate technique with methyl mercury as reference compound. The .OH initiated mercury reaction proceeds via the molecular Hg(I) radical which is oxidised to Hg(II) by dissolved O2. The reaction can be of importance under certain atmospheric circumstances, such as when the aqueous phase capacity of forming OH radicals is significant and the gas phase concentration of ozone drops. The same end product, i.e. Hg(II) was observed from the photodegradation of methylmercury hydroxide. In this case, molecular Hg(I) radicals are again likely to be formed after photodegradation of the Hg–C bond with subsequent oxidation. A lifetime of 230 h of methylmercury at outdoor conditions was estimated due to this reaction. The action of .OH on methylmercury species also involves breaking of organometallic bonds and formation of Hg(II). Speciation of these reaction products from methylmercury is important for the estimation of biogeochemical cycling of mercury.

A kinetic study on the abiotic methylation of divalent mercury in the aqueous phase

The mechanism and kinetics of the formation of methylmercury from an experimental solution containing divalent mercury and acetic acid has been investigated. The experiments were performed in a 2-dm(3) Teflon reactor. The organic mercury was measured with time resolutions varying between minutes and hours, after derivatisation, gas chromatography separation and Cold vapour atomic fluorescence detection. (GC)-CVAFS. CVAFS technique was used for determination of inorganic mercury in the aqueous phase using an automated mercury analyser. The experiments were carried out in concentrations relevant for natural waters. Our result shows that the reaction proceeds via mercury acetate complexes. A first order reaction coefficient has been calculated at various pH values, and was found to be (9.0+/-0.9) x 10(-7) s(-1) at pH 3.6-3.7. The rate was not found to be enhanced by UV-light when taking into account the photolytical degradation of methylmercury. The reaction rate at various pH values, the influences of some other relevant reaction parameters, and implications for atmospheric and terrestrial waters are discussed.

Total gaseous mercury exchange between air and water at river and sea surfaces in Swedish coastal regions

This study includes five intensive field measurement campaigns. Four of the campaigns were performed over seawater surface during the summer and winter of 1997 and the summer of 1998 at Kristineberg Marine Research Station (KMRS). The fifth campaign was conducted over a river surface during the summer of 1999 at Knobesholm in southwestern Sweden. The major purpose of these campaigns was to determine emissions of mercury from natural waters in northern Europe. The influence of some physical parameters, i.e. temperature in water and air, relative humidity and solar radiation were also examined. Dynamic flux chamber technique coupled with automatic mercury vapour-phase analysers (Gardis 1A or Tekran 2357) was used. Both sites show net evasion during summer season, however, the surficial evasion rate of the river is more than one order of magnitude higher than that of the seawater. The high content of organic matter in the river in conjunction with strong insolation and subsequent water temperature variations may explain the high mercury evasion measured at the river site. An average evasion of þ11 ng m � 2 h � 1 (varying from � 2: 5t oþ88: 9n g m � 2 h � 1 ) was obtained during the course of the river measurement. At the sea site, mercury evasion was found in the interval between � 2:72 and þ8:84 ng m � 2 h � 1 with an average evasion of þ0:61 ng m � 2 h � 1 . Mercury evasion measured over both river and seawater surfaces exhibits a consistently diurnal pattern with maximum evasion during the daytime period and minimum evasion during the nighttime period. At the freshwater site, mercury evasion is strongly correlated with the intensity of net insolation, and negatively correlated with relative humidity. An exponential relationship between mercury evasion and water temperature was also observed at the freshwater measurement site. At the seawater site, a strong correlation between mercury evasion and intensity of UVA part of insolation was obtained. Insolation is speculated to play an important role in the formation of dissolved gaseous mercury in both river and seawater. # 2001 Elsevier Science Ltd. All rights reserved.

Determination of Henry’s law constant for elemental mercury

The assessment of the global mercury cycle involves estimations of the evasion of mercury form oceanic waters. In such estimations Henrys law constant is often used. In this study the Henrys law constant for elemental mercury has been re-determined in MQ water and artificial sea water. Moreover, for the first time it has been determined for 1.5M sodium chloride (NaCl) solution which is of relevance for modeling of atmospheric waters at coastal locations. For all solutions, experiments has been conducted at five different temperatures between 278 and 308K, using a novel technique, for mercury, based on direct measurements of the portioning of mercury between the aqueous and gaseous phase. Elemental mercury was extracted from the water column and the logarithm of the mass of extracted mercury was plotted against time. A dimensionless Henrys law constant, defined as: [see text] was obtained from the slope of the curve. Almost no difference was observed in the values comparing the Milli-Q water and artificial sea water, however for the 1.5M NaCl solution a salting-out effect was seen, i.e. the solubility of mercury in the water phase decreased. The decreased solubility will generate an increase in the value of Henrys law constant.

Distribution of atmospheric mercury species in Northern Europe: Final results from the MOE-project

The mercury species over Europe (MOE) project was aimed at identifying sources, occurrence and atmospheric behaviour of atmospheric Hg species. Within MOE, emission measurements, ambient air measurements, process and regional-scale modelling and laboratory measurements were conducted. In this work, a summary of some of the main results is given. From the emission measurements, information on stack gas concentrations and emission factors for five coal fired power plants and three waste incinerators are presented. Results from field measurements of mercury species in ambient air at five locations in Northern Europe are presented. Examples from regional-scale atmospheric modelling are also given. The results emphasise the importance of information on Hg species for instance in emission inventories and measurement data from background sites. Furthermore, the importance of considering the role of the global cycling of mercury in future control strategies is emphasised.

Distribution of TPM in Northern Europe

Total particulate mercury (TPM) in air has been measured during five 2-week campaigns at five measurement sites in Northern Europe. The measurements covered four seasons and the result constitutes a unique TPM data set from this region. Evidence for transport of TPM on a regional scale is reported as well as the historical trend of TPM in south of Sweden. All TPM measurements were made using a new mini particulate sampler. The device consists of a quartz fibre filter contained in a quarts glass filter holder and is a modified version of the MiniSamplr. This approach proves to be reliable and more cost efficient in comparison to alternative methods. Tests made to evaluate the performance of the sampler in terms of precision and comparability with sampling on Teflon membrane filters are also reported.

A description of an automatic continuous equilibrium system for the measurement of dissolved gaseous mercury

A novel continuous equilibrium system with high time resolution, i.e. every ten minutes, was developed to sample and determine dissolved gaseous mercury (DGM) in natural surface waters. The system is based on the opposite flow principle, can be connected to a ship’s bow water system, and can be applied under most ambient conditions, such as high wind speeds and onboard a moving ship. For the DGM determination the system uses the measured equilibrium concentration of mercury established between the aqueous and gaseous phases, i.e. DGM = Hgextr / kH′, where Hgextr is the measured mercury concentration in the outgoing gas phase and kH′ is the dimensionless Henry’s Law constant at the desired temperature and salinity. The efficiency of the system was investigated via theoretical calculations and by comparing the continuous equilibrium system with discrete samples. The measurements obtained by the continuous equilibrium system agree within 13% at the 95% confidence level with the measurements of discrete samples obtained by the traditional technique. The theoretical calculations estimated that the continuous equilibrium system described here had an efficiency of 99% for determining the DGM concentration.

Measurements of fractionated gaseous mercury concentrations over northwestern and central Europe, 1995-99

Although it makes up only a few per cent. of total gaseous mercury (TGM) in the atmosphere, the fraction of oxidised (divalent) mercury plays a major role in the biogeochemical cycle of mercury due to its high affinity for water and surfaces. Quantitative knowledge of this fraction present in mixing ratios in the parts-per-10(15) (ppq) range is currently very scarce. This work is based on approximately 220 data for divalent gaseous mercury (DGM) collected during 1995-99 in ambient air. Over the course of the measurements, the sampling and analytical methods were modified and improved. This is described here in detail and includes transition from wet leaching and reduction procedures to thermo-reductive desorption, the use of annular as well as tubular denuders and adoption of an automated sampling system. The concentration of DGM exhibited a strong seasonal behaviour in contrast to atomic gaseous mercury, with low values in winter and maximum values in summer. The DGM/TGM ratios were frequently found to be below the detection limit (< or = 1%) and in the range 1-5%. A trend of diurnal DGM patterns was observed and implies photolytically induced sources. Scavenging of DGM during rain events was also noticed.