Atmospheric Environment (v.35, #17)

Preface by Nicola Pirrone; Jozef M. Pacyna; Hartmut Barth (2977).

European emissions of atmospheric mercury from anthropogenic sources in 1995 by E.G. Pacyna; J.M. Pacyna; N. Pirrone (2987-2996).
Estimates of atmospheric emissions of mercury from anthropogenic sources in Europe in 1995 are presented with the information on emissions of both total mercury and its major chemical and physical forms. The 1995 anthropogenic emissions of total emissions were estimated to be about 342  tonnes , a decrease of 45% compared to these emissions in 1990. Combustion of fuels, particularly coal has been the major source of anthropogenic emissions contributing to more than half to the total emissions. The emissions from coal combustion have not changed significantly over the past decade. Major decrease has been estimated for emissions from industrial processes, particularly the chlor-alkali production using the Hg cell process. In 1995 the European emissions of anthropogenic mercury contributed about 13% to the global emissions of this element from anthropogenic sources. The anthropogenic Hg emissions in Europe were still higher than the natural emissions in the region, estimated to be about 250–300  tonnes per year. The accuracy of estimates of anthropogenic emissions of Hg in Europe in 1995 is considered to be between 25 and 50%. The most accurate seem to be the estimates for combustion sources, while the most incomplete data were collected and/or estimated for waste disposal. The emissions of gaseous elemental mercury contributed about 61% to the emissions of the total mercury, while the contribution of gaseous bivalent mercury and particulate mercury was 32 and 7%, respectively.
Keywords: Atmospheric emission; Anthropogenic sources; Mercury and its species;

This report discusses past, current and projected mercury emissions to the atmosphere from major industrial sources, and presents a first assessment of the contribution to the regional mercury budget from selected natural sources. Emissions (1995 estimates) from fossil fuels combustion (29.8  t yr −1), cement production (28.8  t yr −1) and incineration of solid wastes (27.6  t yr −1), all together account for about 82% of the regional anthropogenic total (105.7  t yr −1). Other industrial sources in the region are smelters (4.8  t yr −1), iron–steel plants (4.8  t yr −1) and other minor sources (chlor-alkali plants, crematoria, chemicals production) that have been considered together in the miscellaneous category (9.6  t yr −1). Regional emissions from anthropogenic sources increased at a rate of 3%  yr −1 from 1983 to 1995 and are projected to increase at a rate of 1.9%  yr −1 in the next 25 years, if no improvement in emission control policy occurs. On a country-by-country basis, France is the leading emitter country with 22.6  t yr −1 followed by Turkey (16.1  t yr −1), Italy (11.4  t yr −1), Spain (9.1  t yr −1), the former Yugoslavia 7.9 (t yr −1), Morocco (6.9  t yr −1), Bulgaria (6.8  t yr −1), Egypt (6.1  t yr −1), Syria (3.6  t yr −1), Libya (2.9  t yr −1), Tunisia (2.8  t yr −1) and Greece (2.7  t yr −1), whereas the remaining countries account for less than 7% of the regional total. The annual emission from natural sources is 110  t yr −1 , although this figure only includes the volatilisation of elemental mercury from surface waters and emissions from volcanoes, whereas the contribution due to the degassing of mercury from top soil and vegetation has not been included in this first assessment. Therefore, natural and anthropogenic sources in the Mediterranean region release annually about 215  t of mercury, which represents a significant contribution to the total mercury budget released in Europe and to the global atmosphere.
Keywords: Mediterranean sea region; Natural emission; Anthropogenic emission; Trend; Projection; Emission factors; Per-capita emission; Control efficiency;

Intercomparison of methods for sampling and analysis of atmospheric mercury species by J Munthe; I Wängberg; N Pirrone; Å Iverfeldt; R Ferrara; R Ebinghaus; X Feng; K Gårdfeldt; G Keeler; E Lanzillotta; S.E Lindberg; J Lu; Y Mamane; E Prestbo; S Schmolke; W.H Schroeder; J Sommar; F Sprovieri; R.K Stevens; W Stratton; G Tuncel; A Urba (3007-3017).
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.
Keywords: Mercury; Measurement; Atmosphere; Speciation;

Atmospheric mercury distribution in Northern Europe and in the Mediterranean region by I. Wängberg; J. Munthe; N. Pirrone; Å. Iverfeldt; E. Bahlman; P. Costa; R. Ebinghaus; X. Feng; R. Ferrara; K. Gårdfeldt; H. Kock; E. Lanzillotta; Y. Mamane; F. Mas; E. Melamed; Y. Osnat; E. Prestbo; J. Sommar; S. Schmolke; G. Spain; F. Sprovieri; G. Tuncel (3019-3025).
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.
Keywords: Mercury field measurement; Total gaseous mercury; Total particulate mercury; Reactive gaseous mercury; Atmosphere;

Total gaseous mercury exchange between air and water at river and sea surfaces in Swedish coastal regions by Katarina Gårdfeldt; Xinbin Feng; Jonas Sommar; Oliver Lindqvist (3027-3038).
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 +11  ng m −2   h −1 (varying from −2.5 to +88.9  ng 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 +8.84  ng m −2   h −1 with an average evasion of +0.61  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.
Keywords: Aquatic systems; Biogeochemical cycling; Deposition; Evasion; Flux chamber;

Oxidation of atomic mercury by hydroxyl radicals and photoinduced decomposition of methylmercury in the aqueous phase by Katarina Gårdfeldt; Jonas Sommar; Dan Strömberg; Xinbin Feng (3039-3047).
The rate constant for Hg 0+. OH, k Hg 0+. OH =(2.4±0.3)×109   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.
Keywords: Biogeochemical cycling; Flux; Photolysis; Redox reactions;

A kinetic study of the gas-phase reaction between the hydroxyl radical and atomic mercury by Jonas Sommar; Katarina Gårdfeldt; Dan Strömberg; Xinbin Feng (3049-3054).
The atom is the dominating species of mercury in the atmosphere. Its oxidation processes are of great interest since it is mainly oxidised mercury that undergoes deposition and thereby spreads into the ecosystems and becomes bioaccumulated. The kinetics of the gas-phase reaction between atomic mercury and hydroxyl radical has been determined at room temperature and atmospheric pressure of air by relative rate technique. OH radicals were produced by photolysis employing methyl nitrite. By using cyclohexane as the reference compound, the rate coefficient obtained was k(Hg 0+ · OH)=(8.7±2.8)×10−14   cm 3   s −1 leading to natural lifetimes of mercury at global mean conditions of 4–7 month due to this reaction.
Keywords: Rate coefficient; Oxidation; Atmosphere; Mercury; Tropospheric life-time;

Following a modelling investigation of the role of the ambient aerosol in the cycling—that is the transport, transformation and deposition—of mercury in the atmosphere, the precise part played by the sea salt component of the marine aerosol in the remote marine boundary layer has been studied using a combination of models to describe the photolytic, gas phase and aqueous phase and heterogeneous chemistry of the marine boundary layer, in conjunction with inter phase mass transport and mercury chemistry. The role of the ocean in the emission of elemental mercury is, as yet, not entirely understood, but certainly the speciation of mercury deposited to the ocean surface is important as regards its re-emission. Models of mercury chemistry to date have tended to focus on cloud chemistry, and with good reason, as precipitation accounts for a large part of the global mercury deposition pattern; however, the composition of the marine aerosol is entirely different from that of cloud or fog droplets and the modelling studies here show that it plays a more local role being partially responsible for the gas phase speciation of mercury. The role of photochemical processes is investigated and particular attention is paid to halogen chemistry, as the chloride ion has been shown previously to have a notable effect on the concentration of oxidised mercury associated with particles, or better, solution droplets. The role of the sea salt component of the marine aerosol in the production of gas phase oxidised mercury species is described qualitatively and quantitatively.
Keywords: Photochemistry; Mercury; Marine boundary layer; Chemistry; Halogen; Cycling;

A comprehensive Eulerian modelling framework for airborne mercury species: model development and applications in Europe by G. Petersen; R. Bloxam; S. Wong; J. Munthe; O. Krüger; S.R. Schmolke; A.Vinod Kumar (3063-3074).
A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) has been developed under the Canada–Germany Science & Technology Co-operation Agreement and applied within the European Union MArine Science and Technology–BAltic Sea SYstem Study (MAST-III-BASYS) and the Environment & Climate project Mercury Species over Europe (MOE), to study the regional transport and deposition fluxes of atmospheric mercury species. The model is able to simulate long-range transport of mercury over the entire depth of the troposphere with a basic time step of 1  h and incorporates current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. Model predicted concentration and deposition pattern of mercury species over Europe are presented and concentrations of total gaseous mercury in ambient air and total mercury in precipitation calculated by the model are compared with observed values from a BASYS monitoring network study in February/March 1998. Concentrations in air agree within a factor of about 2 with observed values, thus indicating that the model is capable of reproducing observations satisfactorily even on an hourly basis. Observed monthly average concentrations in precipitation at four monitoring stations at the Baltic Sea coast are reproduced by the model within a factor of 1.3 suggesting that the chemical scheme in the model is based on an adequate parameterisation of aqueous phase chemistry.
Keywords: Mercury species; Numerical modelling; Eulerian models; Atmospheric mercury chemistry; Mercury deposition;