REGIONAL BUDGETS OF SOME HEAVY METALS IN EUROPE

Ilia Ilyin*(Meteorological Synthesizing Centre -East, Kedrova str. 8-1, Moscow, Russia. Tel: 007 095 124 47 58, Fax: 007 095 310 70 93, e-mail: msce@glasnet.ru)

ABSTRACT

Regional-scale atmospheric budgets of heavy metals (Pb, Cd, and Hg) were calculated for European territory by a numerical model developed in the framework of the Convention on Long-Range Transboundary Air Pollution (CLRTAP). The comparison of model results against measurements indicated agreement within a factor of 2. Comparison of regional budget items indicates that Europe is a net importer of Pb, Cd, and Hg. In general, a relative contribution of direct anthropogenic emissions to depositions on individual countries is greater for Pb and Cd and less for Hg in comparison with natural and transboundary sources.

Introduction

Problems concerning long-range transport of heavy metals (HM) have been investigated for the last three decades. New impulse to pay much attention to this problem was given by the International Protocol on Heavy Metals signed in the framework of the Convention on Long-Range Transboundary Air Pollution (CLRTAP). Meteorological Synthesising Centre-East (MSC-E), being one of three centres of European Monitoring and Evaluation Programme (EMEP) is responsible for modelling of HM transport and deposition in the framework of the Convention. According to the Protocol, metals of the first priority are lead, cadmium and mercury. The purpose of this work is to evaluate regional budget of HMs for Europe, and to reveal the contribution of European countries to deposition on each other using numerical operational model developed in MSC-E. The results presented in this work refer to 1996.

Model description

Calculations of HM transport and deposition are carried out using a multi-layer Eulerian-type flat-terrain model on the grid in the stereographic projection with 50-km spatial resolution at 60° latitude. Model domain covers Europe, Northern Atlantic, Northern Africa, Middle Asia and partly Greenland. Along the vertical the model domain extends up to about 4 km, and separated in 5 non-uniform layers. Detailed description of the model used in calculations one can find in [Pekar, 1996, Ryaboshapko et al., 1998, 1999].

In this work anthropogenic and natural emissions of lead, cadmium and mercury are considered. For mercury the third input – re-emission is also taken into account. Re-emission is treated as a secondary input of previously deposited anthropogenic mercury. Detailed description of emission data sets used in calculations one can find in [Ryaboshapko et al, 1999].

Atmospheric transport in the horizontal and vertical direction is calculated using the scheme developed by M. Pekar [1996]. The scheme is stable, conservative, and positively defined.

Mercury transformation scheme used in the model is based on mercury chemical module developed by G. Petersen et al. [1998]. The module was adapted and simplified so that analytical solution is given [Ryaboshapko et al, 1999].

Parameterisation of dry deposition of particulate compounds is based on empirical model of G. Sehmel [1980] from which analytical formulae for dry deposition velocity, friction velocity, underling surface type and roughness length were derived [Pekar, 1996]. Dry deposition of Hg⁰ is described in this study in terms of dry deposition velocity, which depends on a season and the underlying surface type. Dry deposition velocity of Hg²⁺_gas is assumed to be 0.5 cm/s not depending on a season and the underlying surface. DMM is believed to have zero dry deposition velocity.

Washout of particulate substances (Pb, Cd, Hg²⁺_part) is described as first-order process. In this work seasonal dependence of the washout ratio for Cd- and Pb associated with particles was introduced [Ryaboshapko et al., 1999]. Washout ratio for Hg²⁺_part was taken equal to 5´10⁵ [Petersen et al. 1995]. Following G.Petersen et al [1995], washout ratio for Hg²⁺_gas is taken equal to 1.4´10⁶. Wet scavenging of elemental mercury occurs due to dissolution in the liquid phase of clouds according to the chemical scheme. As DMM is nearly insoluble, its wet removal is not considered.

The lateral and top boundaries of the model domain are open for the exchange with ambient air masses. Values of HM’s boundary concentrations were taken different for different parts of the boundaries [Ryaboshapko et al, 1999].

Comparison with measurements

Calculated mean annual concentrations in the air and precipitation were compared against measurement data collected at the EMEP monitoring network and described in [Ryaboshapko et al., 1999]. All monitoring data used in the comparison refer to 1996. The comparison results for lead are shown in Figure 1.

Figure 1: Comparison of lead concentrations in air (a) and in precipitation (b).

As seen from the figure 1a, the difference between measured and modelled concentrations in the air lay within a factor of 2 for most of monitoring sites. However, the calculated concentrations in precipitation are somewhat underestimated (see figure 1b). On the average, measured concentrations in precipitation are 1.6 time higher than modelled ones. Comparison results for cadmium are similar to those for lead. Difference between modelled and measured values of total gaseous mercury (TGM) concentrations does not exceed 30%. Measured and modelled concentrations in precipitation lay within the factor of 2, the highest difference is observed for German sites.

European atmospheric budget for the HMs

Table 1 demonstrates regional budget of the three considered metals for the model domain. About 8,000 tonnes of lead, 40 tonnes of cadmium and 120 tonnes of mercury leave the model domain annually, testifying that Europe is a net importer of HMs in the atmosphere of the globe. High amounts of mercury transported in and out of the domain are explained by relatively high background concentrations, represented mainly by long-living elemental form. Relatively uniform vertical distribution of mercury is also responsible for rather high upward and downward fluxes through the model top.

Table 1: Annual budget of the HMs, t/y

Budget item	Mercury forms					Pb	Cd
Budget item	Hg⁰	Hg⁺²_gas	Hg⁺²_part	DMM	SHg	Pb	Cd
Total emission	418	95	57	27	597	40520	770
· Natural	197	0	0	22	219	910	50
· Direct anthropogenic	174	95	57	0	326	39610	720
· Re-emission	45	0	0	5	50	0	0
Advective inflow	8559	0	60	0	8619	2370	120
Inflow through the top	9712	0	65	0	9777	40	2
Total deposition	148	88	262	0	498	32600	740
· Dry deposition	129	29	17	0	175	4790	120
· Wet deposition	18	60	245	0	323	27810	620
Advective outflow	9101	4	177	1	9283	5600	90
Outflow through the top	9082	3	157	0	9242	4830	70

Source-receptor relationships

The model is capable of calculating depositions from every country to the receptor of interest such as another country, lake, sea etc. Table 2 exemplifies three greatest “importers” of lead to some European countries. The table also includes contribution from own sources (COS) and input of natural and global anthropogenic sources (NAT). The full budget matrix for the considered HMs for 1996 can be found in [Ryaboshapko et al., 1999].

Table 2: Major countries-emitters and their contribution to depositions of lead to countries-receivers, %

Receiver	Major countries-sources (input in %)						COS, %	NAT, %
Austria	France	10	Czech Rep.	8	Italy	8	24	4
Czech Rep.	Poland	12	Germany	8	France	4	54	2
Denmark	U.K.	15	Germany	13	France	12	22	3
France	Spain	8	U.K.	3	Belgium	3	77	2
Germany	France	17	U.K.	5	Belgium	5	51	3
Norway	U.K.	26	France	12	Russia	11	4	10
Poland	Ukraine	9	Czech Rep.	9	Germany	4	56	2
Iceland	U.K.	27	France	14	Germany	5	6	28
U.K.	France	7	Belgium	2	Germany	1	82	2

As seen from the table, for many countries the natural input is not high. Similar results were obtained for cadmium. Contribution from the own sources is usually high for countries with high emissions, whereas countries with low emission (e. g., Norway), are basically influenced by their neighbours. For some countries, for example, Iceland, the natural input can amounts to several tens of per cent. In the case of mercury total contribution from natural, global anthropogenic sources and re-emission is much greater and can exceed 80% for certain countries [Ryaboshapko et al., 1999]. This fact implies that mercury is a global-scale pollutant and global and hemispherical models are needed to describe its transport on a scale larger than regional one.

Conclusions

The model presented includes basic processes responsible for fate of the HMs in the atmosphere. The model simulates concentrations and depositions of lead, cadmium and mercury on the regional scale and the calculated results agree with measurements within a factor of 2. Items of European regional HM budget were evaluated. Analysis of calculated budget items shows that Europe is a net importer of the HMs to the global atmosphere. Contributions of individual countries to depositions on European regions were exemplified.

References

Pekar M. (1996). Regional models LPMOD and ASIMD. Algorithms, parametrization and results of application to Pb and Cd in Europe scale for 1990. MSC-E/EMEP, Technical Report 9/96.

Petersen G., Munthe J., Pleijel K., Bloxam R., & Kumar A.V. (1998) Atmospheric Environment, Vol. 32, No. 5, pp. 829-843.

Petersen G., Iverfeldt A. & Munthe J. (1995) Atmospheric Environment, Vol. 29, pp. 47-67.

Ryaboshapko A., Ilyin I., Gusev A., & Afinogenova O., Berg T., A. Hjellbrekke. (1999) Monitoring and Modelling of Lead, Cadmium and Mercury Transboundary Transport in the Atmosphere of Europe. Meteorological Synthesizing Centre - East, EMEP/MSC-E Report 1/99, 1999, Moscow, 123 p.

Ryaboshapko A., Ilyin I., Gusev A., & Afinogenova O. (1998) Mercury in the Atmosphere of Europe: Concentrations, deposition patterns, transboundary fluxes. Meteorological Synthesizing Centre - East, EMEP/MSC-E Report 7/98, June 1998, Moscow, 55 p.