A modelling method for estimating transboundary air pollution in southeastern Europe

Transcription

1 Environmental Modelling & Software 19 (2004) A modelling method for estimating transboundary air pollution in southeastern Europe N. Moussiopoulos a,, C.G. Helmis b, H.A. Flocas b, P. Louka a,b, V.D. Assimakopoulos b, C. Naneris a, P. Sahm a a Laboratory of Heat Transfer and Environmental Engineering, Aristotle University Thessaloniki, Box 483, Thessaloniki, Greece b Physics Department, Section of Applied Physics, National and Kapodistrian University, Athens, Greece Received 5 February 2003; received in revised form 16 May 2003; accepted 24 July 2003 Abstract A new methodology is presented for the model estimation of an import export pollution balance across country borders based on the classification of the synoptic scale atmospheric circulation. As an application, the transboundary transport of SO 2 and NO x across the Greek borders is investigated for the year The annual total inflow outflow fluxes were derived by weighting the model results with the annual relative frequency of the corresponding synoptic type appearance. The results of the new modelling method are similar to those following the day-by-day calculation of the inflow outflow fluxes for the whole year 1995 using the same models. The advantage of the new methodology is that it is definitely less time-consuming than the day-by-day calculations. Hence, the proposed methodology can be employed as a practical tool for several applications requiring the implementation of complex models over longer time periods Elsevier Ltd. All rights reserved. Keywords: Synoptic classification; Transboundary air pollutant transport; Air pollution budget 1. Introduction Long-range transport of air pollutants is one of the main issues that European Union includes in its legislation. In particular, transboundary air pollution, i.e. the air pollution generated in one country and being transported to its neighbouring countries is considered as a major European problem. A recent assessment of the transboundary air pollution in the European Union (EEA, 1999) revealed that major emissions reductions for SO 2 and NO x as adopted under the Convention on Long Range Transboundary Air Pollution (CLRTAP) and EU legislation, primarily the Directive 2001/81/EC on National Emission Ceilings, have reduced the harmful effects associated with the presence of these substances, namely their contribution to the formation of photochemical smog and the acidification and eutrophication of Corresponding author. Tel.: ; fax: address: moussio@eng.auth.gr (N. Moussiopoulos). water and soil. The multiple role, however, of SO 2 and NO x causes interconnection between environmental problems that does not allow a complete address of the impacts of the transboundary air pollution. The spatial distribution of SO 2 and NO x is influenced by both the emission pattern and the meteorological conditions. More specifically, SO 2 efficiently deposits close to the emission source, whereas the area of influence of NO x is found to be considerably larger due to its lower depletion rate. The residence time and distances of transport have been shown to vary geographically with transport distances, increasing from Central Europe outwards (Barrett et al., 1995). The meteorological conditions determine the transport distances and the dry deposition of emitted species through the wind field, the aerodynamic resistance in the boundary layer and the mass exchange with the free atmosphere, depending on the vertical wind component (Chung, 1978; Cheng and Angle, 1996; Klaic, 1996). Mesoscale and regional scale computational models are often applied in predicting long-range air pollution diffusion and transport from different areas based on /$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi: /j.envsoft

2 550 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) existing data on the prevailing mesoscale and synoptic scale circulations, as well as taking into account the emission inventories developed for the different sources of pollutants in each region. Such complex air pollution models (e.g. EMEP) are heavy regarding their CPU time costing to be applied on a day-by-day basis for longer time periods (e.g. a whole year). Hence, a new modelling method is required for treating such cases that will further offer a practical tool for several applications related with the new EU air quality legislation requirements for the knowledge of yearly air pollution statistics, e.g. activities developing under the Clean Air For Europe (CAFE) programme. In the present paper, a new method is proposed in compliance with the above requirements. Specifically, the aims of the present research work are to develop and test a new methodology for the model estimation of an import export pollution balance across country borders, based on the classification of the synoptic scale atmospheric circulation; and to assess the results produced with this method versus conventional day-by-day calculations. As an application of this method, the transboundary transport of SO 2 and NO x across the Greek borders is investigated for a typical year. 2. Model setup Model simulations were performed with the coupled non-hydrostatic mesoscale model MEMO and the Eulerian dispersion model TRAPPA. The simulation domain (cf. Fig. 1) covers an area of km 2 at a spatial resolution of 50 km. This area includes practically the whole of the Balkan peninsula and parts of Italy and Turkey. Simulations with TRAPPA were performed for three scenarios: The first one takes into account emissions of SO 2 and NO x in the whole of the above domain, the second scenario ignores emissions outside the Greek borders. A third scenario excluding the Greek emissions from the domain totals may be derived in a trivial manner from the model results for the first two. Transboundary transport of air pollutants between Greece and the other Balkan States and Turkey were calculated in terms of accumulated lateral inflow outflow fluxes up to a height of 5000 m above sea level through the side-walls of a balancing box covering an area of km 2 indicated as a frame in Fig. 1. It should be noted that the height of 5000 m is considered sufficient for calculations concerning transport of air pollutants in the horizontal scale of 1500 km of our study. The modelling approach was adopted for 1995 since there was a complete emission inventory available for this year. The coupled MEMO-TRAPPA modelling system was applied for both the day-by-day analysis and the new methodology. It should be emphasised here that, as the main focus of the paper is to illustrate the advantages Fig. 1. Simulation domain of the model MEMO. The frame corresponds to the domain of the balancing box for the calculations of the transboundary fluxes with the aid of TRAPPA model. of the new methodology compared to the conventional analysis, the calculation of SO 2 and NO x considered both pollutants as inert, an assumption that does not greatly affect the extraction of the conclusions. Nevertheless, further support to the quantitative results obtained with the modelling system is provided with their direct comparison against the corresponding EMEP results as discussed in the next sections Model description The non-hydrostatic mesoscale model MEMO (Moussiopoulos et al., 1993; Kunz and Moussiopoulos, 1995; Moussiopoulos, 1995) has been developed at the Aristotle University Thessaloniki in collaboration with the University of Karlsruhe. MEMO is a prognostic model in the local-to-regional scale, which allows the air motion over a complex terrain to be described. The code also allows multiple nesting. Within MEMO, the conservation equations for mass and momentum, including the volumetric Coriolis force components (Kunz and Moussiopoulos, 1995), and scalar quantities as potential temperature, turbulent kinetic energy and specific humidity are solved in terrain-influenced co-ordinates. For the calculation of inert pollutant dispersion, a specially adjusted Eulerian dispersion model, TRAPPA, was applied. TRAPPA allows describing of the dispersion of inert pollutants over complex terrain. To preserve conservativity, the finite volume approach is employed in the model. By a non-equidistant grid level distribution

3 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) in the vertical direction a better resolution near the ground is achieved and for a better formulation of boundary conditions at the lower boundary, the model TRAPPA uses the transformation to terrain-following coordinates adopted in the MEMO model. Advective terms are treated with the Flux Corrected Transport Adams-Bashforth scheme (Wortmann-Vierthaler and Moussiopoulos, 1995). Vertical turbulent diffusion is treated using the second-order Crank Nicolson method and the dry deposition process is described with the bigleaf multiple resistance model concept (Sahm, 1997). More details on TRAPPA are to be found elsewhere (Moussiopoulos, 1995; Moussiopoulos et al., 1997) Model input data The initial and boundary meteorological conditions were formulated with the aid of data of wind speed and direction and temperature at approximately 700 m above ground level for the period 1 January to 31 December 1995 at a spatial resolution of 150 km and a temporal resolution of 6 h. This data set was made available from the Norwegian Meteorological Institute s numerical weather prediction model (NWP), which is described in detail in Grønas and Hellevik (1982), Grønas and Mitbo (1986) and Nordeng (1986). The initial and boundary concentrations of SO 2 and NO x were derived from regional background concentrations of the EMEP model for the period 1 January to 31 December 1995, at a spatial resolution of 150 km and a temporal resolution of 6 h (Simpson, 1995). The EMEP model results were interpolated horizontally on the study domain based on a modified quadratic Shepard method developed by Renka (1988). As no information on the vertical distribution was available, the concentrations were assumed constant with height. Between two subsequent data sets the concentrations were interpolated linearly in time. Both area and elevated emissions were based on yearly total emissions of SO 2 and NO x for the year 1995 with a spatial resolution of 50 km, which were supplied by the Norwegian Meteorological Institute. The emissions were interpolated spatially again using the modified quadratic Shepard method. Based on this emission inventory, the highest surface SO 2 emissions are confined in Bulgaria, Bosnia-Herzegovina and Serbia, while elevated NO x emissions are mainly found over Greece, Bulgaria and Turkey (not shown). 3. Day-by-day simulations Simulations with the non-hydrostatic mesoscale model MEMO and the Eulerian dispersion model TRAPPA were performed for each day of the year Both models were applied for consecutive periods of 8 days each throughout the whole of the year, the first day of each period considered for initialisation. Simulations with TRAPPA were performed for the three scenarios mentioned in Section 2. According to MEMO results, highest inflow density through the boundary close to the ground is predicted in the west over Albania and parts of the Ionian Sea, in the north over the Rila mountains and in the south over Crete. Highest inflow at upper levels is predicted in the south-east over the Dodecanese Islands. In Table 1 the total mass balance of the balancing area (cf. Fig. 1) is shown, estimated for the 1-year period for the three emission scenarios considered. More specifically, this table lists the accumulated lateral inflow and outflow of the two species considered, as well as the accumulated deposition and emissions within the balancing area. It should be noted that the fluxes are calculated up to 5000 m above sea level. According to this figure, Table 1 reveals that with regard to SO 2, Greek emissions are small fractions compared to the total fluxes passing the balancing area. The fraction of Greek NO x emissions contributing to the total outflow, however, is considerable. About half of the SO 2 and about 40% of the NO x emitted in Greece are deposited locally. The table further reveals that about 25% of total deposition of SO 2 and about 30% of the total deposition of NO x originate from Greece s own emissions. The remainder, about 75% of the SO 2 and 70% of the NO x deposited are imported. Although TRAPPA simulated NO x and SO 2 as inert pollutants, comparison of the above values with those reported in EMEP/MSC-W Transboundary Programme (EMEP/MSC-W, 1998) reveals that the results of the coupled MEMO-TRAPPA modelling system are consistent with the corresponding results of EMEP. In particular, according to EMEP/MSC-W 77% SO 2 and 78% NO x deposited in Greece were imported in 1995 values being similar to those obtained with MEMO-TRAPPA. This similarity implies that the modelling system applied in the present work may be capable in providing quantitative results for the transboundary transfer of the pollutants treated here, namely NO x and SO 2. In addition, according to the simulation results (not shown here), imported depositions were high, as much as 95% (of the total deposition), near the surrounding boundary area, especially near the northeast and southwest borders, whereas a relatively low contribution of imported pollutants to the total deposition was estimated at the domain centre (about 25%). Figs. 2 and 3 present, respectively, the inflow and outflow flux density within the lower 2000 m above sea level integrated over the year It can be seen that for SO 2 the inflow is substantially larger from the north, being maximised over the mountain of Rodopi, near the border with Bulgaria. On the other hand, SO 2 prefers to exit northwards. For NO x,inflow mainly exists again from the north northeast and mainly from Bulgaria. The

4 552 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) Table 1 Total fluxes through the balancing box and total deposition and emission as calculated by the TRAPPA model for the period 1 January to 31 December 1995 (units: kt) Lateral inflow Lateral outflow Deposition Emission All emissions SO NO x Emissions only in Greece SO NO x No emissions in Greece SO NO x Fig. 2. Inflow flux density of NO x and SO 2 through the balancing box within the lower 2000 m above sea level as estimated by the day-by-day simulations, integrated over the year 1995 (units: g/m 2 ). The four frames correspond to the four faces of the balancing box volume. In each frame, the contour of the mountains at the intersection with the corresponding face of the balancing box volume is also drawn. outflow is not as significant as for SO 2, with larger values being confined near the ground towards the northwest. It is of interest to note that the SO 2 inflow flux from southeast increases substantially with height (see Fig. 2), more likely suggesting the long distance transport of the pollutant from this direction. In Table 2 the accumulated lateral inflow and outflow of the two species split into the four faces of the balancing box are summarised up to 5000 m above sea level. From Table 2 it becomes evident that the inflow masses being derived when Greece is excluded from the balancing box slightly differ from the corresponding masses when the whole examined area is considered, and consequently the Greek emissions of SO 2 and NO x are only small fractions of the total import fluxes passing the balancing area. Nevertheless, the overall contribution of the Greek emissions to the total outflow, especially of NO x, seems to be more important, because the emissions of the large power units in western Macedonia and greater Athens area are found to be considerable. 4. Application of the new methodology The synoptic scale atmospheric circulation over Greece was typified on a daily basis, employing an automatic classification scheme at the isobaric level of 850 hpa, as described by Helmis et al. (2003) for the typi-

5 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) Fig. 3. As in Fig. 2, but for the outflow flux density. Table 2 Total inflow and outflow through the balancing box as calculated by the TRAPPA model for the period 1 January to 31 December 1995 (units: kt) North West South East Total Inflow All emissions SO NO x Emissions only in Greece SO NO x No emissions in Greece SO NO x Outflow All emissions SO NO x Emissions only in Greece SO NO x No emissions in Greece SO NO x cal from a climatological point of view year Six anticyclonic and eight cyclonic types of circulation that predominate over Greece are distinguished. Table 3 presents the mean relative frequency of appearance of the synoptic types for 1995, which does not differ from the corresponding climatological value for a 40 years ( ) period, except of the relatively higher frequency of the type A5. According to Helmis et al. (2003), the selection of the representative days was justified from both a statistical and a meteorological point of view, considering the frequency distribution of each synoptic type throughout 1995, along with the corresponding intra-annual variations. More specifically, the following criteria were adopted: (a) a representative day of cyclonic type appears during the month that the frequency of the corresponding type is maximised; (b) two different days represent each of the six anticyclonic types to allow for seasonal differences: the first maximum frequency appears in the cold period (November to April) and the

6 554 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) Table 3 Synoptic types used for the classification scheme along with their relative frequency (%) of appearance for 1995 Type Relative frequency (%) A1 5.2 A2 4.7 A A A A6 1.1 C 15.3 Cs 5.2 Csw 8.8 Cnw 4.9 Cne 9 Cse 0.8 Cn 3 Cw 1.4 second in the warm period (May to October); (c) the previous and following days of the representative day are also characterised by the same type, in a way that time continuity is qualified; (d) if more than one type appear their maximum frequency in the same month, then the secondary maxima of the types are considered, in a way that the representative days do not concentrate in a small number of months, but rather expand, as possible, throughout the whole year. Following the proposed selection criteria, 20 days were selected during 1995, representing each of the eight cyclonic types and each of the six anticyclonic types, while each anticyclonic type is represented by 2 different days, one during the warm and the other during the cold period of the year. Then, the annual import export balance between Greece and the neighboring countries was calculated, by weighting the inflow and outflow fluxes on each day with the annual relative frequency of appearance of the corresponding type during It should be noted that, since the estimation of annual inflow outflow budget, with the aid of the proposed methodology, is solely based on calculations of representative days, Helmis et al. (2003) investigated the sensitivity of the estimation on the selection of different set of days. More specifically, the import export fluxes were calculated as above, however, with different sets of representative days and then they were compared with the corresponding annual values derived on a daily basis, which are considered to be the reference values. According to their results, there are only minor differences in the values of the total inflow and outflow values, when all four selection criteria are fulfilled, thus suggesting that the representativeness of the selected days in the proposed methodology is well justified. Table 4 shows the total pollutant masses at inflow and outflow through the balancing box as calculated by the annual (year 1995) relative frequencies for each type circulation at 850 hpa, for the three emission scenarios considered up to the height of 5000 m above sea level. Comparing Tables 2 and 4 and considering the relative differences (%) of the results being derived employing the new methodology minus those derived following the day-by-day calculations, multiplied by the latter results, it can be seen that the new approach leads to rather small relative differences (order of 10 15%) for the total inflow and outflow values. In the values corresponding to the four components, an overestimation becomes evident using the new methodology as compared to the dayby-day calculations, except for the northerly component of the inflow and the westward component of the outflow where the new method leads to an underestimation. The inflow and outflow flux density within the lower 2000 m above sea level for each of the four faces of the bal- Table 4 Total inflow and outflow through the balancing box as calculated by the annual (year 1995) relative frequencies for each type circulation at 850 hpa (units: kt) North West South East Total Inflow All emissions SO NO x Emissions only in Greece SO NO x No emissions in Greece SO NO x Outflow All emissions SO NO x Emissions only in Greece SO NO x No emissions in Greece SO NO x

7 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) ancing box volume, as derived from the new estimation method (not shown) does not reveal any remarkable change as compared to the day-by-day estimation. In order to investigate the model results with respect to the different meteorological conditions, full analysis will be presented for two case studies, one anticyclonic (A1) and one cyclonic (Cw), that are characterised by remarkable transportation of pollutant air masses from different directions. It should be noted that the relative frequency of appearance of Cw and A1 during 1995 is 1.4% and 5.2%, respectively (see Table 3) Type Cw (10/2/95) Fig. 4a presents the simulated wind field at the isobaric level of 850 hpa over the Greek area (see Fig. 1) for 10/2/95 at 12:00 LST. It can be seen that the wind prevails principally from northwest over the western part and from southwest over the eastern part, that strengthens over northern Greece. Figs. 5 and 6 display the inflow and outflow flux density of SO 2 and NO x within the lower 2000 m above sea level through the balancing box, as calculated by the TRAPPA model from 00:00 LST on 10/2/95 to 00:00 LST on 11/2/95. The total inflow for both pollutants is particularly increased, and specially the NO x inflow that attains the highest value as compared to the other weather types studied (not shown). The importing SO 2 primarily originates from the west and north northeast (Fig. 5), consistent with the prevailing wind field. Similarly, NO x originates from north-northwest. The outflow for SO 2 directs mainly eastwards (Fig. 6) and for NO x southeastwards with a substantial contribution of the Greek emissions. It is noteworthy that the maximum exported NO x is observed under this synoptic type Type A1 (9/10/95) Intense northeasterlies prevail over the major part of the examined area, with higher intensity over the Aegean sea (Fig. 4b). The importing SO 2 comes mostly from the north, with particularly large fluxes in the eastern side of Rodopi mountain (Fig. 7). NO x prefers to enter from the north as well, with however, a significant easterly component. In this case, the outflow for both pollutants directs southwestwards (Fig. 8). It should be noted that the flux of the exported NO x is especially large under this synoptic type compared to the other types studied. The inflow outflow pattern seems to be consistent with the direction and intensity of the predominant background flow. Fig. 4. Wind field at 850 hpa as derived from MEMO: (a) in 10/2/95, at 12:00UTC; and (b) in 9/10/95 at 0400 LST over the area that is included in the frame of Fig Conclusions The non-hydrostatic mesoscale model MEMO and the Eulerian dispersion model TRAPPA have been applied for studying the transboundary air pollutant transport to and from Greece for a 1-year period (1995). Transboundary pollutant fluxes across country borders were calculated on an annual basis employing two methods:

8 556 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) Fig. 5. Inflow flux density of NO x and SO 2 through the balancing box within the lower 2000 m above sea level as calculated from 00:00 LST, to 00:00 LST, (case Cw). Fig. 6. As in Fig. 5, but for outflow flux density.

9 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) Fig. 7. Inflow flux density of NO x and SO 2 through the balancing box within the lower 2000 m above sea level as calculated from 00:00 LST, to 00:00 LST, (case A1). Fig. 8. As in Fig. 7, but for outflow flux density.

10 558 N. Moussiopoulos et al. / Environmental Modelling & Software 19 (2004) (i) a conventional method, using the results for each day of the year, and (ii) a new method, using results of 20 selected days during the year, being considered as representative of different synoptic types with corresponding frequency of appearance. It was demonstrated that both methods provide similar results regarding pollutant inflow and outflow, as well as local deposition in Greece. The advantage of the new methodology is that less time is evidently consumed as compared to the day-byday methodology. The results of the present paper confirm that, under specific conditions, yearly air pollution statistics may be obtained with complex models applied over a limited time period. Therefore, the proposed methodology can be employed as a practical tool for several applications requiring the implementation of complex models over longer periods. This option may gain considerable practical significance, as EU air quality legislation in most cases requires the knowledge of yearly statistics. Moreover, as atmospheric pollution dispersion in the lower atmosphere is often categorised according to the synoptic weather types, this procedure appears feasible for assessing air quality limit value exceedance in conurbations. Acknowledgements This work was supported by the Hellenic Ministry of the Environment, Physical Planning and Public Works as part of the project Undertaking of international obligations of Greece in the frame of the protocol conventions for the transboundary atmospheric pollution at long distances and the development of control infrastructure coordinated by Prof. C. Helmis, National and Kapodistrian University of Athens. References Barrett, K., Seland, O., Foss, A., Mylona, S., Sandnes, H., Styve, H., Tarrason, L., European Transboundary Acidifying Air Pollution. Ten years calculated fields and budgets to the end of the first Sulphur Protocol. In: EMEP MSC-W Report 1/95, Research Report No. 17. Norwegian Meteorological Institute, Oslo, Norway. Cheng, L., Angle, R.P., Model calculated interannual variability of concentration, deposition and transboundary transport of anthropogenetic sulphur and nitrogen in Alberta. Atmos Environ 30, Chung, Y.S., The distribution of atmospheric sulphates in Canada and its relationship to long range transport of air pollutants. Atmos Environ 12, EMEP/MSC-W. (1998). Transboundary acidifying air pollution in Europe. Part 2: Numerical addendum, EMEP MSC-W Status Report 1/98, Research Report No. 66, Norwegian Meteorological Institute, Oslo, Norway. European Environment Agency (1999). Environment in the European Union at the turn of the century. Environmental Assessment Report, No. 2, 446 pp. Grønas, S., Hellevik, O. (1982). A limited area prediction model at the Norwegian Meteorological Institute. Norwegian Meteorological Institute Technical Report No. 61. Grønas, S., Mitbø, K.H. (1986). Four dimensional data assimilation at the Norwegian Meteorological Institute. Norwegian Meteorological Institute Technical Report No. 66. Helmis, C.G., Moussiopoulos, N., Flocas, H.A., Sahm, P., Assimakopoulos, V.D., Naneris, C., Maheras, P., Estimation of transboundary air pollution on the basis of synoptic scale weather types. Int J Climatol 23, Klaic, Z., A Lagrangian model of long-range transport of sulphur with the diurnal variations of some model parameters. J Appl Meteor 35, Kunz, R., Moussiopoulos, N., Simulation of the wind field in Athens using refined boundary conditions. Atmos Environ 29, Moussiopoulos, N., Flassak, T., Berlowitz, D., Sahm, P., Simulations of the wind field in Athens with the nonhydrostatic mesoscale model MEMO. Environ Software 8, Moussiopoulos, N., The EUMAC Zooming Model, a tool for local-to-regional air quality studies. Meteorol Atmos Phys 57, Moussiopoulos, N., Sahm, P., Karatzas, K., Papalexiou, S., Karagiannidis, A., Assessing the impact of the new Athens airport to urban air quality with contemporary air pollution models. Atmos Environ 31, Nordeng, T.E. (1986). Parameterization of physical processes in a three-dimensional numerical weather prediction model. Norwegian Meteorological Institute Technical Report No. 65. Renka, J.R., ALGORITHM 661: QSHEP3D: quadratic Shepard method for trivariate interpolation of scattered data. ACM Transactions on Mathematical Software 14 (2), Sahm, P., Kopplung eines nicht-hydrostatischen prognostischen Grenzchichtmodells und eines mesoskaligen Ausbreitungsmodells fur reaktive Stoffe. Fortschr-Ber VDI, Reine 15 (199), 170. Simpson, D., Biogenic emissions in Europe 2: Implications for ozone control strategies. J Geophys Res 100 D11, Wortmann-Vierthaler, M., Moussiopoulos, N., Numerical tests of a refined flux corrected transport advection scheme. Environ Software 10,