The MAPPE Strategy for GIS-Based Fate and Transport Modeling of Chemicals

The MAPPE Strategy for GIS-Based Fate and Transport Modeling of Chemicals

<p> 1 1</p><p>1A GIS-based approach for modeling the fate and </p><p>2 transport of pollutants in Europe</p><p>3A.Pistocchi</p><p>4EC, DG JRC, IES, via E.Fermi, 1, 21020 Ispra (VA) Italy</p><p>[email protected] tel +390332785591 fax +390332785601.</p><p>6Abstract</p><p>7 This paper presents an approach to estimate chemical concentration in multiple</p><p>8environmental media (soil, water, and the atmosphere) with the sole use of basic</p><p>9geographical information system (GIS) operations, and particularly map algebra. This</p><p>10allows solving mass balance equations in a different way from the traditional methods</p><p>11involving numerical or analytical solution of systems of equations, producing maps of</p><p>12chemical fluxes and concentrations only through combinations of maps of emissions and</p><p>13environmental removal or transfer rates.</p><p>14 Benchmarking with the well-established EMEP MSCE-POP model shows that the</p><p>15method provides consistent results with this more detailed description. When available,</p><p>16experimental evidence equally supports the proposed method in relation to the more</p><p>17complex approaches. </p><p>18 Thanks to the use of GIS calculations, the results can be obtained with a spatial</p><p>19resolution limited only by input data; the use of map algebra warrants flexible</p><p>20modification of the model algorithms, for e.g. partitioning, degradation, and inter-media</p><p>21transfer. 1 2</p><p>1 The management of data directly in GIS, with no need for model input and output</p><p>2processing, stimulates the adoption of up-to-date representations of landscape and climate</p><p>3variables nowadays more and more frequently available from remote sensing acquisitions</p><p>4and sectoral studies. </p><p>5 The method is particularly suited for a preliminary assessment of the spatial</p><p>6distribution of chemicals especially under high uncertainty and when many chemicals</p><p>7and their synergy need to be investigated, prior to dipping into more specialized and</p><p>8computation-intensive numerical models. </p><p>9Introduction </p><p>10 In the last years, researchers have spent efforts in developing spatially distributed</p><p>11fate and transport models of chemicals, i.e. models allowing spatially explicit</p><p>12representations (maps) of contaminants from a given spatial distribution of sources [1, 2,</p><p>133, 4, 5, 6, 7, 13, 28], as well as model intercomparison exercises [14, 15, 47]. </p><p>14 Existing spatially explicit models provide a valuable analytical tool in order to</p><p>15understand the mechanics of pollution; yet they tend to be rather complex when spatial</p><p>16resolution increases, requiring high computation time that makes them impractical</p><p>17outside of specific specialized studies.</p><p>18 At the same time, increasingly detailed spatial data on environmental processes</p><p>19and chemical emissions are becoming available in formats easy to process using</p><p>20geographic information systems (GIS). In chemical fate and transport modeling, GIS has</p><p>21been used so far mainly as a pre- and post-processor, although many examples appeared</p><p>22in the literature of spatially explicit models able to capture the fundamental spatial</p><p>23patterns of phenomena with no use of complex numerical models, capitalizing on the 1 3</p><p>1built-in analytical capabilities of GIS [27, 8, 9, 10, 26, 44]. By expanding the concepts</p><p>2already used in such approaches, and in many other areas of environmental and earth</p><p>3sciences, we aim at demonstrating the use of GIS calculations for chemical fate and</p><p>4transport assessment, as initially suggested in [23] and [25]. </p><p>5Materials and methods</p><p>6Map-algebraic formulation of the fate and transport equations</p><p>7In this paper, we solve the mass balance equation directly in GIS in terms of map algebra</p><p>8(e.g. [29, 30] among many others – see Figure 1 for a general scheme of the calculation).</p><p>9This is a standard technique by which gridcell-based GIS software manipulate maps, by</p><p>10applying algebraic operations on a cell-by-cell basis. Using analysis capabilities built in</p><p>11GIS allows a very simple set up of calculations, with great flexibility in the choice of</p><p>12algorithms, and with a straightforward control on the calculation steps for error tracking.</p><p>13Moreover, model resolution is only limited by the availability of data with no need of</p><p>14complex processing of model input.</p><p>15In the paper, we will refer to soil, air and seawater compartments only. The case of inland</p><p>16waters can be treated in map-algebraic terms as discussed in a separate paper [43] and in</p><p>17[23]. For soils, during a period of constant E0 and Koverall a solution of the mass balance</p><p>18equation is:</p><p>E0 19M = M0 exp(K overallt)  (1  exp(K overallt)) (1) K overall</p><p>20Where M0 is an appropriate initial distribution of mass, and K overall is the overall removal</p><p>21rate, E0 is a map of chemical emissions to soil, while t is time. 1 4</p><p>1Equation (1) holds for cases where advection from the surrounding cells is negligible.</p><p>2Such is the case, for instance, of soil when lateral exchanges (e.g. re-deposition of</p><p>3contaminated sediments eroded upslope; re-infiltration of contaminated water from</p><p>4upstream; subsurface lateral fluxes) can be neglected. In such a case, E0 is the sum of</p><p>5local mass discharge and atmospheric deposition. </p><p>6Under steady state conditions, equation (1) becomes:</p><p>E 7M= 0 (1a). K overall</p><p>8Seawater can be treated in this way, assuming negligible lateral transport due to currents</p><p>9and dispersion (“water column approach”) as discussed in [22]. </p><p>10The atmospheric compartment is described with the ADEPT model approach [31]. The</p><p>11concentration of a generic, reactive chemical in the atmosphere within the mixed layer at</p><p>12a generic point (x,y) is computed as:</p><p> n</p><p>13Catmo   EiSRi (x, y)exp(KΤti (x, y)) (2) i 1</p><p>14where Ei for i = 1, …, n is the emission at any of the n locations from where advective-</p><p>15dispersive fluxes enter the control volume. The maps SRi and Tti respectively represent a</p><p>16“source-receptor term” accounting for dilution and advective transport, and a “time of</p><p>17travel” of the contaminants, and K is the overall decay rate to which a chemical in subject</p><p>18throughout the pathway from the generic location i-th and the control volume boundary.</p><p>19As in the atmosphere advection and dilution largely dominate over other processes, a</p><p>20single K value for the whole Europe is normally acceptable [38]. The SRi and Tt maps</p><p>21used in this paper represent concentration in Europe (ug/m3) deriving from the emission</p><p>22of 1 Mt/y of a conservative contaminant in the generic i-th country, assuming emissions 1 5</p><p>1are distributed within the country according to population density. The ADEPT model</p><p>2(2) is evaluated and extended to a generic distribution of sources in a separate paper [21].</p><p>3 Atmospheric deposition is the product of a concentration map and a deposition</p><p>4velocity map: </p><p>5 Dep = Kdep Catmo (3)</p><p>6where Kdep is a map representing deposition velocities and is given by:</p><p> P  K  (v  wP)  (1  )v   dep dep  diff K  7  aw  (3a) </p><p>8where P is precipitation, w is a scavenging factor, vdep is particle deposition velocity, vdiff</p><p>9is velocity of diffusion across the air-surface interface, Kaw is the air-water partitioning</p><p>10coefficient, and  is the fraction of chemical attached to the aerosol phase. </p><p>11 Deposition from the atmosphere sums to direct emission to the soil to compute</p><p>12soil mass balance according to equation (3), and the same for seawater. </p><p>13 The map Koverall in soil is given by: </p><p>E Q VOL 14 K overall     K deg Z (4) R s R L RG</p><p>15 where E is soil erosion rate, Q is water throughflow, VOL is volatilization rate</p><p>16from soil, and RS, RL, RG are coefficients that account for the partitioning of the substance</p><p>17in solid, liquid and gas phase in soils, whereas Kdeg is the degradation rate in soils, and</p><p>18 Z is the soil compartment bulk thickness. </p><p>19 The map Koverall in seawater is given by: </p><p>SETTL VOL 20 K overall    K deg Z (5) R sed Rdiss 1 6</p><p>1 where SETTL is the sediment settling velocity in seawater, VOL is volatilization</p><p>2rate from seawater, RSed, Rdiss are coefficients that account for the partitioning of the</p><p>3substance in sediment-attached and dissolved phase in soils, whereas Kdeg is the</p><p>4degradation rate in seawater, and Z is the seawater compartment mixing depth.</p><p>5 Further details and discussion on the computation of the different parameters in</p><p>6equations (3) to (5) can be found in [23, 38]. Calculation can be iterative, as</p><p>7volatilisation from soil and water provides additional input to the atmosphere, hence new</p><p>8depositions and so on. However, [11] showed that these feedback mass fluxes are often</p><p>9not relevant for most chemicals. A discussion of the model input landscape and climate</p><p>10parameters is in [24]. </p><p>11The main practical strength of a map algebraic approach is the possibility to replace </p><p>12individual algorithms and input data for the calculation of Kdep or Koverall, simply by </p><p>13modifying individual input terms in map algebra expressions, with no need for re-coding </p><p>14numerical models. Moreover, input of individual model parameters is in the form of </p><p>15maps, which allows quick visual data control. </p><p>16Model implementation and benchmarking </p><p>17The equations above described can be easily implemented in any GIS software. The</p><p>18model has been named Multimedia Assessment of Pollutant Pathways in Europe or</p><p>19MAPPE, the Italian word to denote maps. Model assumptions, algorithms and a software</p><p>20developed to run the model in the popular ArcGIS software are presented in [23, 37].</p><p>21 To evaluate the above proposed method, we performed a benchmarking exercise</p><p>22with the EMEP MSCE-POP model ([13]). The evaluation was done using</p><p>23polychlorobiphenyls (PCBs) and polychlorodibenzodioxins/furans (PCDD/Fs), in that 1 7</p><p>1they are relatively well studied, representative persistent organic pollutants (POPs)</p><p>2fulfilling the criteria of [12]. Calculations were performed under steady state</p><p>3assumptions. </p><p>4 The EMEP calculation results for PCBs appear to be quite significantly correlated</p><p>5(Figure 1 Supporting Information (S.I.)). In particular, atmospheric deposition is highly</p><p>6correlated to ocean concentration (94% explained variance), whereas atmospheric</p><p>7concentration is less correlated to deposition (80% explained variance). This suggests that</p><p>8spatial variation in modeled atmosphere deposition rates play a bigger role than variation</p><p>9in modeled ocean removal rate. The soil compartment shows a remarkably lower</p><p>10correlation with the air compartment than ocean, which consistently corresponds to a</p><p>11higher importance of the past history of emissions, and the spatial variation of removal</p><p>12rates in soils. </p><p>13In general, the “water column” model approach used for ocean in the present study does</p><p>14not introduce appreciable errors with regard to the MSCE-POP model, as lateral transfer</p><p>15does not appear important at the working scale of the model. </p><p>16 Table 1 (S.I.) reports the physico-chemical properties used for the chemicals.</p><p>17Table 2 (S.I.) provides the atmospheric emission totals per country, assumed as the only</p><p>18source of emission [18]. Chemical properties are the ones in [13] for PCB 153, and for</p><p>192,3,4, 7,8Cl5DF. The properties of the former have proven to represent reasonably well</p><p>20the behaviour of the sum of PCBs ([17]), while the ones of the latter have been used to</p><p>21describe the total concentration of dioxins and furans as a mixture in terms of toxic</p><p>22equivalents (TEQ) ([20]). </p><p>23Evaluation with monitoring data 1 8</p><p>1 The experimental data to be used for the evaluation of spatially distributed models</p><p>2should be as consistent and homogeneous as possible. Measurements can be quite</p><p>3sensitive to experimental conditions both when sampling in the field, and when</p><p>4performing analyses in the laboratory. In general, it would be preferable to refer to a</p><p>5homogeneous measurement campaign having sufficient representativeness of spatial</p><p>6patterns. Data sets having such features could be found in the case of PCBs for soils [33]</p><p>7and for air [32]. In the case of air passive sampling, it is worth mentioning that the data</p><p>8do not allow a direct comparison with atmospheric concentration as they provide values</p><p>9of chemical mass collected per sample during the measurement period. Nevertheless,</p><p>10there is a correlation between samples mass and atmospheric concentration in the gas</p><p>11phase ([36]), which allows considering the chemical mass per sample as a good proxy of</p><p>12total atmospheric concentration, at least in terms of general spatial trends. Despite being</p><p>13a widely studied class of chemicals, to our knowledge dioxins and furans have not yet</p><p>14been subject, as PCBs, to studies about their spatial distribution yielding georeferenced</p><p>15monitoring data. A compilation of monitoring data was available from [35], while for</p><p>16Swiss soils we referred to the data of [34]. Additionally, a preliminary model evaluation</p><p>17has been performed on the basis of dairy product lipid monitoring. Fatty dairy product</p><p>18samples are easy to collect and handle, and are promising as integrative passive samplers</p><p>19[48], although existing data are still insufficient for extensive evaluation of models. The</p><p>20results of this preliminary evaluation are presented and discussed in the Supporting</p><p>21Information. 1 9</p><p>1Results</p><p>2PCBs</p><p>3Atmospheric concentration (Figure 2 a) follows from the assumption of emissions</p><p>4proportional to national totals and population density, intrinsic in the ADEPT model [31],</p><p>5as clearly shown by some hot-spots that can be immediately linked to large urban areas.</p><p>6A large area with relatively high and uniform concentration is observed in Central</p><p>7Europe, while more peripheral areas show less relevant pollution. Deposition rates</p><p>8(Figure 2 b) follow precipitation, wind, and temperature (determining the air-water</p><p>9partition coefficient according to the exponential law illustrated in [13]), and they</p><p>10correspond to high latitudes and elevations. Areas with reduced air turbulence such as the</p><p>11Po plain in Italy, or Hungary, tend to have lower deposition rates. Deposition fluxes</p><p>12(Figure 2 c) follow atmospheric concentration, although in areas of strong variation for</p><p>13deposition rates, such as the Alps or Great Britain, patterns show some differentiation.</p><p>14The same considerations apply for soil and ocean concentrations (Figure 2 d); locally,</p><p>15variations in soil properties and climate (hence removal rates) may affect the spatial</p><p>16pattern, but the dominant shape of the spatial distribution originates from deposition</p><p>17fluxes. </p><p>18MAPPE and MSCE-POP model results correlation coefficients, and the ratio between</p><p>19mean predicted values of concentrations and deposition fluxes, are reported in Table 3</p><p>20(S.I.). Atmospheric concentration is predicted with relatively good consistency between</p><p>21the MAPPE and MSCE-POP models. MAPPE predicts lower concentrations as about</p><p>2258% of the ones predicted by MSCE-POP (Figure 2 S.I.). The MAPPE model explains</p><p>2388% of the variance produced by the MSCE-POP model. MAPPE predicts also lower 1 10</p><p>1deposition to land surface as about 57% (Figure 2 S.I.). It is to mention that this holds</p><p>2when comparing total (gas + particle phase) deposition of MAPPE with gas phase</p><p>3particle deposition only in MSCE-POP (as this is the result made available by EMEP). As</p><p>4gas phase to particle phase deposition rates ratios in MAPPE are usually in the range of 2</p><p>5to 5, atmospheric particle deposition in MAPPE is consequently lower than 57% of the</p><p>6one in MSCE-POP. </p><p>7The total deposition to the sea predicted by MAPPE is on average about twice as much as</p><p>8particle phase deposition in MSCE-POP (Figure 2 S.I.). According to the same</p><p>9considerations as before, it can be said that atmospheric particle phase deposition to the</p><p>10sea is lower than the one in MSCE-POP. </p><p>11Spatial trends of soil concentration predicted by the MAPPE model are reasonably</p><p>12consistent with the MSCE-POP model (about 40% variance explained), but MAPPE</p><p>13underestimates concentrations of a factor higher than 100 (Figure 3 S.I.), apart from the</p><p>14range of lower concentration values which are within less than one order of magnitude.</p><p>15For sea concentrations, the two models provide a consistent estimate of orders of</p><p>16magnitude, MAPPE predicting higher by about 20% (Figure 3 S.I.), but the correlation</p><p>17between the two models weakens slightly. </p><p>18 Neither the MSCE-POP nor the MAPPE model provide satisfactory correlation with the</p><p>19passive sampler mass distribution (see Figure 4 S.I. for spatial distribution of samples),</p><p>20although both capture a general trend in concentrations (Figure 3) as testified by the least</p><p>21square regression line shown in the graph. Determination coefficients are as low as 0.17</p><p>22for the MSCE-POP and 0.14 for the MAPPE model. The MSCE-POP model, though, is</p><p>23known to predict air concentration reasonably well [18, 19]. 1 11</p><p>1If one considers soil concentrations (see Figure 4 S.I. for spatial distribution of samples),</p><p>2the behaviour of the two models is rather different (Figure 4): the MSCE-POP model</p><p>3shows a very high dispersion of the output values with respect to monitoring data,</p><p>4whereas MAPPE seems to capture trends in a much more consistent way. At the same</p><p>5time, monitoring data suggest that correct soil concentration values should be somewhere</p><p>6in between the ones predicted by MSCE-POP (most of the times overestimating the</p><p>7measurements) and MAPPE (systematically underestimating them above values of about</p><p>81 ng/g, while keeping on the 1:1 line below; this behaviour suggests that for</p><p>9“background” sites the MAPPE model might be unbiased). </p><p>10Dioxins and Furans </p><p>11 Atmospheric concentration (Figure 5 S.I.) closely follows emissions, as in the case of</p><p>12PCBs. Two areas of high atmospheric concentration are highlighted, one corresponding</p><p>13to the big western conurbation spanning from London to Milan, and the other In central</p><p>14Europe. Also Bulgaria is predicted as a hot spot area for atmospheric concentration.</p><p>15Deposition rates (Figure 5 S.I.) follow similar patterns to the ones for PCBs. Deposition</p><p>16fluxes (Figure 5 S.I.) suggest hot spots in Switzerland, Belgium, Czech Republic, and in</p><p>17many large urban areas due to high air concentration. Soil and ocean concentrations</p><p>18follow the same pattern as deposition fluxes (Figure 5 S.I.). </p><p>19Correlation coefficients and the ratio between mean predicted values of concentrations</p><p>20and deposition fluxes are also reported in Table 3 S.I.. Atmospheric concentration is</p><p>21predicted with relatively good consistency between the MAPPE and MSCE-POP models.</p><p>22Although the scatter of the values is slightly wider than for PCBs (R2=0.74), there is no</p><p>23systematic underestimation (Figure 6 S.I.). In this case, however, MAPPE estimates 1 12</p><p>1deposition to both land surface and ocean, on average higher of a factor between 2 and 3,</p><p>2slightly higher for land surface (Figure 6 S.I.). </p><p>3Spatial trends of soil concentration predicted by the MAPPE model are reasonably</p><p>4consistent with the MSCE-POP model, MAPPE estimating concentrations a factor of</p><p>5about 2 lower (Figure 7 S.I.). For sea concentrations, the two models provide a consistent</p><p>6estimate in absolute values, with higher correlation between the estimates than in the case</p><p>7of soils (Figure 7 S.I.). </p><p>8With reference to both the compilation of European monitoring [35], for concentration in</p><p>9soils and the atmosphere, and the more recent survey on Swiss soils [34], MSCE-POP</p><p>10and MAPPE are consistently underestimating air and soil concentration of a factor not</p><p>11less than 10. The spatial trends of concentrations are also showing poor correspondence</p><p>12between monitoring data and model results (Figure 5). </p><p>13Discussion</p><p>14PCB </p><p>15The lower predictions of the MAPPE model with respect to MSCE-POP can be explained</p><p>16in terms of missing sources (such as extra-continental emissions, volatilization from</p><p>17soils). This reason can well account for a difference of about 40% in emissions, hence</p><p>18concentrations [38]. In general, there is no evidence that one of the two patterns is better</p><p>19than the other. From the passive sampler results (Figure 3) it appears that the two scatters</p><p>20are very similar to each other. </p><p>21The two models provide comparable orders of magnitude also of atmospheric deposition,</p><p>22but significant discrepancies may arise when separating particle phase and gas phase. 1 13</p><p>1This critically depends on the fraction of the chemical that the model predicts as being</p><p>2attached to aerosol. Differences up to a factor of 10, depending on the equations used and</p><p>3the value of the parameters, were observed in other model intercomparisons [14]. </p><p>4The large underestimation of soil concentration in MAPPE with respect to the MSCE-</p><p>5POP values can be due to a combination of the following factors: </p><p>6 1) the assumed exponential soil chemical profile of MSCE-POP, results being</p><p>7 referred to the first layer of soil (1 mm); average concentrations in soil can be as</p><p>8 low as 5 to 10% than the one in the top mm of soil [38]; this leads also to higher</p><p>9 soil volatilization, hence atmospheric emissions not accounted for in MAPPE;</p><p>10 2) the effect of past emission history: the transient effects due to the history of past</p><p>11 emissions highlight that soil masses at present days can be as high as a factor of 5</p><p>12 than the ones predicted by steady state balance from present emissions [38];</p><p>13 3) from Figure 3 S.I. total deposition in MAPPE is lower than particle phase</p><p>14 deposition in MSCE-POP on land; this means that a fortiori total deposition is</p><p>15 estimated lower by a factor >2.</p><p>16 The product of the three factors of underestimation due to the reasons discussed</p><p>17above is between 10 x 5 x 2 = 100 and 20 x 5 x 2 = 200, which can justify the</p><p>18discrepancy. It is worth stressing that experimental evidence is not clear about the</p><p>19applicability of an exponential soil concentration profile as suggested in [39], due to the</p><p>20effects of disturbances such as bioturbation, ploughing in agricultural soils, and other</p><p>21factors which tend to homogenize concentrations in topsoil (e.g. [40, 41, 46]). 1 14</p><p>1 The MAPPE model captures a general spatial trend, and the order of magnitude of</p><p>2concentrations, also with respect to measurements in fatty dairy products, as discussed in</p><p>3the S.I.</p><p>4Dioxins and Furans </p><p>5MAPPE and MSCE-POP provide consistent estimates, with no appreciable discrepancy.</p><p>6However, both models produce the same type of underestimation of the monitoring data,</p><p>7about a factor of 10. Part of the underestimation can be linked to emission inventories,</p><p>8which are apparently low. In fact, estimates issued by EMEP while preparing the material</p><p>9for this paper ([19]) showed an increase of emissions by a factor 3 with respect to the</p><p>10ones in [18]. Another issue to address is the time frame of the monitoring data: the data</p><p>11compiled in [35] refer to years from the 1980’s to mid 1990’s, while the model results are</p><p>12obtained with emissions of the year 2001. However, according to EMEP ([18], [19]),</p><p>13during years from 1990 to 2004 the reduction in emissions over Europe was estimated as</p><p>14only 35 %. Other comparisons with model applications show that the trend in</p><p>15underestimation is a common problem. For instance, the EMEP MSCE-POP model</p><p>16updated in 2006 ([19]) still confirms a generally light underestimation, and an inspection</p><p>17of Figure 4 in [11] also suggests that predictions tend to lay towards the lower limit of</p><p>18monitored values, compatibly with an underestimation of a factor of 3 approximately. It</p><p>19is also to be considered that many of the data used for comparison refer to urban</p><p>20environments, where concentrations tend to be significantly higher (up to a factor of 5)</p><p>21than in background locations ([19]). </p><p>22Soil concentration is slightly underestimated by the MAPPE model with respect to</p><p>23MSCE-POP, but still in the same order of magnitude. Unlike for PCBs, the results of the 1 15</p><p>1EMEP model are provided as averages over the top 5 cm of soil. This reduces the effect</p><p>2of the exponential profile already discussed for PCBs. The transient effect in dioxin</p><p>3emissions from 1990 reported in [18], can account for a factor of about 2 [38]. Ocean</p><p>4concentrations appear unbiased and largely dominated by atmospheric deposition. For the</p><p>5case of soils, we observe the same trend in underestimation as for the atmosphere. It is</p><p>6interesting to notice that more recent samples, as in [34], are less underestimated. This</p><p>7supports the conjecture that part of the underestimation on the data of [35] is due to the</p><p>8time period of the samples. </p><p>9 The MAPPE model reproduces a weak spatial trend, as from Figure 5, showing</p><p>10that predictions are within a factor of 10 from observations. The MAPPE model captures</p><p>11the order of magnitude of concentrations with respect to measurements in lipids, as</p><p>12discussed in the S.I., but not the spatial pattern.</p><p>13Perspectives and conclusions</p><p>14 The paper demonstrates the use of the novel MAPPE approach to describe the fate and</p><p>15transport of contaminants in the environment, using GIS analysis only with no need for</p><p>16specialized model codes. The approach has a number of practical advantages, among</p><p>17which virtual independence on resolution (only limited by the available input data),</p><p>18generally low computation time requirements compared to other models, easy</p><p>19identification of the calculation steps that contribute the most to discrepancies between</p><p>20observations and predictions, thanks to the simplicity of algorithms and the possibility of</p><p>21visually inspecting maps of all model parameters. Moreover, model algorithms can be</p><p>22adjusted quickly without any code modification as required instead in traditional models.</p><p>23We show that the model provides results which are consistent with the ones of the much 1 16</p><p>1more sophisticated and comprehensive MSCE-POP model, and we explain discrepancies</p><p>2on the basis of model assumptions adopted for the present study, which may be anyway</p><p>3modified upon strong monitoring evidence. Comparisons with monitoring data, however,</p><p>4highlight that the proposed approach does not perform less accurately, and sometimes can</p><p>5be regarded as preferable, with respect to the MSCE-POP one. The proposed method</p><p>6aims at providing a synergic, and not an alternative tool to the more comprehensive</p><p>7models, that provide insights on more detailed aspects of the mechanics of pollution but</p><p>8may be surrogated by the proposed approach for the purpose of mapping long term</p><p>9averaged spatial distributions of pollutants, integrating monitoring, modeling and</p><p>10emission inventories as suggested in [40]. </p><p>11Acknowledgements</p><p>12The research was partly funded by the European Commission FP6 contract no. 003956 </p><p>13(NoMiracle IP: http://nomiracle.jrc.it ). I thank gratefully V.Shatalov and E.Mantseva </p><p>14from the EMEP MSCE-POP modeling team for providing data, reports and discussion, </p><p>15and colleagues D.Pennington, G.Umlauf, I. Vives Rubio, and M.P.Vizcaino Martinez at </p><p>16the IES of EC DG JRC for their critical reading of versions of the manuscript, and </p><p>17valuable comments and suggestions. </p><p>18References</p><p>19 1. Wegmann, F., The global dynamic multicompartment model CliMoChem for</p><p>20 persistent organic pollutants : Investigations of the vegetation influence, the cold</p><p>21 condensation and the global fractionation. Diss., Naturwissenschaften,</p><p>22 Eidgenössische Technische Hochschule ETH Zürich, Nr. 15427, 2004 1 17</p><p>1 2. Pennington, D.W., M. Margni, C. Amman and O. Jolliet, 2005. Multimedia fate</p><p>2 and human intake mod-eling: spatial versus nonspatial insights for chemical</p><p>3 emissions in Western Europe. Environmental Science and Technology 39: 1119-</p><p>4 1128</p><p>5 3. Prevedouros, K., M. McLeod, K.C. Jones and A.J. Sweetman, 2004. 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Hollander, A., Iris Baijens, Ad Ragas, Mark Huijbregts and Dik van de Meent,</p><p>17 Validation of predicted exponential concentration profiles of chemicals in soils,</p><p>18 Environmental Pollution, Volume 147, Issue 3, June 2007, Pages 757-763.</p><p>19 47. Fenner, K. Scheringer, M. MacLeod, M. Matthies, M., McKone, T.E., Stroebe,</p><p>20 M., Beyer, A., Bonnell, M., Le Gall, A.-C., Klasmeier, J., Mackay, D., van de</p><p>21 Meent, D., Pennington, D.W., Scharenberg, B., Wania, F. (2005): Comparing</p><p>22 Estimates of Persistence and Long-Range Transport Potential among Multimedia</p><p>23 Models, Environmental Science and Technology 39, 1932–1942. 1 24</p><p>1 48. Santillo, D., Fernandes, A., Stringer, R., Alcock, R., Rose, M., White, S., Jones,</p><p>2 K., Johnston, P., Butter as an indicator of regional persistent organic pollutant</p><p>3 contamination: further development of the approach using PCDD/Fs and PCBs,</p><p>4 Food Additives and Contaminants, 2003, vol. 20, no. 3, 281-290. 1 25</p><p>1</p><p>Emissions air Overall average (national totals) air removal rate for Europe </p><p>Source-receptor maps Air concentration map</p><p>Time-of-travel maps</p><p>Landscape and climate K map maps dep </p><p>Atmospheric K map, overall deposition map water Scalar physico- chemical properties: K , K , K map, soil ow, aw, overall molecular weight , , degradation rate, air , , degradation rate, soil , Soil Water , concentration concentration degradation rate, map map water.</p><p>Emissions soil Emissions water</p><p>2Figure 1 – logics of the map calculations. In grey input data (grey boxes are maps, grey text scalars); </p><p>3in black boxes, output maps. 1 26</p><p>1a b</p><p>2c d</p><p>3</p><p>4Figure 2 – atmospheric concentration (a), deposition rate (b), soil and sea concentration (c) and </p><p>5deposition fluxes (d) for PCBs, as predicted by the MAPPE model.</p><p>6 1 1</p><p>1E+03 g n</p><p> s</p><p> s 1E+02 a m</p><p> r e l p m a s</p><p> e</p><p> v 1E+01 i s s a p</p><p>1E+00 1E-03 1E-02 1E-01 1E+00 predicted concentration ng m-3 2 A</p><p>1E+03 g n</p><p> s</p><p> s 1E+02 a m</p><p> r e l p m a s</p><p> e</p><p> v 1E+01 i s s a p</p><p>1E+00 1E-03 1E-02 1E-01 1E+00 predicted concentration ng m-3 3 B</p><p>2 1 28</p><p>1Figure 3 – model evaluation for PCBs with air passive samplers: (A) MSCE-POP model; (B) MAPPE</p><p>2model 1 29</p><p>1 </p><p>MAPPE</p><p>1000</p><p>100</p><p>10 l e d o m</p><p> g / g n</p><p>C 1 0.1 1 10 100</p><p>0.1</p><p>0.01 C ng/g monitoring 2 1 30</p><p>MSCE-POP</p><p>1000</p><p>100</p><p>10 l e d o m</p><p> g / g n</p><p>C 1 0.1 1 10 100</p><p>0.1</p><p>0.01 C ng/g monitoring 1</p><p>2Figure 4– model evaluation for PCBs with soil samples. Lines 1:1 and a factor 10 interval are </p><p>3displayed. 1 31</p><p>1</p><p> soil 1:1 obs / 10 air soil (Schmid et al., 2005) obs X 10 </p><p>10000</p><p>1000 n o</p><p> i 100 t a r t n e c n</p><p> o 10 c</p><p> d e t u p</p><p> m 1 o c</p><p>0.1</p><p>0.01 0.01 0.1 1 10 100 1000 observed concentration 2</p><p>3Figure 5 – scatter diagram of observations and calculation results for dioxins. Values are in ng I-</p><p>4TEQ /Kg dm for soils and fg I-TEq / m3 for air. Data refer to the MAPPE model prediction, while </p><p>5the MSCE-POP ones are very similar and not reported for simplicity.</p><p>6</p>

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