4.05 MODA A HYBRID ATMOSPHERIC POLLUTANT DISPERSION MODEL. Servizi Territorio srl, Milan, Italy

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9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes 4.5 MODA A HYBRID ATMOSPHERIC POLLUTANT DISPERSION MODEL M. Favaron, O. Olvet Selm, R. So Serv Terrtoro srl, Mlan,
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9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes 4.5 MODA A HYBRID ATMOSPHERIC POLLUTANT DISPERSION MODEL M. Favaron, O. Olvet Selm, R. So Serv Terrtoro srl, Mlan, Ital Agena Regonale Proteone Ambente (ARPA) Lao, Ret, Ital DESCRIPTION OF THE MODA ATMOSPHERIC POLLUTANT DISPERSION MODEL MODA s a Gaussan-hbrd atmospherc dsperson model, ntended for regulator applcatons, and desgned to meet the followng requrements: Ablt to operate n complex terran. Standard use of a refned descrpton of turbulence. Operatonal effcenc (n terms of both speed and ease to change smulaton parameters). Ease of ntegraton n modellng nterfaces. Output compatblt wth the wdel-used ISC3. MODA can operate n two modes: A standard mode, n whch the pollutant dsperson s treated as Gaussan, and An advanced mode, n whch the hbrd relatons are used to compute the pollutant concentratons. In the standard mode, of specal relevance n the context of envronmental mpact assessment, the pollutant concentraton s calculated usng two separate sets of relatons for stable and convectve stuatons. Under stable condtons, concentraton s modelled as ( ) h C x,,; u = exp exp () πσ σ u σ where denotes the pollutant emsson rate (g/s), h the stack tp heght above ground (m), and u the wnd speed (m/s). Under convectve condtons, where q( x,,; u, ) ( ) = exp C x,,; u, () σ u - 6 - 9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes q πσ h + h h exp + exp + exp h + β + β cos π π ( ) = ( β x,,; u ) π h h.8 h .8 (3) σ wth β = exp π. In both cases, the wnd feld s assumed unform n space, and streamlne coordnates are used, so that x represents downwnd dstance from the source, the crosswnd dstance from the source, and the vertcal elevaton; the dependence of concentraton on downwnd dstance s ndrect, occurrng through the horontal and vertcal standard devatons. Unstable condtons are detected b the decson predcate H =. The turbulent sensble heat flux H s read from the meteorologcal nput, along wth other turbulence and PBL parameters. At the moment, all of these can be drectl measured b surface meteorologcal statons equpped wth an ultrasonc anemometer and runnng edd-covarance methods, wth the onl excepton of the mxng heght. The latter has been estmated usng Grnng- Batchvarova method. For statons where no ultrasonc anemometer stll exsts, estmaton of turbulence parameters can be made b emplong smlart relatons, provded a mnmum nstrument set s operatng n place. MODEL VALIDATION The overall MODA valdaton s a work n progress, whose fnal result s expected b end of Aprl 4. The result evaluaton s currentl n progress, and ts outcome wll be ncluded n the poster. COMPARISON TO ISC3 MODA (operated n standard mode) has been compared to ISC3 n varous natural and artfcal stuatons. The followng graphs llustrate the two models' dfferent behavour aganst two artfcal cases, dfferng for stack heght (8m n case A, m n case B). In both cases, emsson s markedl buoant (release temperature C). Source poston s dentcal n the two cases, wth the sngle stack placed at the centre of a xkm test area. Meteorolog s artfcall generated, wth wnd exercsng sstematcall all possble provenance drectons; 5 smulated das are present, wth an equal occurrence of stable and unstable condtons. The evaluaton of concentraton dfference has been made on a grd of nodes along x axs, and along axs; onl the ponts where at least one of the ISC3 and MODA concentratons s greater than have been used 9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes Relatve Frequenc Case A - Dfference n N Ox Concentraton MODA - ISC3 (ug/m3) Case B - Dfference n NOx Concentraton MODA - ISC3 (ug/m3) Fgure. Hstograms of the dfference between MODA and ISC concentratons The man statstcs assocated wth the varable C = C MODA C ISC 3 n the two cases are gven n table : Table. Statstcs of C = C MODA C ISC 3 Case A (Stack tp = 8m) Case B (Stack tp = m) Number of values Mnmum Maxmum Mean Medan Standard devaton Coeffcent of varaton Skewness Kurtoss In nether case the dstrbuton of varable C appears normal, as suggested b the large values of skewness and kurtoss. Nonetheless, MODA and ISC3 provde comparable values, wth a tendenc of MODA to overestmate wth respect to ISC3, as suggested b both the mean and the medan. The actual overestmaton amount s greater for the lower stack tp heght: ths has been traced to the buoanc parameteraton adopted n ISC3, attrbutng the stack plume under unstable condtons an asmptotc heght n excess of 5m n the cases analsed. EFFECT OF COMPLEX TERRAIN The maps n fgure llustrate the dfference between flat and complex terran MODA runs, an other condton fxed 9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes Fgure. Hourl NO x concentraton map, wthout (left) and wth (rght) terran elevatons The scheme used for modellng concentratons on a complex terran matches the one adopted b Aermod, based on the decomposton of the plume n a terran-followng and a constant heght sub-plumes. The parttonng of concentraton between the two plumes s based on current stablt, measured on a fne scale b turbulence parameters. Implementaton of the crtcal heght and parttonng coeffcent computng has been optmsed for effcenc, usng a lnearaton of the equatons generall used. Valdaton of complex terran data has not et been done, and s one of the pendng development goals n the MODA project. CONCLUSIONS AND FURTHER PLANNED DEVELOPMENTS At the date of ths abstract s wrtng, MODA has been confrmed to be a sensble alternatve to ISC3 when pont sources are consdered. Its man feature, namel the ablt to use data from the dffusng advanced meteorologcal statons, allows to model the effects of PBL turbulence usng contnuous parameters nstead of categorcal varables than ISC3. In the next future, MODA wll undergo varous planned extensons: Ablt to use vertcal wnd profles (both smlart and measured); Extenson to coast stes; Through testng and valdaton to European and nternatonal data sets. The authors are evaluatng to place the text-nterface edton of MODA n the publc doman, usng a GPL or smlar lcense, so that a large audence s reached and valuable comments can be gathered 9 th Int. Conf. on Harmonsaton wthn Atmospherc Dsperson Modellng for Regulator Purposes REFERENCES Berkowc R, H.R. Olesen and U. Torp, 998: The Dansh Gaussan ar polluton model (OML): Descrpton, test and senstvt analss, n vew of regulator applcatons. In W.C de Wspelare, F.A. Schermeer and N.V.Gllan, Ar Polluton Modelng and ts Applcatons, eds. Plenum, New York, pp Berkowck R., H.R. Olesen and P. Lofstrom, : OML: An Operatonal Atmospherc Dsperson Model, The Dansh Regulator Model, draft. Grnng S.E. and E. Batchvarova, 99: Smple model of the datme boundar laer heght, Nnth Smposum on Turbulence and Dffuson, AMS, Rosklde, Denmark So R. and D. Fraternal, 993: PBL_MET Lbrar. A software lbrar for Advanced Meteorologcal and Ar ualt Data Processng (Fortran 77 and C Versons). Presentaton at the II Workshop on European Harmonsaton of Atmospherc dsperson Modellng sstems, Manno, Swterland So R., T. Georgads and M. Valentn, : Introduone alla turbolena atmosferca Concett stme msure, Ptagora Edtrce, Bologna US-EPA, 998: AERMOD Descrpton of Model Formulaton; AERMIC Report for the US- EPA Offce of Ar ualt Plannng and Standards, Research Trangle Park, NC 77, Verson: 9834 (AERMOD and AERMET), 98 (AERMAP) US-EPA, 995: User s gude for the Industral Source Complex (ISC3) Dsperson Model / Volume I User Documents. US-EPA Offce of Ar ualt Plannng and Standards, Research Trangle Park, NC 77, Report number: EPA-454/B-95-3a
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