H COMPARISON AND EVALUATION OF THE 1KM AND 5KM RESOLUTION FRAME MODELLED ANNUAL CONCENTRATIONS OF NITROGEN OXIDES

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1 H4-6 COMPARISO AD EVALUATIO OF THE KM AD 5KM RESOLUTIO FRAME MODELLED AUAL COCETRATIOS OF ITROGE OXIDES Macej Kryza, Anthony J. Dore 2, Małgorzata Werner, Marek Błaś Wrocław Unversty, Department of Clmatology and Atmosphere Protecton, Wrocław, Poland 2 Centre for Ecology and Hydrology, Ednburgh, UK Abstract: The am of ths paper was to compare and evaluate the modelled annual O x ar concentratons calculated for the same area at two dfferent grd resolutons of km x km and 5km x 5km. The Fne Resoluton Atmospherc Mult-pollutant Exchange model (FRAME) was used for ths ssue and the domans were defned to cover the entre area of Poland. Two smulatons were performed for the year 2005 and The nput fles for the model were provded separately for both km and 5km grds, but t was assured that the emsson, meteorologcal and boundary condton data were kept constant n terms of e.g. total mass. Ths was done by aggregaton of km data nto the 5km model grd. The km and 5km model runs resulted n a smlar spatal pattern and country average value of O x ar concentratons. The maxmum values were sgnfcantly hgher for the km x km doman. For the hgh resoluton doman the emsson source areas were also dstnctly separated from the background regons of low concentratons. For the 5km doman, 3 rd quartle of grdded ar concentratons was hgher than for km x km run. The evaluaton of the km and 5km results shows that the model measurement agreement s mproved for the hgh resoluton smulatons. The mean bas and average error statstcs were decreased. The correlaton coeffcent was also hgher for the km doman, wth the excepton of the urban statons n year 2008, whch was attrbuted to the hgher uncertanty of the emsson nventory. Key words: spatal resoluton, ar qualty model, ntrogen oxdes, FRAME ITRODUCTIO Atmospherc transport models (ATM) are mportant tools supportng envronmental management and provde spatally contnuous nformaton on current, past and future ar qualty. The ATM provded grdded nformaton s used, among others, for the assessment of the crtcal levels and loads exceedances and populaton exposure to protect human health and ecosystems (IIASA, 2005; RoTAP, 2009). The large number of models and ther varous confguraton often leads to dfferent results of estmated spatal patterns of concentraton and deposton of atmospherc pollutants. Hallsworth et al. (200) show that the varous resolutons used for calculaton of ammona ar concentratons leads to sgnfcant dfferences n areas wth crtcal level exceedances for ammona and may further results n nsuffcent or unnecessary and costly protecton of the ecosystems. The reason for ths s the spatal averagng of the model nput and output nformaton wth the ncreasng grd sze. Denby et al. (20) reported that nsuffcent spatal resoluton of the ar qualty model results n sgnfcant underestmaton of the urban background exposure for ntrogen doxde. The spatal resoluton of the model mesh s also mportant for deposton of ntrogen and sulphur compounds, especally n a complex terran or n the vcnty of the emsson sources (RoTAP, 2009). The am of ths paper s to present and compare the results of O x ar concentraton modellng wth the Fne Resoluton Atmospherc Mult-pollutant Exchange (FRAME) model appled for Poland wth the spatal resolutons of km x km and 5km x 5km. The smulatons are run for the years 2005 and The results are compared both vsually and statstcally. The model estmates of annual average O x are compared wth the ar qualty measurements gathered at background rural and urban statons. DATA AD METHODS Descrpton of the FRAME model FRAME s a Lagrangan statstcal trajectory model that s used for the Unted Kngdom and Poland to support envronmental management and protecton. A detaled descrpton of the model s provded by Sngles et al. (998), Fourner et al. (2005), and Dore et al. (2007). Detals on the model confguraton specfc for Poland are provded by Kryza et al. (200). The model provdes nformaton on annual ar concentratons and deposton of ntrogen and sulphur compounds and prmary partculate matter. Here the 8.3 verson of the model s appled, and the smulatons are run for the two domans coverng the area of Poland wth km x km (Dkm) and 5km x 5km (D5km) spatal resolutons. The Dkm mesh s composed of 800 x 800 grds, and D5km s of sze 60 x 60 grds. The spatal extent of the Dkm and D5km domans are the same. For each doman, separate nput data on emsson, precptaton and landuse were prepared. For the D5km, the emsson, ranfall and landuse data were developed by aggregaton of the Dkm fles, to assure spatal homogenety e.g. n terms of mass of emtted pollutants or amount of annual precptaton. The boundary condtons were calculated wth the FRAME-Europe model, and appled for Dkm and D5km after re-grddng nto km x km and 5km x 5km grd, respectvely. The regrddng process dd not affect the total mass of the pollutants mported nto the Dkm and D5km domans. Emsson nventory for the year 2005 and 2008, avalable from Dębsk et al. (2009) were used n ths study. The emsson data were provded at km x km grd resoluton, and aggregated nto 5km x 5km grd for the D5km model runs. For both years selected, the year specfc wnd and precptaton data were used. Smlarly to the emsson nventory, meteorologcal data for D5km were developed by aggregaton of the Dkm fles. It should be notced that for emsson calculaton from road traffc, detaled nformaton on traffc ntensty were avalable only for the year Ths nformaton was also used to develop the emsson map for the year Therefore the uncertanty related wth emsson nventory s hgher for the year 2008, especally over the areas where road transport s the major source of ntrogen oxdes for the atmosphere (e.g. large urban areas). Topc : Model Evaluaton and Qualty Assurance 25

2 Evaluaton of the model results Annual average O x ar concentratons calculated by the FRAME model were compared wth the measurements performed on Polsh ar qualty network and provded through the ArBase database. The completeness of the measurements used for calculaton of annual average value was above 90% for all statons. For the model measurement comparson, only background urban (BU) and background rural (BR) statons were used. For each year, confguraton of the measurng network dffer sgnfcantly, both n terms of total number of stes and fracton of urban and rural statons (Table ). There was a sgnfcant ncrease n total number of measurng stes from year 2005 to However, the ncrease was manly n the number of background urban stes, whle the BR stes remaned sparse. The new statons n year 2008 were located manly n large ctes (Fg. ). Table. Summary of the O x measurng stes for year 2005 and 2008 used for model evaluaton Type of staton Year 2005 Year 2008 Background urban 44 8 Background rural 4 2 Total number of stes The model error was calculated for each ste as a dfference between model (M ) calculated and observed (O ) value. To summarze the model performance, the followng error statstcs were used (Yu et al. 2006): Mean Bas MB = ( M O ) Mean Absolute Gross Error MAGE = M O Root Mean Squared Error RMSE = ( ) M O 2 () (2) (3) The error statstcs were calculated separately for BU and BR stes. The set of error metrcs was complmented by the Pearson correlaton coeffcent (R). The modelled measured values are also presented on the scatter plots. For each measurng ste, relatve error (RE) was calculated and marked on maps, accordng to the formula: RE M O = (5) O RESULTS In general, both Dkm and D5km model runs gve smlar spatal pattern of O x annual average ar concentratons. Man ctes are the areas of the hghest ar concentratons (Fg. ), and the man roads are recognzable on both Dkm and D5km maps. For the Dkm model setup, there s a strong separaton of the emsson source areas wth hgh values of O x ar concentratons from the background regons, especally along the man roads crossng the relatvely clear areas. There s no tendency for clusterng the statons wth large or small relatve errors, e.g. n the ctes or over the background regons. The hghest RE has been calculated for the same statons for Dkm and D5km. In year 2005 the staton wth the hghest RE s the urban staton (Torun) for whch the RE s.9 and 0.9 for Dkm and D5km, respectvely. For the year 2008, the maxmum RE s for mountanous Snezka staton (SW Poland), wth the RE equal to 3.2 and 3.5. The grd average O x concentratons are at smlar levels for both domans (Fg. 2), reachng 6.9 and 7.0 μg m -3 n year 2005 for Dkm and D5km, and 7.7 and 7.8 μg m -3 n year For both years, the Dkm smulatons results n sgnfcantly hgher maxmum and lower mnmum values of O x (68. for Dkm and 52.6 μg m -3 for D5km n 2005, for year 2008 the respectve values are 83.3 and 63.8 μg m -3 ). Ths s related to the mentoned above strong separaton of the source and background areas. For the D5km model doman, the concentratons are averaged over the larger grds, and ths s the reason for decreased maxmum values f compared to Dkm. For the same reason, the 3 rd quartle s shfted towards the hgh values for D5km runs. 26

3 Fgure. Modelled km and 5km O x concentratons for years 2005 and 2008 and RE for each of the O x measurng stes Fgure 2. Statstcal summary of the modelled km and 5km O x ar concentratons for years 2005 and 2008 The model measurements comparson s presented n Fg. 3. For the Dkm, the number of stes that fall below or above :2 and 2: lnes s lower than for D5km for both years. The Dkm model run gves overall hgher O x ar concentratons for urban statons, whch results n decreased MB (Table 2), especally for the year 2008, and for some stes ths s the reason for Topc : Model Evaluaton and Qualty Assurance 27

4 the overestmaton of the observed values. However, the Dkm model stll have a general tendency for underestmaton of the annual O x ar concentratons for both urban and rural statons, reflected n the negatve mean bas for both years 2005 and 2008, wth the excepton of the rural stes for the year Both statstcs of the average error, MAGE and RMSE, suggest the mproved performance of the Dkm over the D5km. The average errors are lower for both urban and rural statons. For the rural statons, the correlaton coeffcent s also hgher for the Dkm model run than for 5km grd. However, there s relatvely poor correlaton for the urban stes n year 2008, and the R value s smaller for the Dkm. The smaller R for the year 2008 can be explaned by the uncertanty n the traffc emsson nventory, whch brngs the majorty of emtted ntrogen oxdes, and s based on traffc flow measurements performed n year 2005 and rescaled to the year The greater uncertanty n mappng hgh resoluton emssons data can be also the reason for smaller R for the year 2008 Dkm smulaton, f compared wth D5km, for whch the errors may be averaged out resultng n an mproved R value Fgure 3. Modelled vs. measured O x ar concentratons for urban and rural statons n year 2005 (left) and 2008 (rght) Table 2. Error statstcs for urban and rural statons for km and 5km model runs Year Model Urban statons Rural statons grd MB MAGE RMSE R MB MAGE RMSE R 2005 km km km km SUMMARY AD COCLUSIOS The man am of ths paper was to compare the FRAME modelled annual ar concentratons of O x for two doman of dfferent spatal resolutons for the area of Poland. The model was run for two years: 2005 and Apart from the vsual and statstcal comparson of the estmated O x concentratons, the model results were evaluated by comparson wth background rural and urban ar qualty measurements. Both km and 5km smulatons estmated smlar country average values of annual O x concentratons. Ths s n accordance wth the fndngs reported by Stroud et al. (20) for organc aerosols wth the AURAMS model runnng wth three dfferent spatal resolutons (42, 5 and 2.5 km). The km FRAME model gves locally sgnfcantly hgher maxmum values, but the 5km model estmate hgher concentratons for larger areas of the country, what s descrbed by the hgher values of the 3 rd quartle. Ths s mportant n terms of crtcal levels exceedances and may be the reason for nsuffcent or unnecessary protecton of the area. Ths ssue should be also examned for other atmospherc pollutants, especally for partculate matter, because of ts strong adverse mpact on human health and large spatal varaton of emsson of prmary partcles and gaseous precursors for the secondary aerosols (e.g. ammona and sulphur doxde). There FRAME model runs for a hgh resoluton mesh of km x km are n overall better agreement wth the O x ar concentratons measurements. The MB and average errors, MAE and RMSE, are decreased when hgher spatal resoluton s appled for both urban and rural stes. The only excepton s the correlaton coeffcent calculated for the urban stes n year 2008, whch can be attrbuted to the hgher uncertanty related wth the emsson nventory used. 28

5 All the fndngs summarzed above ndcate the mportance of the spatal resoluton of the doman setup for the fnal results that the model can provde. The better model measurement agreement calculated for the km doman suggest that the ncrease of resoluton may result n mproved estmates of chemcal composton of the ar. However, the ncrease n resoluton must go together wth the qualty of the nput data, as the errors resultng e.g. from the wrong spatal allocaton of emsson are not averaged out at hgh resolutons. ACKOWLEDGEMETS The work was funded by the Polsh Mnstry of Scence and Hgher Educaton grant nr REFERECES Denby, B., M. Cassan, P. De Smet, F. De Leeuw, J. Horalek, 20: Sub-grd varablty and ts mpact on European wde ar qualty exposure assessment. Atmos. Envron., 45, Dębsk, B., K. Olendrzyńsk, J. Ceślńska, I. Kargulewcz, J. Skośkewcz, A. Olecka, K. Kana, 2009: Inwentaryzacja emsj do powetrza SO2, O2, CO, H3, pyłów, metal cężkch MLZO TZO w Polsce za rok IOŚ, KCIE. Dore, A.J., M. Veno, Y.S. Tang, U. Dragosts, A. Doso, K.J. Weston, M.A. Sutton, 2007: Modellng the Atmospherc Transport and Deposton of Sulphur and trogen over the Unted Kngdom and Assessment of the Influence of SO2 Emssons from Internatonal Shppng. Atmos. Envron.,, Fourner,., Y.S. Tang, U. Dragosts, Y. De Kluzenaar, M.A. Sutton, 2005: Regonal Atmospherc Budgets of Reduced trogen over the Brtsh Isles Assessed Usng a Mult-Layer Atmospherc Transport Model. Water Ar Sol Pollut., 62, Hallsworth, S., A.J. Dore, W.I. Bealey, U. Dragosts, M. Veno, S. Hellsten, Y.S. Tang, M.A. Sutton, 200: The role of ndcator choce n quantfyng the threat of atmospherc ammona to the 'atura 2000' network. Env. Sc. Polcy, 3, IIASA, 2005: CAFE Scenaro Analyss Report r. 6, A Fnal Set of Scenaros for the Clean Ar For Europe (CAFE) Programme.URL (20) Kryza, M., M. Werner, M. Błaś, A.J. Dore, M. Sobk, 200: The Effect of Emsson from Coal Combuston nonndustral Sources on Deposton of Sulfur and Oxdzedtrogen n Poland. J. Ar & Waste Manage. Assoc.,60, RoTAP, 2009: Revew of transboundary ar polluton. Acdfcaton, Eutrophcato, Ground Level Ozone and Heavy Metals n the UK. URL (200) Sngles, R., M.A. Sutton, K.J. Weston, 998: A Mult-Layer Model to Descrbe the Atmospherc Transport and Deposton of Ammona n Great Brtan. Atmos. Envron.,32, Stroud, C.A., P.A. Makar, M.D. Moran, W. Gong,, S. Gong, J. Zhang, K. Hayden, C. Mhele, J.R. Brook, J.P.D. Abbatt, J.G. Slowk, 20: Impact of model grd spacng on regonal- and urban- scale ar qualty predctons of organc aerosol. Atmos. Chem. Phys.,, Yu., S., B. Eder, R. Denns, S. Chu, S. Schwartz, 2006: ew unbased metrcs for the evaluaton of ar qualty models. Atmos. Sc. Let.,7, Topc : Model Evaluaton and Qualty Assurance 29