C i. B i. C 0 local. C 0 trb

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1 JP1.1 THE USE OF AIR QUALITY MODELS TO ESTIMATE THE LOCAL AND TRANSBOUNDARY INFLUENCE DURING SMOG EPISODES Glles Morneau * Nedka Pentcheva Meteorologcal Servce of Canada, Montreal, Canada 1. INTRODUCTION The Canadan federal, provncal and terrtoral jursdctons sgned the Canada Wde Standard (CWS) agreement for ozone and partculate matter n 2000 (Canadan Councl of Mnsters of the Envronment, 2000). Ths agreement establshes numercal targets and tmeframes for achevng the Standards wthn each jursdcton. The man motvaton of ths work s the begnnng of an annual reportng on achevement of the Standards n The achevement determnaton of the numercal targets nvolves removng all the daly exceedances of the Standard that are not under the control of the jursdcton. These are exceedances due to natural events, to hgh background levels and to transboundary flow of smog precursors. Ths work shows the applcaton of an ar qualty model to determne f a gven exceedance of the daly CWS metrc s prmarly due to transboundary flow or not. 2. CALCULATION OF THE LOCAL AND TRANSBOUNDARY CONTRIBUTION TO SMOG In order to determne f an ozone or PM 2. exceedance s due to transboundary flow or to sources wthn the jursdcton, the followng hypothess s made. The measured concentratons n a Reportng area can be represented as the sum of a background, a local and a transboundary contrbuton. The background concentraton s ndependent of long range transport of speces from anthropogenc sources, but s rather a functon of the natural envronment, ncludng the emsson and transport of bogenc speces. To estmate the three terms, an ar qualty model wll be used. * Correspondng author address : Glles Morneau, Meteorologcal Servce of Canada, Quebec Regon, 100 Alexs-Nhon, sute 300, Sant-Laurent (QC), Canada H4M 2N8; e-mal : glles.morneau@ec.gc.ca. Three emsson scenaros wll be run, one wth all anthropogenc emssons (base case), a second wth anthropogenc emssons set to zero wthn the jursdcton and a thrd wth anthropogenc emssons outsde the jursdcton set to zero. Let s defne the followng quanttes : C C m C j 0 C jn 0 B C local C trb Measured concentraton at locaton Model concentraton at locaton obtaned wth all anthropogenc emssons Model concentraton at locaton obtaned wth anthropogenc emssons wthn the jursdcton set to zero Model concentraton at locaton obtaned wth anthropogenc emssons outsde the jursdcton set to zero Background concentraton at locaton Contrbuton of the jursdcton to total concentraton at locaton Transboundary contrbuton to total concentraton at locaton The followng equaton summarzes the hypothess : m local trb C = B + C + C (1) The scenaro wth all anthropogenc emssons wthn the jursdcton set to zero must lead to a local contrbuton equal to zero. Smlarly, the scenaro wth all anthropogenc emssons outsde the jursdcton set to zero leads to a transboundary contrbuton equal to zero. These statements can be substtuted n equaton (1) and one obtans : j C 0 trb = B + C (2) jn C 0 local = B + C (3) Equatons 1-3 can now be solved for the three unknowns, the background, the local and the transboundary contrbutons : j 0 jn 0 B = C + C C local m j 0 C = C C trb m jn 0 C = C C m (4) 1

2 The Gudance Document on Achevement Determnaton (Canadan Councl of Mnsters of the Envronment, 2002) gves a methodology to determne f a daly exceedance of the Standard s manly due to transboundary flow. When ar qualty modellng s performed, an exceedance s qualfed as transboundary nfluenced f the daly value at the montor contnues to be wthn 10% or above the Standard after removng the local contrbuton (as computed from equaton 4) from the actual measurement. In mathematcal terms, an exceedance s transboundary nfluenced f : local C C CWS () threshold where CWS threshold s set to 10% below the daly Standard. For ozone, the daly value s the maxmum of the 8-hour runnng average of hourly concentratons wth the Standard set to 6 ppb. For PM 2., the daly value s the 24-hour average of the hourly concentratons wth the Standard set to 30 µg/m 3. As a result, the thresholds are : For ozone : CWS threshold = 9 ppb For PM 2. : CWS threshold = 27 µg/m 3 It has to be noted that the terms on the left hand sde of equaton are not any more nstantaneous values of the concentratons, but are the daly metrcs of the Standard. To ascertan the valdty of the formulaton, a more strngent crtera to qualfy an event as transboundary nfluenced s evaluated n ths study. It ncludes the above crtera (equaton ) plus a second one. The exceedance would be qualfed as transboundary nfluenced f the concentratons at the montor drops below 10% of the Standard after removng the transboundary contrbuton (as computed from equaton 4) from the actual measurement. In mathematcal term, an exceedance s transboundary nfluenced f s satsfes equaton () and the followng : trb C C < CWS (6) threshold where the thresholds are the same as above. 3. DESCRIPTION OF THE ATMOSPHERIC MODELS AND THE SIMULATED EPISODES The meteorologcal model selected to drve the ar qualty model s the Global Envronmental Multscale model (GEM) of the Meteorologcal Servce of Canada (Côté, 1998). GEM s based on the fully compressble Euler equatons solved by an mplct and sem-lagrangan method. The ntegraton doman covers all North Amerca at a resoluton of 24 km. The grd has 28 levels along the vertcal axs and the model top s set at 10 mb. The bottom 7 levels are n the planetary boundary layer. The ar qualty model used n ths study s AURAMS recently developed by the Meteorologcal Servce of Canada (Moran, 1998; Makar, 2003a; Bouchet, 2003). AURAMS s a source based euleran model lnkng emssons to the atmosphere and ambent ar concentratons and deposton. The treatment of transport and advecton s based on the CHRONOS model (Pudykewcz, 1997). The gas phase chemstry s taken from the Acd Deposton and Oxdant Model (ADOM) (MacDonald, 1993) wth 114 reactons and 47 speces. The model ncludes aqueous phase chemstry as well as heterogeneous phase chemstry (Makar, 2003b). The aerosol module s based on the Canadan Aerosol Module (Gong, 2003). Ths aerosol module s sze-resolved wth 12 bns coverng partcle szes from 0.01 to mcrons and ncludes 8 chemcal components : sulphate, ntrate, ammonum, sea salt, black carbon, organc carbon, crustal materal and water. AURAMS was run on a doman coverng Northeastern North Amerca (fgure 1) on a grd wth 12 x 110 ponts and a resoluton of 21 km. The meteorologcal felds needed by the model were obtaned from the GEM model outputs by nterpolaton. The nput anthropogenc emsson rates were based on the natonal nventores processed wth the Canadan Emsson Processng System (CEPS1.0) (Moran, 1997). The bogenc emssons were computed wth the Bogenc Emsson Inventory System verson 2 (BEIS-2) (Geron, 1994) Ths study focusses on ozone and PM 2. exceedances n the Quebec porton of the Wndsor-Quebec cty corrdor. Ar qualty measurements of 1999 to 2001 were analysed and a lmted number of epsodes were selected so as to nclude exceedances due to local sources and to transboundary flow. Three epsodes wth exceedances of the Standard for ozone and/or PM 2. n 1999 and 2001 were smulated wth the models. They are : July 11-18, 1999 June 12-21, 2001 July 29-August 4,

3 URS DSA Montreal WBZ Toronto New York Fgure 1 : AURAMS modellng doman. The stes referred to n ths study are also shown. They are St. Ancet (WBZ), Tros-Rveres (URS) and Quebec Cty (DSA). 4. EVALUATION OF THE MODEL Snce AURAMS has not yet been evaluated over Southern Quebec, an evaluaton of the PM 2. concentratons was performed at three stes along the St. Lawrence valley. An evaluaton of the ozone concentratons s not performed n ths work snce ths module s dentcal to the CHRONOS module whch has been evaluated many tmes wth very satsfactory results. The locaton of the stes for the PM 2. evaluaton are shown on fgure 1. St. Ancet s located southwest of Montreal whch s a major source of smog precursors. Tros-Rveres and Quebec Cty are located northeast of Montreal and, on days wth smog, are usually downwnd of Montreal whereas St. Ancet s upwnd. Snce ths study focusses on the Canada Wde Standards, the comparson between the model values and measurements wll be lmted to the daly average of the PM 2. concentratons. The AURAMS model outputs PM 2. concentratons every hour at every grd pont and several heghts above ground. The frst level near the ground was selected as ths s the closest to the usual heght where measurements are taken. The model concentratons were then nterpolated lnearly to the locaton of three stes, then the daly average concentraton was computed. The followng fgure 2 shows the observed values (PM2 Obs) and the model values (PM2 AURAMS). The local and transboundary contrbutons as computed wth equaton (4) are also shown on the fgure and wll also be dscussed. PM 2. concentratons (µg/m 3 ) PM 2. concentratons (µg/m 3 ) PM 2. concentratons (µg/m 3 ) Sant-Ancet PM 2. daly concentratons 4 PM2 Obs 40 PM2 local 3 PM2 transboundary 30 PM2 AURAMS July July July July July July July July 1999 Tros-Rveres PM 2. daly concentratons July July July July July July July July July July July July July July July July June June June June June June June June June June 2001 PM2 Obs PM2 local 12 June June June June June June June June June June June June June June June June June June June June July July July August August August 2001 PM2 transboundary PM2 AURAMS 29 July July July August August August 2001 Quebec Cty PM 2. daly concentratons 40 PM2 Obs 3 PM2 local PM2 transboundary 30 PM2 AURAMS July July July August August August 2001 Fgure 2 : Daly PM 2. concentratons durng the three epsodes. The measurements (lght blue columns) and the model values (blue lne) are shown. The local and transboundary contrbuton computed wth equaton (4) are also shown n green and red respectvely. At St. Ancet, the model values and the observatons agree qute well wth PM 2. peaks synchronzed, except perhaps on August 2001 where the model has the peak on the 3 rd whle the observatons are maxmum on the 2 nd. The model agrees qute well wth the observatons at Tros-Rveres as well. The local contrbuton s more mportant here than at St. Ancet. Ths s to be expected snce Tros-Rveres s downwnd of Montreal whch s a major local source of smog precursors. Surprsngly, durng the 19 June

4 maxmum, the transboundary component s barely above the local one. The meteorologcal analyss reveals that there was a strong southwesterly flow durng the evenng of June 19 whch caused an ozone exceedance that was due to transboundary flow. The reason why the transboundary sgnal s not so clear for PM 2. on that day may be that the peak concentraton s somewhat underpredcted due to a lack n the transport of pollutants wthn the model or too strong a deposton. Further east, n Quebec Cty, the agreement between the model values and the observatons s not as good. The exceedance of July s mssed; a peak concentraton s predcted on 17 June 2001 whle t occurred on June 1 and on June 19. The peak PM 2. concentratons observed on 2 August 2001 s predcted to happen one day earler. Modelled PM 2. concentratons were splt nto the three components accordng to equaton (4) and the local and transboundary parts can be seen on fgure 2. When the total modelled concentratons are hgh, the sgnal s qute clear and not ambguous : one of the two components domnates. Past and present weather patterns determne whch of the local sources or the remote transboundary sources domnate. A few specfc cases wll be examned n the next secton. Among all exceedances that occurred durng the modelled epsodes, two cases wll be shown wth more detals, one where the exceedance s due to local sources and a second where t s due to transboundary flow. All other cases were also analysed and there were generally a good agreement between the backtrajectory analyss and the model results..1 Case of July 31, 2001 On that day, ozone exceedances of the 8-hour runnng average were reported n the Montreal area ncludng at the St. Ancet ste. However, no PM 2. exceedances were reported. The followng fgure 3 shows the 48-hour backtrajectory of the ar mass arrvng n the Montreal area at a heght of 92 mb at 1800 UTC (2:00 PM local tme). The backtrajectory clearly ndcates that the ar mass s of local orgn and the exceedances are due to local sources. The followng table 1 shows the model results and the measurements for 2 stes, St. Ancet and West Montreal, ths latter ste beng n the western suburb of Montreal, about 40 km to the north-east of St. Ancet. Ths smple assessment of AURAMS doesn t show all strengths and weaknesses of the model n predctng PM 2. and the cause of the dsagreement, but s ntended to make the reader aware that complex ar qualty models such as AURAMS are very useful tools and that they are constantly evolvng.. EVALUATION OF THE TRANSBOUNDARY INFLUENCE ON DAYS WITH CWS EXCEEDANCES In the provnce of Quebec, the man source of local smog precursors s the Montreal regon wth ts hgh level of NO x emssons. The transboundary sources come from the ndustralzed southern Ontaro, the Amercan Mdwest and to a lesser extent the ndustralzed East from Washngton to Boston. The typcal weather pattern leadng to hgh ozone or PM 2. levels n Southern Quebec s stagnaton under a hgh pressure system to accumulate pollutants, followed by a southwesterly flow to carry the pollutants from the Great Lakes area and Montreal along the St. Lawrence valley up to Quebec Cty. Fgure 3 : 48-hour 92 mb backtrajectory (n red) for Montreal/St. Ancet endng at 1800 UTC on July 31, Each lne segment between the dots represent 6 hours. At the St. Ancet ste, both equatons () and (6) ndcate that the ozone exceedance s due to local sources n agreement wth the backtrajectory analyss. 4

5 TABLE 1. Model results and dagnoss of transboundary nfluence August 31, 2001, ozone St. Ancet West Montreal Observaton 73 ppb 90 ppb Model value 104 ppb 62 ppb Local contrbuton 63 ppb 21 ppb Transboundary contrbuton 4 ppb ppb Background 37 ppb 36 ppb Transboundary (eq )? No Yes Transboundary (eq 6)? No No It s noted also that the model overestmates ozone concentratons by about 30 ppb. On the other hand, equaton () ndcates a transboundary nfluence for the West Montreal ste. Model values between the 2 stes, whch are about 40 km apart, have a dfference of about 40 ppb. The reason s that the West Montreal ste s too close n term of model grd ponts to the hgh NO x emssons produced by the cty and s affected by NO x ttraton of ozone n the model but not n the real world. Ths s why at ths ste the model underestmates ozone concentratons and that the results from equaton () are not correct..2 Case of June 1, 2001 On that day, ozone exceedances were reported n the Montreal area ncludng the St. Ancet ste, and also at the Tros-Rveres and Quebec Cty stes. A PM 2. exceedance was also reported at the Tros- Rveres ste. Fgure 4 shows the backtrajectores arrvng at the 3 stes at 92 mb on June 1. The duraton of the backtrajectory s agan 48 hours, whch s suffcent to estmate f the ar mass comes from a source regon or not. The backtrajectores arrvng at Tros-Rveres and Quebec Cty come from a source regon coverng Toronto (Canada) and Buffalo (USA) regons. However, t does not appear that the backtrajectory arrvng n Montreal (St. Ancet) comes from a source regon, beng away from the major urban centres. The model results wll help to dagnose the transboundary nfluence n ths case. Fgure 4 : 48-hour 92 mb backtrajectory for the 3 stes endng at 1800 UTC on June 1, Each lne segment between the dots represent 6 hours. Table 2 presents the model results for ozone. Despte the fact that the ozone concentratons are agan slghtly overestmated, the model gves a clear sgnal that the local component s domnant for Tros-Rveres and Quebec Cty and that the transboundary component domnates for St. Ancet. As a result, the transboundary nfluence s confrmed by equatons () and (6) at St. Ancet. It should be concluded that the two other stes are not mostly transboundary nfluenced snce both equaton lead to dfferent results and that the local component clearly domnates. TABLE 2. Model results and dagnoss of transboundary nfluence June 1, 2001, ozone St. Ancet Tros- Rveres Quebec Cty Observaton 72 ppb 67 ppb 67 ppb Model value 83 ppb 81 ppb 81 ppb Local contrbuton 4 ppb 36 ppb 34 ppb Transboundary contrbuton 36 ppb 11 ppb 9 ppb Background 43 ppb 34 ppb 38 ppb Transboundary (eq )? Transboundary (eq 6)? Yes No No Yes Yes Yes Table 3 below presents the model results for the daly PM 2. exceedance at the Tros-Rveres ste. Smlarly to the ozone results above, the local component s domnant and the elevated concentratons value of 4 µg/m 3 make both

6 equatons () and (6) agree wth a non nfluence of transboundary flow. Ths concluson s renforced by the fact that no other PM montor reported exceedances of the Standards n the vcnty. TABLE 3. Model results and dagnoss of transboundary nfluence June 1, 2001, PM 2. Tros-Rveres Observaton 4 µg/m 3 Model value 38 µg/m 3 Local contrbuton 32 µg/m 3 Transboundary contrbuton µg/m 3 Background 1 µg/m 3 Transboundary (eq )? No Transboundary (eq 6)? No 6. CONCLUSION Ths study focussed on the daly exceedances of the Canada Wde Standard for ozone and PM 2. over Southern Quebec durng summertme. Three epsodes were smulated wth the AURAMS model for a total of 2 days. The PM module of the model was brefly evaluated and t appeared that the model can reproduce the PM 2. concentratons qute well n the Montreal and Tros-Rveres regons. The model was not as good n the Quebec Cty area whch s farther from major sources of PM 2. and ts precursors. There mght be a problem wth advecton and/or deposton of PM 2. n the model. Further analyss s needed. The modelled ozone and PM 2. concentratons were splt nto three components, the local, transboundary and background usng model runs obtaned by settng successvely to zero anthropogenc emssons wthn and outsde the jursdcton. The local and transboundary components were used to assess the transboundary nfluence durng CWS exceedances. By subtractng n turn the local and the transboundary component from the actual measurement and comparng aganst a threshold, the usefullness of ths two-crtera approach was demonstrated. In all cases, the model smulatons have to be compared to feld measurements to verfy f t can reproduce adequately the current stuaton, then the results must be compared wth other technques such as a backtrajectory analyss or the use of an upwnd montor as descrbed n the Gudance Document on Achevement Determnaton. The study hghlghted the fact that the model can predct the wrong result f the grd cannot represent adequately a gven ste. The measurement staton must be representatve of an area smlar to model resoluton. In ths study, the model resoluton was set to 21 km and t was seen that the West Montreal ste was not correctly represented by the model. 7. REFERENCES Bouchet, V. S., M. D. Moran,L.-P. Crever, A. P. Dastoor, S. L. Gong, W. Gong, P. A. Makar, S. Ménard, B. Pabla and L. Zhang, 2003 : Wntertme and summertme evaluaton of the regonalpm ar qualty model AURAMS. Proc 26 th NATO/CCMS ITM on Ar Polluton Modellng and ts Applcaton, May 26-29, 2003, Istanbul, Turkey. Canadan Councl of Mnsters of the Envronment, 2000 : Canada Wde Standards for Partculate Matter (PM) and Ozone. Avalable from e.pdf. Canadan Councl of Mnsters of the Envronment, 2002 : Gudance Document on Achevement Determnaton : Canada Wde Standards for Partculate Matter and Ozone. Report avalable from oct4.pdf, 6 pp. Côté, J., S. Gravel, A. Méthot, A. Patone, M. Roch and A. Stanforth, 1998 : The Operatonal CMC-MRB Global Envronmental Multscale (GEM) Model. Part I : Desgn Consderatons and Formulaton. Monthly Weather Revew, 126, Geron, C. D., A. B. Guenther and T. E. Perce, 1994 : An mproved model for estmatng emssons of volatle organc compounds from forest n the Eastern Unted States. Journal of Geophyscal Research, 99, Gong, S. L., L. A. Barre, J.-P. Blanchet, K. von Salzen, U. Lohmann, G. Lesns, L. Spacek, L. M. Zhang, E. Grard, H. Ln, R. Leatch, H. Leghton, P. Chylek and P. Huang, 2003 : Canadan Aerosol Module : A sze segregated smulaton of atmospherc aerosol processes for clmate and ar qualty models : Part 1. Module development. J. Geophys. Res., 108(D1), 4007, do: /2001jd002002, MacDonald, A. M., C. M. Banc, W. R. Leatch and K. J. Puckett, 1993 : Evaluaton of the Euleran Acd Deposton and Oxdant Model (ADOM) wth summer 1988 arcraft data. Atm. Env., 27A, Makar, P. A., V. S. Bouchet, L.-P. Crever, A. P. Dastoor, S. L. Gong, W. Gong, S. Ménard, M. D. Moran, B. Pabla, S. Venkatesh and L. Zhang, 2003a : AURAMS runs durng the Pacfc2001 tme perod a model/measurement comparson. Proc 26 th NATO/CCMS ITM on Ar Polluton Modellng and ts Applcaton, May 26-29, 2003, Istanbul, Turkey. Makar, P. A., V. S. Bouchet and A. Nenes, 2003b : Inorganc chemstry calculatons usng HETV a vectorzed solver for the SO NO NH 4 system based on the ISORROPIA algorthms. Atmos. Envron., 37, Moran, M. D., M. T. Scholtz, C. F. Slama, A. Dorkalam, A. Taylor, N. S. Tng, D. Daves, P. A. Makar and S. Venkatesh, An overvew of CEPS1.0 : Verson 1.0 of the Canadan Emssons Processng System for regonal-scale ar qualty models. Proc 7 th AWMA 6

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