Contributions of local and regional sources to fine PM in the megacity of Paris

Transcription

1 Atmos. Chem. Phys., 14, , 2014 do: /acp Author(s) CC Attrbuton 3.0 Lcense. Atmospherc Chemstry and Physcs Open Access Contrbutons of local and regonal sources to fne PM n the megacty of Pars K. Skyllakou 1,2, B. N. Murphy 3, A. G. Megarts 1,2, C. Fountouks 2, and S. N. Pands 1,2,4 1 Department of Chemcal Engneerng, Unversty of Patras, Patras, Greece 2 Insttute of Chemcal Engneerng Scences, Foundaton for Research and Technology Hellas (FORTH/ICE-HT), Patras, Greece 3 Department of Meteorology & Department of Appled Envronmental Scence, Stockholm Unversty, Stockholm, Sweden 4 Department of Chemcal Engneerng, Carnege Mellon Unversty, Pttsburgh, PA 15213, USA Correspondence to: S. N. Pands (spyros@chemeng.upatras.gr) Receved: 30 July 2013 Publshed n Atmos. Chem. Phys. Dscuss.: 8 October 2013 Revsed: 11 January 2014 Accepted: 21 January 2014 Publshed: 6 March 2014 Abstract. The partculate matter source apportonment technology (PSAT) s used together wth PMCAMx, a regonal chemcal transport model, to estmate how local emssons and pollutant transport affect prmary and secondary partculate matter mass concentraton levels n Pars. Durng the summer and the wnter perods examned, only 13 % of the PM 2.5 s predcted to be due to local Pars emssons, wth 36 % comng from md-range ( km from the center of the Pars) sources and 51 % from long range transport (more than 500 km from Pars). The local emssons contrbuton to smulated elemental carbon (EC) s sgnfcant, wth almost 60 % of the EC orgnatng from local sources durng both summer and wnter. Approxmately 50 % of the smulated fresh prmary organc aerosol (POA) orgnated from local sources and another 45 % from areas km from the receptor regon durng summer. Regonal sources domnated the secondary PM components. Durng summer more than 70 % of the smulated sulfate orgnated from SO 2 emtted more than 500 km away from the center of the Pars. Also more than 45 % of secondary organc aerosol (SOA) was due to the oxdaton of VOC precursors that were emtted km from the center of the Pars. The model smulates more contrbuton from long range secondary PM sources durng wnter because the tmescale for ts producton s longer due to the slower photochemcal actvty. PSAT results for contrbutons of local and regonal sources were compared wth observaton-based estmates from feld campagns that took place durng the MEGAPOLI project. PSAT smulatons are n general consstent (wthn 20 %) wth these estmates for OA and sulfate. The only excepton s that PSAT smulates hgher local EC contrbuton durng the summer compared to that estmated from observatons. 1 Introducton Fne partcles (PM 2.5 ) can cause a varety of problems to human health ncludng premature death (Dockery et al., 1993; Kunzl et al., 2000; Klemm et al., 2000; Pope et al., 2002). PM 2.5 s also responsble for vsblty reducton (Senfeld and Pands, 2006) and contrbutes to acd ran formaton (Burtraw et al., 2007) and clmate change by affectng the energy balance of our planet (Schwartz, 1996). One of the man challenges when tryng to mprove ar qualty n large urban areas s the quantfcaton of the contrbutons of local as well as long range pollutant transport. Identfyng the areas affectng the receptor s also a crucal ssue. A number of approaches have been proposed and used n order to estmate the role of local and regonal sources n dfferent areas. Three-dmensonal chemcal transport models (CTMs) can smulate all relevant atmospherc processes, so they have been used n several dfferent approaches. The smplest method s the so called zero-out analyss or bruteforce method (Park et al., 2003; Knppng et al., 2006; Chn et al., 2007; Koo et al., 2009) whch requres runnng the Publshed by Coperncus Publcatons on behalf of the European Geoscences Unon.

2 2344 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM correspondng CTM multple tmes by zerong out the emssons of a specfc source area or type. Ths s a computatonally expensve method because t requres multple smulatons, one for each source area of nterest. Another approach s the drect decoupled method (DDM) (Dunker et al., 1981) whch can provde local dervatves of the smulated pollutant levels to model parameters (such as emssons or process rate constants). DDM has been used to calculate the senstvty of the concentraton levels to changes n emssons. In general, DDM cannot be appled n large-scale perturbatons (Dunker et al., 2002). To overcome these problems, Yng and Kleeman (2006) developed the source-orented external mxture (SOEM) approach ntroducng addtonal speces for each source and trackng them separately throughout the model. In SOEM each secondary PM speces s traced back to ts precursors. For example the concentraton of partculate sulfate s traced back to SO 2 sources. Yng and Kleeman (2009) used SOEM to quantfy transport dstances n areas of Calforna. SOEM s accurate but computatonally demandng. Wagstrom et al. (2008) developed a computatonal effcent apportonment algorthm, the partculate source apportonment technology (PSAT) and used t for the frst tme n the Eastern Unted States (Wagstrom and Pands, 2011a) to estmate the contrbutons of emssons as a functon of dstance from the receptor for several urban and rural stes. PSAT s computatonally effcent as t works n parallel wth the man CTM wthout nterferng wth the CTM s calculatons. Koo et al. (2009) used PSAT to analyze concentratons from dfferent source regons and compared them wth the brute force method s results. They showed that DDM and PSAT can gve smlar results for pollutants that are related lnearly wth emssons but otherwse the results dffer because of the nonlnearty of the chemstry of secondary speces or other ndrect effects. In ths study we wll focus on the megacty of Pars. Ar qualty of Pars has been nvestgated through dfferent models such as CHIMERE (Zhang et al., 2013), PMCAMx (Fountouks et al., 2013), POLYPHEMUS (Royer et al., 2011), and H 2 O (Couvdat el al., 2013). Scare et al. (2010) compared SOA predctons of the regonal CTM, CHIMERE usng a sngle step oxdaton SOA scheme (Pun et al., 2006) aganst observaton-based estmates from the EC-tracer method (Turpn and Huntzcker, 1995; Strader et al., 1999; Cabada et al., 2004) at an urban ste. Fountouks et al. (2013) appled a fne grd nest over the megacty of Pars wth hgh resoluton (4 4 km 2 ). The evaluaton of the model aganst hgh tme-resoluton (AMS) measurements of fne partculate matter from three stes was encouragng. Zhang et al. (2013) mplemented the VBS approach nto CHIMERE to smulate the behavor of organc aerosol and compared wth measurements performed durng the MEGAPOLI summer campagn (Baklanov et al., 2010). Beekmann et al. (2014) used measurements nsde the center of the Pars and the surroundng areas to estmate what fracton of the partculate matter s local. The data were collected, durng July 2009 and January to md-february 2010 as a part of the MEGAPOLI ntensve feld campagns (Beekmann et al., 2014). PM 1 concentraton n Pars durng summer was on average between 5.3 and 7.5 µg m 3, but durng wnter was between 15.2 µg m 3 and 18.5 µg m 3. The same authors also estmated, based on the measurements n the approprate upwnd ste, that more than 70 % of PM 2.5 was transported nto Pars from areas far away from t. Durng more polluted perods (PM 2.5 > 40 µg m 3 at the urban ste), the regonal contrbuton was even larger (on average 80 %). In all, 70 % of the OA was found to be transported from regonal sources durng both summer and wnter. Freutel et al. (2013) found that the concentratons of secondary speces such as oxygenated OA, ntrate and ammonum durng the summer MEGAPOLI campagn were qute smlar for the three measurement stes n Pars, ndcatng the domnance of regonal transport. Sgnfcant levels of secondary speces were transported to Pars when the correspondng ar masses orgnated from contnental Europe. The mportance of the regonal sources n Pars was also confrmed by Crppa et al. (2013) for the wnter MEGAPOLI perod. The MEGAPOLI measurements provde a unque opportunty to compare the PSAT smulatons wth the estmated regonal contrbutons. In addton, PSAT can quantfy the average transport dstance from regonal sources to the Pars area, thus provdng addtonal nsghts. The orgnal verson of PSAT has been based on PMCAMx-2002, a CTM that assumes that prmary OA s non-volatle and nert and smulated SOA formaton usng the Odum et al. (1996) 2-product approach. Recent developments ncludng the sem-volatle POA and the contnuous agng of OA (Robnson et al., 2007; Lane et al., 2008; Shrvastava et al., 2008) have not been consdered n prevous source-receptor analyses by PSAT or other algorthms. In ths work we frst extend PSAT so that t can work wth the VBS approach (Donahue et al., 2006) for OA. We then apply the extended PSAT n PMCAMx-2008 n the European doman focusng on Pars for the frst tme. Ths paper descrbes the PSAT applcaton to the megacty of Pars for two dfferent seasons correspondng to the MEGAPOLI ntensve campagns. 2 Model descrpton 2.1 PMCAMx-2008 The model used n ths study s PMCAMx-2008 (Fountouks et al., 2011), a regonal three-dmensonal CTM. PMCAMx-2008 s appled to Europe, coverng a regon of km 2, usng 36 km 36 km grd resoluton and 10 vertcal layers extendng up to 6 km. The model s appled for two perods, 1 30 July 2009 and 10 January 9 February The gas-phase chemcal mechansm used s based on the SAPRC99 mechansm, ncludng 211 reactons of 56 Atmos. Chem. Phys., 14, , 2014

3 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM 2345 gases and 18 radcals. The PMCAMx SAPRC99 verson uses fve lumped alkanes, two olefns, two aromatcs, soprene, a lumped monoterpene speces, and a lumped sesquterpene speces. OA s treated n ths work as n Murphy and Pands (2010). Fountouks et al. (2011) evaluated the PMCAMx performance for the same European doman aganst ground measurements taken at four measurement statons and arborne measurements durng May The model reproduced more than 87 % of the hourly measurements of PM 1 OA and more than 94 % of the daly averaged OA concentratons wthn a factor of 2. Fountouks et al. (2013) nvestgated the role of grd nestng for ar qualty smulatons n Pars, by comparng the results of PMCAMx-2008 wth 4 km 4 km grd resoluton to those of lower resoluton (of 36 km 36 km) for the summer and wnter perod of the MEGAPOLI campagn. Fountouks et al. (2013) also evaluated the model aganst ground based measurements at the three MEGAPOLI stes of Pars. For the ste located n the center of the Pars (LHVP) the average smulated sulfate durng summer was wthn 0.2 µg m 3 of the measured value and the smulated EC was wthn 0.5 µg m 3. For the suburbs of Pars (SIRTA ste) durng summer, the model smulatons were also n agreement wth measurements of sulfate and OA components. EC was smulated to be lower than the measured concentraton, by less than 0.2 µg m PSAT descrpton The partculate source apportonment technology (PSAT) (Wagstrom et al., 2008) s an apportonment algorthm that can track dfferent pollutant categores orgnatng from dfferent area sources or dfferent source types. It s computatonally effcent as t works n parallel wth the man CTM wthout ncreasng the CTM s computatonal tme. PMCAMx-2008 communcates wth the apportonment algorthm after each step of each process (e.g., gas phase chemstry, horzontal and vertcal advecton, etc.) by sendng the correspondng concentratons of each speces calculated by the CTM s modules to the apportonment algorthm. After each process step of the man CTM, PSAT calculates the apportonment for each source and for each speces. The ntal condtons of the code are consdered as a separate source but ther effect decays rapdly durng the smulaton and becomes neglgble after a few days. The PSAT code requres a source-resolved nventory and matches the correspondng emssons wth the correspondng sources. PSAT uses the apportonment of the upwnd grd cell to apporton speces after transport calculatons nstead of trackng the source-specfc speces separately. Equaton (1) (Wagstrom et al., 2008) descrbes the apportonment of the newly formed speces A n a specfc grd cell : [ ] [ ] c A, (t) c A, (t) c A, (t + t) = c A, (t) + c n ca T (t) c out ca T (t), (1) where c A, (t) s the concentraton of speces A from source n a specfc cell at the begnnng of the correspondng tme step and c A, (t + t) s the same quantty at the end of the tme step, c n s the concentraton transported nto the grd cell, c out s the concentraton transported out of the grd cell, ca, s the concentraton of speces A from source n the upwnd grd cell and ca, T s the total concentraton of speces A from all sources n the upwnd grd cell. The apportonment of the newly formed secondary PM s calculated based on the apportonment of ts precursor speces. Ths means that the apportonment of each secondary PM speces s calculated by the same equatons as the apportonment of ts gas phase precursor. We have extended the orgnal PSAT algorthm of Wagstrom et al. (2008) to descrbe the OA mass based on the VBS approach (Donahue et al., 2006; Staner et al., 2008). Prmary OA emssons are dstrbuted nto dfferent classes of saturaton concentratons (volatlty bns). The correspondng gas-phase POA compounds can be oxdzed by the hydroxyl radcal leadng to products of lower volatlty. In the same way, SOA s consdered to be sem-volatle and can also be oxdzed further n the gas phase formng lower volatlty products. PSAT keeps track of the sources of all OA components (fresh prmary, oxdzed prmary, fresh and aged anthropogenc and bogenc secondary) usng the same approach used for all sem-volatle speces. All OA speces are dstrbuted nto dfferent volatlty bns and are tracked by PSAT as separate speces. OA speces are dstrbuted between the gas and the partcle phase accordng to Eq. (2) (Donahue et al., 2006): ξ = ( 1 + C C OA ) 1, (2) where ξ s the parttonng coeffcent of compound (fracton of compound n the partculate phase), C ts effectve saturaton concentraton and C OA s the total organc mass concentraton. Each C corresponds to a dfferent volatlty bn n the volatlty bass set. Chemcal agng reactons are assumed to shft the organc mass to the next lower volatlty bn correspondng to a reducton of the volatlty by one order of magntude. The apportonment of all sem-volatle secondary organc speces s treated as a reversble process and the apportonment of the newly formed OA, regardless of ts volatlty, s based on the apportonment of ts gas-phase VOC precursor. 2.3 Defnton of source regons wthn and around the Pars metropoltan area We have chosen nne computatonal cells to descrbe the Pars metropoltan area. We have also defned areas coverng dstances of approxmately 50 km, 500 km, and greater than 500 km away from the center of the Pars metropoltan area (Fg. 1) for the calculaton of the correspondng source contrbutons to PM levels. Atmos. Chem. Phys., 14, , 2014

4 2346 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM Fg. 2. Average smulated durnal profles of PM 2.5 components and ther sources for the summer perod for: (a) elemental carbon; (b) fresh POA; (c) sulfate and (d) SOA. Fg. 1. Defnton of dfferent source areas around Pars ndcatng local Pars emssons (black flled area), 500 km from the center of Pars (area nsde the black box not ncludng Pars) and > 500 km (area outsde the black box). PSAT also tracks the contrbutons to partcle concentratons from ntal condtons and boundary condtons. Concentratons resultng from emssons wthn Pars are consdered as local. The sum of the concentratons resultng from emssons outsde the Pars metropoltan area but wthn 500 km from the center of Pars s consdered as contrbuton of md-range transport and those resultng from emssons more than 500 km away from Pars (ncludng the effects of boundary condtons) are consdered as long range transport. The long range contrbuton therefore ncludes also the emssons outsde of the modelng doman. 3 Quantfcaton of source area contrbutons 3.1 Summer We wll focus frst on mass concentraton of three representatve major PM speces: elemental carbon, sulfate, and secondary organc aerosol. Elemental carbon s a non-reactve prmary speces, sulfate s secondary non-volatle, and SOA s a secondary sem-volatle speces. Fgure 2 depcts the smulated durnal pattern of EC, fresh POA, sulfate and SOA and the correspondng source areas. The EC concentraton peaks at 08:00 LT n the mornng. The concentraton of elemental carbon s on average 1 µg m 3. Durng the hours of the day wth the hgh concentratons the contrbuton of local transport s hgher. The contrbuton of Fg. 3. Percent contrbutons from each area durng hgh, all, and low partculate matter concentraton days for the smulated summer perod. local sources for EC s on average 64 % whle the contrbutons of md- and long range transport are 30 % and 6 % respectvely (Fg. 3). Ths behavor s characterstc of prmary pollutants wth sgnfcant urban sources (Wagstrom and Pands, 2011b). POA has almost the same behavor as EC wth a mornng peak at 07:00 LT n the mornng, but wth lower concentraton level than EC (on average less than 0.5 µg m 3 ). The behavor of sulfate s qute dfferent because t s a secondary speces. Average contrbutons of local, md-range transport and long range transport to sulfate n Pars are 6 %, 23 % and 71 %, respectvely (Fg. 3). Ths ndcates that sulfate n Pars s manly orgnatng from areas more than 500 km away from the cty. Ths s the result of the tme requred for ts formaton and the locaton of the major SO 2 sources. Smlarly to sulfate, less than 10 % of the SOA n Pars s smulated to be the result of local sources. SOA conssts of all the secondary compounds formed from reactons of evaporated POA, ntermedate volatlty organc compounds (IVOCs), and VOCs. SOA also ncludes the contrbuton of the boundary condtons for OA. Pars has modest VOC Atmos. Chem. Phys., 14, , 2014

5 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM 2347 Fg. 5. Smulated source area contrbutons to organcs (organc aerosol plus gas phase organc mass) n Pars as a functon of ther volatlty. Compounds wth effectve saturaton concentratons above 10 µg m 3 are manly n the gas phase, whle the rest are parttoned between the gas and partculate phases. Fg. 4. Percent contrbutons from each transport category (local, md-range and long-range) for dfferent types of organc aerosol durng the summer. Long range OA also ncludes the transported OA nto the doman. emssons compared to ts surroundngs and also several hours are requred for the formaton of SOA from freshly emtted VOCs. At the same tme VOC emssons orgnatng from Pars can be transported to other areas away from the cty and can be oxdzed there, formng sem-volatle oxdaton products whch can condense to form SOA. Md- and long range sources domnate contrbutng 45 % and 48 % respectvely of the SOA levels n the center of Pars. Fgure 3 summarzes the average smulated contrbuton from each source durng clean and polluted days. Clean days are defned as the days wth average concentratons of total PM 2.5 mass concentraton n the lower quartle of the values analyzed durng ths perod. Polluted days are defned as the days wth average total PM 2.5 concentratons n the upper quartle. Durng more polluted days 55 % of the EC s emtted by local sources wth another 37 % comng from md-range sources. On the other hand, durng clean days these contrbutons of EC are on average 63 % and 32 %, respectvely. The contrbutons of dfferent sources for sulfate and SOA do not change very much durng cleaner days compared to those of polluted days. It s noteworthy that PMCAMx/PSAT smulates that the relatve contrbuton of sources n Pars to total PM 2.5 tends to be lower durng polluted than durng average days. Ths rather surprsng result s consstent wth the observaton-based estmates of Beekmann et al. (2014) Organc aerosol sources A lttle more than 50 % of fresh POA n Pars s smulated to be the result of emssons from local sources accordng to PSAT, whle another 45 % s due to md-range transport and less than 5 % comes from areas more than 500 km away (Fg. 4). The POA contrbutons are smlar to those of the EC, but wth a lower local contrbuton due to the evaporaton of POA after emsson. Secondary organc aerosol precursors emtted far from Pars are oxdzed to form SOA whch s then transported to the megacty. Almost 50 % of anthropogenc SOA n Pars s smulated to be due to md-range transport and another 34 % due to long range transport. The behavor of bogenc SOA s qute smlar wth outsde sources contrbutng on average 83 % (Fg. 4). Total organc aerosol behaves lke SOA wth local emssons contrbutng on average 11 %, md-range transport 43 % and long range 46 % (Fg. 4). Long range transport domnates for total OA because the boundary condtons contrbute on average 30 % durng the summer. As the volatlty of organcs ncreases, the contrbuton of local sources s smulated to ncrease (Fg. 5). Organcs orgnatng from local sources are n general less oxdzed wth hgher volatltes, but organcs whch orgnate from long dstances are heavly oxdzed and typcally of lower volatlty. For the least volatle OA components n PMCAMx (effectve saturaton of 10 1 µg m 3 ), the contrbuton of local sources s smulated to be on average 10 % and the contrbuton of md- and long range transport s 62 % and 28 % respectvely. On the other hand for the more volatle OA components (effectve saturaton of 10 4 µg m 3 ), the contrbuton of local sources s 42 % and the contrbuton of md-range transport s on average 57 %. These hgh volatlty compounds are mostly n the gas phase Effects of Pars on other areas PSAT has the ablty to estmate the mpacts of a specfc source area, Pars n ths applcaton, on other areas and also the mpacts of the other specfed areas on the receptor regon. In order to quantfy how far from Pars the plume of each speces can travel, we can use a varety of metrcs (Wagstrom et al., 2011a). The transport dstance (TD) s a useful metrc of the average transport dstance. TD has been Atmos. Chem. Phys., 14, , 2014

6 2348 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM Fg. 6. Temporal varaton of the transport dstance for EC, sulfate and SOA at ground level for Pars emssons for the smulated summer perod. defned by Wagstrom et al. (2011b) as the dstance between the center of emssons and the center of the plume of the smulated concentratons at a gven tme. The coordnates of the centers ( ) ( ) X c,n,y c,n, Xe,n,Y e,n are calculated based on Eqs. (3) and (4) (Wagstrom et al., 2011a): ( Xc,n,Y c,n ) = X c,n, c,n Y c,n c,n (3) X e,n Y e,n ( ) Xe,n,Y e,n =,, (4) e,n e,n where c,n are the concentratons, e,n are the correspondng emssons of cell, n s the correspondng source area and X,Y are the coordnates of the cells of the correspondng concentratons and the emssons. For the calculaton of the TD of secondary speces lke sulfate and SOA, the coordnates of the emsson centers are calculated based on the emssons of ther precursor gases, SO 2 and VOCs, respectvely. Fgure 6 shows the temporal varaton of the smulated TD (from precursors emtted from the center of the Pars) durng the smulated summer perod, for EC, sulfate and SOA. The TD s qute varable because t depends strongly on meteorology. EC travels on average 400 km from Pars and ths TD s smulated to be lower than that of sulfate (600 km) and SOA (800 km). Fgure 7 shows the average mpacts of local Pars emssons of EC, SO 2 and VOCs on PM n areas far from Pars. Even f the plumes extend hundreds of klometers away from Pars, the absolute effects of ths megacty are modest (less than 0.1 µg m 3 for each PM 2.5 component) due to the relatvely low emssons of the urban regon. 3.2 Wnter The relatve source contrbutons durng wnter are qute smlar to those durng summer, despte the dfferences n absolute concentraton levels. Wnter s generally characterzed Fg. 7. Smulated average ground concentratons (n µg m 3 ) of PM 2.5 : (a) EC, (b) sulfate and (c) SOA orgnatng from the Pars area. Atmos. Chem. Phys., 14, , 2014

7 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM 2349 Fg. 8. Average durnal profles of PM 2.5 components and correspondng source areas for the wnter perod smulated for: (a) elemental carbon, (b) fresh POA, (c) sulfate, and (d) SOA. Fg. 9. Comparson of the contrbutons of each source area for the summer and wnter perods. by hgher emssons of EC and fresh POA and lower emssons of bogenc SOA precursors compared to summer (Table 1). Durng wnter the average smulated concentraton of EC n Pars was 2 µg m 3, whle durng summer t was 1 µg m 3. Also the dfference n concentratons between the two perods for fresh POA s sgnfcant. The smulated POA durng wnter s 1.5 µg m 3 and durng summer 0.2 µg m 3. The smulated durnal patterns of the concentratons and the correspondng source areas of EC, sulfate, fresh POA and SOA are shown n Fg. 8. The durnal average profles of EC and fresh POA are qute smlar, wth a mornng peak and reveal that durng the hours wth the maxmum concentraton levels, the contrbuton of local emssons s hgher. Durng wnter the concentratons of secondary speces such as sulfate and SOA are lower compared to summer because of the slower photochemstry. The durnal profle of sulfate s almost flat showng agan that local emssons do not play an mportant role. The seasonal changes n emssons, contrbute to the dfferences n relatve source contrbutons. These seasonal changes are summarzed n Table 1. However, ths effect s only part of the story as changes n transport patterns, resdence tme of local emssons over Pars, removal, photochemstry, etc., also affect the relatve contrbutons of the dfferent areas. EC durng wnter s characterzed by a lttle lower local Pars contrbutons and a lttle hgher transport from mdrange sources compared to summer (Fg. 9). The contrbuton of long range transport for sulfate s lower durng wnter due to lower regonal sulfate levels. Durng wnter the contrbutons of long range transport are lower, because PM components cannot travel long dstances as they are removed by ran. 4 Comparson of PSAT results and observaton-based estmates Beekmann et al. (2014) performed a detaled analyss of measurement data collected nsde and outsde Pars, n order to determne the role of local and regonal sources. They concluded that on an annual bass, 70 % of total PM 2.5 s transported nto Pars from areas far away from t. PSAT estmated (as the average of two perods) that 80 % s transported. Both the analyss of measurements and the PSAT smulatons suggest that more than 80 % of the sulfate s transported to Pars from other areas (Fg. 10). The two approaches are n excellent agreement durng the wnter, but PSAT analyzes a lower contrbuton of local emssons durng the summer. The dscrepancy s of the order of 0.2 µg m 3 and could be the result of underestmatng the effect of local sources, as PM- CAMx underpredcts the average sulfate n the center of the cty by the same amount (Fountouks et al., 2013) whle t s not based outsde Pars. Also the local smulated contrbutons of OA are lower than those estmated by observatons for both summer and wnter. Ths underestmaton of local sources (almost 0.2 µg m 3 for summer and wnter) could be explaned by the behavor of fresh POA. Both the measurement-based studes of Beekmann et al. (2014) and Freutel et al. (2013) found that almost 62 % of the OA n the center of Pars was HOA (Prmary Organc Aerosol) and cookng OA and 38 % was oxygenated OA. The dscrepancy between the measurements and the model can be explaned by the cookng emssons whch have not been ncluded n the PMCAMx nventory used n ths study. Cookng was estmated by Beekmann et al. (2014) to be a sgnfcant local source n Pars. On the other hand the local smulated contrbutons of EC are hgher than the measured especally durng summer but the absolute dscrepances are of the order of 0.2 µg m 3 for both summer and wnter. Healy et al. (2013) also calculated the local and transported PM nto the center of the Pars based on observatons Atmos. Chem. Phys., 14, , 2014

8 2350 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM Table 1. Emsson denstes for each source area durng the smulated summer and wnter perods. EC Fresh POA Anthropogenc SOA Bogenc SOA SO 2 (kg km 2 ) (kg km 2 ) precursors (kg km 2 ) precursors (kg km 2 ) (kg km 2 ) Summer Wnter Summer Wnter Summer Wnter Summer Wnter Summer Wnter Local Md-range Long range Fg. 10. Comparson of smulated and measured contrbutons of local and regonal sources for EC, sulfate and OA for the summer and wnter perods. durng January February PSAT predcts that durng the wnter perod the local contrbutons are 57 %, 17 % and 38 % for EC, sulfate and OA, respectvely, whle Healy et al. (2013) estmated these contrbutons to be 59 %, 16 % and 24 %, respectvely. Generally the predctons of the model are n a good agreement wth the estmates based on measurements and ths agreement s encouragng for both approaches. 5 Comparson wth other source-receptor analyss methods We also used PMCAMx-2008 (Fountouks et al., 2011) to analyze the contrbutons of each selected source area to PM n Pars by zerong out all the emssons (partcles and gases) from dfferent areas around Pars. These areas were selected to be the same wth those defned n PSAT smulatons. Two addtonal smulatons were performed: one zerong out the emssons of Pars (local emssons) and one zerong emssons orgnatng from areas that are outsde of Pars but less than 500 km away from t. An addtonal smulaton takng nto account only the boundary condtons was performed n order to calculate the mpacts of the boundary condtons on the concentraton levels consderng them as long range transport. The results of these were combned wth those of the base case smulaton. Fgure 11 compares the results of the two methods (brute force and PSAT) durng summer. There s good agreement between the two methods for both the prmary and secondary components. Ths agreement of Fg. 11. Smulated contrbutons of emssons from dfferent source areas to EC, sulfate and OA concentratons durng the summer n Pars for the zero-out approach and PSAT. the contrbutons of secondary speces s unexpectedly good gven the nonlnearty of the system. However, PSAT requres 5 tmes less CPU tme than the brute force method for these calculatons and s more accurate. 6 Conclusons In ths study we mplemented the PM source apportonment algorthm PSAT together wth the volatlty bass set framework for OA, n the megacty of Pars. Ths new verson of PSAT s used to quantfy the contrbutons from selected source areas to Pars fne PM mass concentratons for two perods, a summer and a wnter month. The contrbuton of local sources (wthn 50 km from the center of the Pars) was found to be around 60 % for EC durng both perods. On the other hand the concentratons of secondary PM components lke sulfate and SOA were domnated by long range and mdrange transport, respectvely. Long range transport was responsble for 71 % of the sulfate durng summer and 51 % durng wnter. For SOA durng summer the contrbutons of md- and long range transport were smlar (45 % and 48 % respectvely) whle durng wnter long range transport domnates (81 %). Durng more polluted days the contrbuton of regonal sources was smulated to ncrease slghtly for all PM speces. PSAT-smulated local contrbutons of EC are hgher than those estmated by the observaton-based method especally Atmos. Chem. Phys., 14, , 2014

9 K. Skyllakou et al.: Contrbutons of local and regonal sources to fne PM 2351 durng summer (wth local smulated beng 64 % and observaton based 33 %) ether ndcatng that the local emsson sources of EC n Pars have been overestmated or that the observaton-based approach s based low. On the other hand the comparson between the smulated contrbutons and those estmated based on measurements for sulfate s encouragng wth smulated transported contrbuton beng 94 % durng summer and 83 % durng wnter and the measured 81 % and 84 %, respectvely. Also OA mass was found to be transported nto Pars from regonal sources, on average 89 % durng summer and 62 % durng wnter and these results are relatvely consstent wth the observaton-based estmated values (80 % and 55 %, respectvely). The domnance of the contrbuton of regonal sources for secondary speces lke sulfate and SOA for the center of Pars s the result of the tme requred to convert precursors to PM speces. 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