Policy Analysis. Environmental Implications on the Oxygenation of Gasoline with Ethanol in the Metropolitan Area of Mexico City.

Transcription

1 Policy Anlysis Downloded vi on October 20, 2018 t 17:41:37 (UTC). See for options on how to legitimtely shre published rticles. Environmentl Implictions on the Oxygention of Gsoline with Ethnol in the Metropolitn Are of Mexico City I. SCHIFTER,* M. VERA, L. DIÄ AZ, E. GUZMAÄ N, F. RAMOS, AND E. LOÄ PEZ-SALINAS Subdirección de Proceso y Medio Ambiente, Instituto Mexicno del Petróleo, Eje Centrl L. Cárdens 152, México, D.F., CP Motor vehicle emission tests were performed on 12 inuse light duty vehicles, mde up of the most representtive emission control technologies in Mexico City: no ctlyst, oxidtive ctlyst, nd three wy ctlyst. Exhust regulted (CO, NO x, nd hydrocrbons) nd toxic (benzene, formldehyde, cetldehyde, nd 1,3-butdiene) emissions were evluted for MTBE (5 vol %)- nd ethnol (3, 6, nd 10 vol %)-gsoline blends. The most significnt overll emissions vritions derived from the use of 6 vol % ethnol (reltive to 5% MTBE bse gsoline) were 16% decrese in CO, 28% reduction in formldehyde, nd 80% increse in cetldehyde emissions. A 26% reduction in CO emissions from the oldest fleet (<MY 1991, without ctlytic converter), which represents bout 44% of the inuse light duty vehicles in Mexico city, cn be ttined when using 6 vol % ethnol-gsoline, without significnt vrition in hydrocrbons nd NO x emissions, when compred with 5% vol MTBE-gsoline. On the bsis of the emissions results, n estimtion of the chnge in the motor vehicle emissions of the metropolitn re of Mexico city ws clculted for the yer 2010 if ethnol were to be used insted of MTBE, nd the outcome ws considerble decrese in ll regulted nd toxic emissions, despite the growing motor vehicle popultion. * To whom correspondence should be ddressed. Phone: +52 (5) Fx: +52 (5) E-mil: ishifter@imp.mx. Introduction The use of oxygented gsoline is mndtory in the metropolitn re of Mexico City (MAMC) s control strtegy to reduce mbient CO concentrtions nd improve urbn ir qulity. Methyl tertiry-butyl ether (MTBE) hs been the most importnt oxygented compound blended in the two types of gsoline sold in the country (Regulr nd Premium), both provided by the stte owned oil compny. The impct of substitution of MTBE by ethnol hs not been evluted yet in Mexico, nd is not likely to be identicl to others countries. Tht is especilly true if one tkes into ccount the ltitude, ge distribution of the vehiculr fleet nd the previling motor nd emissions control technologies. The MAMC is closed vlley lrgely forced to contin the tmospheric contminnts generted by economic ctivities. This region is especilly sensitive to tmospheric contmintion owing to its topogrphic, climtic, nd urbn conditions. Being one of the most highly populted zones, onefifth of the Mexicn popultion lives in n re of pproximtely 2300 km 2. The University of Denver monitored the on-rod emissions using remote sensing techniques in the Mexico City in 1991 nd returned in the fll of 1994 nd revisited the sme sites surveyed before (1, 2). They found lrge drop (round 50%) tht occurred in CO nd hydrocrbons emissions. However, insufficient motor vehicle informtion ws vilble for the 1994 dt set to fully explin the lrge decrese. It should be noted however, tht those results ccount for emissions for only single mode of vehicle opertion nd therefore do not cover the full rnge of modes included in the Federl Test Procedure (FTP). In this pper, we present comprtive ssessment of the environmentl impct in the MAMC of four different fuel formultions nd three different fuel-injection/ctlystcontrol vehicle technologies to provide quntittive bsis for future policy ctions in controlling nd reducing environmentl pollutnt emissions from motor vehicles in the MAMC. The context of this problem is the nture of the pollution problem in the MAMC which is lso one of the lrgest urbn centers in the world. In the MAMC ozone levels, the most criticl pollutnt, surpss the Pollutnt Stndrd Index of the United Sttes most of the yer. Oxygented (5% vol MTBE) gsoline ws introduced in the MAMC in 1989, nd the use of oxygented gsoline becme mndtory for the MAMC, Gudljr, nd Monterrey, the lrgest urbn res in Mexico. In 1997 fuel reformultion, which included chnging composition nd physicl properties, ws implemented nd MTBE concentrtion ws set to mximl vlue of 7.5 vol % long with restrictions to the romtics, olefins, nd benzene content. Using representtive fleet of the MAMC, exhust regulted emissions (CO, NO x, nd hydrocrbons) were evluted for MTBE- nd ethnol-gsoline blends. Also, in this work we determined the emissions of toxic ir pollutnts which t present time re unregulted but pose risk for humn helth. The ozone forming potentil vlues of the hydrocrbons from the exhust composition were determined nd compred. Bckground Ethnol is commonly used s n oxygente for blending in Federl reformulted gsoline in the U.S. (3). Reuter et l. reported emissions from vehicles ccording to the Federl Test Procedure (4). They found reduction in CO, totl hydrocrbons (HC), nd benzene emissions with ll fuel oxygentes, including MTBE, compred to the nonoxygented fuels. The NO x emissions incresed for ll of the oxygentes, but the result ws sttisticlly significnt for the ethnol fuels. Acetldehyde emissions incresed for ethnolgsoline blends. The fleet verge CO benefit for the 7 test oxygente fuels ws -3.8%/wt % O 2. Knepper et l. (5) worked with group of seven MY vehicles selected for their high emission chrcteristics. The oxyfuel effects were tested with 3.65 wt % oxygen ethnol fuel nd 2.76 nd 2.54 wt % oxygen MTBE fuels. The emission levels vried gretly due to unstble ir/fuel rtio. The CO benefits re lrger thn observed in normlly operting vehicles, verging bout -9.7%/wt % oxygen. The HC emissions verging bout -9.4%/wt % oxygen nd NO x bout +9%. Tests conducted by the EPA (6, 7) on norml nd high emitting vehicles employed 20 fuels in 27 MY /es001177w CCC: $ Americn Chemicl Society VOL. 35, NO. 10, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY Published on Web 04/10/2001

2 TABLE 1. Technology of the MAMC Fleet nd Vehicles Employed in This Study MY %of LDGV fleet technology vehicles odometer employed (km) < crburtor electronic ignition no ctlytic converter crburtor electronic ignition oxidtive ctlyst no oxygen sensor electronic ignition close-loop control fuel injection TWC One vehicle of the indicted MY. norml emitters nd 12 MY high emitters. Both showed similr CO nd HC emission benefits, estimted to be in the rnge of 4 to 5% reduction in CO/wt % oxygen. The oxyfuel effects on NO x emissions re smll in ll cses. A lrge effect of S content on CO emissions ws noted by Myotte et l. (6) who found 13.8% reduction in the combined norml nd high emitting fleet, when S ws decresed from 324 to 112 ppm. Benson et l. (8) reported 13% CO, 16% HC, nd 9% NO reductions from low emitting fleet, when the fuel sulfur content ws decresed from 466 to 49 ppmw. Hood nd Frin (9) exmined the effects of oxygente nd Reid vpor pressure (RVP) on emissions from n 11 vehicle fleet MY t severl mbient tempertures. The fuel oxygentes included 10% ethnol, 15% MTBE, nd 17.1% ETBE. The fleet verge CO emission levels were bout 5, 7, nd 15 g/mi t F, respectively. The HC emissions were reduced by bout 3.5%/wt % oxygen except for the high oxygen fuel t 35 F. The NO emissions were generlly higher. No distinct emission benefit of one oxygente over the others ws identified. Most dynmometer studies report the effects of oxyfuels on pollutnt emissions other thn CO. An importnt effect of ll oxygente fuels is chieved through dilution. Adding 8-15 vol % oxygente to bse gsoline lowers the benzene concentrtion proportiontely. Since some emissions re unburned fuel components, the dilution effect directly lowers their levels. In this work, emission tests were performed on 12 in-use vehicles, which were obtined from owners in the MAMC fter being selected rndomly using Motor Vehicle ownership dtbse. Our fcilities re udited by the Instituto Ncionl de Ecologí, n environmentl federl institution. Tble 1 shows some chrcteristics of the MAMC fleet s well s the technologicl fmilies employed in the tests. Considering their emission control technologies nd for simplicity, these fleets will be referred to s no ctlyst [modelyer (MY) before 1990], oxidtive ctlyst (MY ), nd three-wy ctlyst (MY ). These vehicles represent the emission control technology found in lrge segment of the present MAMC vehicle fleet. Emissions from ll vehicles were considered s norml emitters using the criteri tht their exhust emissions re below twice the certifiction stndrds. Four gsoline smples were obtined nd tested by blending 3, 6, nd 10 vol % of ethnol nd 5 vol % of MTBE to the sme hydrocrbon bse stock (Tble 2). The MTBE blend is fully complying with the requirements for MAMC s gsoline regultion (10) indicted lso in Tble 2. The key differences between the fuels re the RVP nd oxygen content. The MAMC gsoline regultions limit the RVP to 7.8 psi in order to control evportive emissions of hydrocrbons. At present, the oxygen cp limit of 2.7 wt % in the MAMC regultions will restrict the mount of ethnol blended into gsoline to bout 7.7 vol %. The totl consumption of gsoline in the country for the yer 1999 ws 511 millions of brrels/dy (90% Regulr) of which 23% ws sold in the MAMC. Experimentl Methods Ech vehicle ws submitted to generl inspection nd only those tht needed minor repir were ccepted. Once the vehicle ws pproved for testing, n extensive procedure ws performed in order to minimize the fuel chngeover effects (11) nd lter the vehicle ws tested following the FTP-75 of the U.S. certifiction test procedure for light-duty gsoline vehicles (12). Vehicles were evluted on Clyton model ECE chssis dynmometer with direct-drive vrible-inerti flywheel system. Three smples of dilute exhust gs from the constnt volume-smpling system were collected during the FTP corresponding to the cold trnsient phse (bg 1), the hot stbilized phse (bg 2), nd the hot trnsient phse (bg 3). The exhust emissions smples were nlyzed for THC, NO x, nd CO in our lbortory, s prescribed by stndrd FTP certifiction. Composite emissions were verged over the entire test cycle. Tests were performed by duplicte but third test ws conducted on ech vehicle if the difference between emission levels in bckto-bck tests exceeded 8%. Quntittive hydrocrbon nlysis ws performed ccording to the procedures published elsewhere (13). Fuel economy vlues were clculted from crbon mss-blnce mesurements obtined on the vehicles during chssis dynmometer testing (s opposed to being in-use vlues). Clcultions for fuel economy followed the procedure published elsewhere (14). Two types of evportive losses were evluted in our fcilities: Diurnl nd "hot-sok evportive emissions. Diurnl emissions occur while the vehicle is not operting nd result from the dily vrition in mbient temperture. As the mbient temperture increses throughout the dy, some gsoline in the fuel tnk vporizes, nd some of the vpors escpe to the tmosphere through leks in the fuel system nd emissions control system. Hot sok emissions hve historiclly originted primrily from the vehicle s crburetor; they occur immeditely fter the vehicle engine is turned off when gsoline in the crburetor bowl vporizes due to the temperture increse of the crburetor. To perform both evlutions, the protocol followed the procedure published in ref 12. The comprtive ozone forming potentil for the fuels ws determined using the Crter mximum incrementl rectivity (MIR) scle. The scle pplies n individul rectivity vlue to ech nonmethne orgnic compound mesured in the exhust or evportive emissions from the motor vehicles (15). Results Regulted Exhust Emissions. The CO emissions vritions s function of ethnol concentrtion, which were grouped depending on vehicle s emission control technology, re shown in Figure 1. In the fleet without ctlytic converter, the ddition of ethnol brought bout considerble CO emissions decrese in comprison with the MTBE bsegsoline. For instnce, CO emissions dropped bout 27% more with 6% ethnol thn with the bse-gsoline. In the fleet with oxidtive ctlyst, similr CO emissions decresing tendency ws observed upon incresing ethnol concentrtion. Here, 39% decrese in CO emissions (in comprison with bse-gsoline) ws chieved with 10% ethnol. However, in the fleet equipped with three-wy ctlytic converter (TWC) ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 10, 2001

3 TABLE 2. Relevnt Properties of the Gsolines property MTBE ethnol (vol %) (vol %) federl regulted properties grvity, 20/4 C Reid vpor pressure, (lb/in. 2 ) mx distilltion ASTM, D-86 ( C) 10% evported % evported % evported end point sulfur, ppm romtics, (vol %) mx olefins, (vol %) mx benzene, (vol %) mx (RON+MON/2) oxygen, (vol %) MAMC,Gudljr,Monterrey. FIGURE 1. Effect of ethnol concentrtion nd vehicles emission control technology on CO emissions. there ws not ny significnt vrition in CO emissions in ll the ethnol concentrtion rnge (3-10%) tested. Fuel vpor pressure nd gsoline sulfur content ffect the CO nd HC emission levels of vehicles. Myotte et l. (6) reported 11.3% reduction in CO emissions in the combined norml nd high emitting fleet, when the fuel RVP ws reduced from 8.3 to 7.6.psi. A lrge effect of sulfur content on CO emissions ws noted by Myotte et l. (7) who found 13.8% reduction in CO emissions in the combined norml nd high emitting fleet, when fuel sulfur ws decresed from 324 to 112 ppm by weight. The Auto/Oil AQIRP study reported 13% CO, 16% HC, nd 9% NO reductions from 10 vehicle, MY 1989, low emitting fleet, when the fuel sulfur content ws decresed from 466 ppm by weight to 49 ppm. The effect of ethnol concentrtion on THC emissions is shown in Figure 2. In the vehicle fleet without ctlytic device, there is significnt increse in THC emissions when using 3% ethnol-contining gsoline, nd higher ethnol concentrtions resulted in mrginl decrese, bout 7% (for 10% ethnol) in comprison with the bse-gsoline. The fleet with oxidtive ctlyst showed grdul THC emissions decrese with incresing ethnol concentrtion. However nd similr to the CO emissions cse, the THC emissions did not decrese significntly in the TWC-equipped fleet, within the ethnol concentrtion rnge tested. Seprtely, the Office of Science nd Technology Policy completed the most comprehensive study regrding oxygented fuels, in 1997 (16). This report concluded tht the percentge reductions in CO nd THC emissions from the use of fuel oxygentes were found to be smller in the newer technology vehicles compred to older technology nd higher emitting vehicles. High-emitting vehicles (mlfunctioning or operting in fuel-rich mode) generlly lso hve lrger CO reduction benefits from oxyfuels. The behvior of NO x emissions upon different ethnol concentrtions is shown in Figure 3. For both the oxidtive ctlyst nd TWC vehicles there is tendency to generte more NO x s the concentrtion of ethnol increses. For 3 or 6% ethnol, the TWC-equipped fleet showed lmost no vrition in NO x emissions, in comprison with the bse gsoline. Fuel Economy, Diurnl, nd Hot-Sok Evportive Emissions. The effect of ethnol concentrtion on the evportive emissions (s g of THC/test) nd fuel economy for the three fleet-types is shown in Tble 3. A comprison of the hot-sok evportive emissions from the three fleets VOL. 35, NO. 10, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

4 FIGURE 2. Effect of ethnol concentrtion nd vehicles emission control technology on THC emissions. FIGURE 3. Effect of ethnol concentrtion nd vehicles emission control technology on NO x emissions. clerly shows considerble decrese relted to the dvncement of the vehicles technology. For instnce, the TWC fleet shows n verge of 5.5 nd 4.0 times less hot-sok emissions thn the no-ctlyst nd oxidtive ctlyst fleets, respectively. Due to the incorportion of fuel injection devices in this fleet, less open prts re exposed to the tmosphere, s opposed to the crburetor-equipped fleets. On the other hnd, the technologicl content of the fleets ffects to lesser extent the diurnl evportive emissions. In the three fleets, incresing ethnol concentrtions brought bout higher hot-sok emissions. Notwithstnding, the vrition of hot-sok emissions in the TWC fleet when using 3 nd 6% ethnol ws negligible in comprison with tht of the bse-gsoline. The effect of ethnol concentrtion on the diurnl evportive emissions ws not cler. When using 6% ethnol, the fuel economy vlues were 7, 2.5, nd 2% higher thn the bse-gsoline, for no-ctlyst, oxidtive ctlyst, nd TWC fleets, respectively. The environmentl stndrd for totl evportive emissions in new vehicles sold in Mexico is 2 g/test for light-duty vehicles. Running losses, not mesured in this work, re probbly modest t low RVP nd medium tempertures, but increse substntilly t high RVP nd high temperture. Toxic Emissions. Tble 4 shows the vrition of toxic emissions s function of ethnol concentrtion nd vehiculr emissions control technology. Clerly, the four toxic compounds: benzene 1,3-butdiene, formldehyde, nd cetldehyde hve been gretly diminished with the dvncement of vehicles technology. In fct, the substitution of oxidtive ctlyst by TWC brought bout 4 nd 6 times ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 10, 2001

5 TABLE 3. Fuel Economy nd Evportive Emissions (Diurnl nd hot-sok) s Function of Vehicles Technology nd Ethnol Concentrtion gsoline no ctlyst fleet oxidtive ctlyst fleet TWC fleet evportive emissions FE (g/test) (km/l) diurnl hot-sok evportive emissions FE (g/test) (km/l) diurnl hot-sok evportive emissions FE (g/test) (km/l) diurnl hot-sok 5% vol MTBE % vol ethnol % vol ethnol % vol ethnol FE: fuel economy. TABLE 4. Vrition in Toxic Emissions s Function of Vehicles Technology nd Ethnol Concentrtion no ctlyst fleet (mg/km) oxidtive ctlyst fleet (mg/km) TWC fleet (mg/km) gsoline Bz 1,3C 2-4 FrAld AcAld Bz 1,3C 2-4 FrAld AcAld Bz 1,3C 2-4 FrAld AcAld 5% vol MTBE % vol ethnol % vol ethnol % vol ethnol Bz, benzene; 1,3C 4 2-, 1,3-butdiene; FrAld, formldehyde; AcAld, cetldehyde. FIGURE 4. Specific rectivity towrd O 3 formtion s function of ethnol concentrtion nd vehicles emission control technology. verge lower benzene nd 1,3-butdiene emissions, respectively, for the ethnol-contining gsolines. Evidently from Tble 4, the use of different types of oxygentes nd oxygen levels in dvnced emission control technology fleet hs smll mss effects on ldehydes emissions. The most detrimentl effect of ethnol ws the considerble increse of cetldehyde emissions (80-104%), regrdless of the different emission control technology in the three fleets. Vehicle exhust emissions dt hve shown tht cetldehyde emissions cn increse by s much s 100% with the use of 2.0 wt % ethnol oxygented gsoline, prt of which undergoes photochemicl rections in the tmosphere to mke peroxycetyl nitrte (PAN) (17). Reuter et l. (4) reported tht benzene emissions re reduced by fuel oxygente. VOL. 35, NO. 10, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

6 FIGURE 5. Comprison of CO emissions vritions for the yers 1999 nd 2010 in the MAMC. FIGURE 6. Comprison of THC, NO x, nd evportive emissions vritions for the yers 1999 nd 2010 in the MAMC. However, in this work, benzene seems to increse mong the ethnol fuelled vehicles equipped with TWC. Benzene exhust emissions re dependent on fuel nd ctlyst type used in the vehicle, for tht reson individul vritions re present due to cr to cr technology nd lso fuel formultion mke comprison difficult. On the other hnd, ethnol decresed formldehyde emissions (bout 46-50%); prticulrly in the fleets with oxidtive ctlyst or TWC. 1, ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 10, 2001 Butdiene emissions decresed more in the fleet with oxidtive ctlyst thn in the TWC-equipped fleet. The reson of this might be the greter oxidizing efficiency of the oxidtive ctlyst, thn tht of the TWC. Most of the other emissions remined prcticlly without vrition. The 1,3-butdiene emissions re reduced but not significntly except for the ethnol fuel with the highest oxygente content. The formldehyde emissions hs been reported not chnge

7 FIGURE 7. Comprison of toxic emissions vritions for the yers 1999 nd 2010 in the MAMC. significntly, lthough most studies find MTBE increses formldehyde emissions (9). Bez et. l reported verge ir concentrtions of formldehyde nd cetldehyde for Mexico City of nd 0.11 ppbv, respectively (18). Specific Rectivity. The MIR represents the predicted impct of the respective constituent on urbn tmospheric ozone formtion, expressed s grms of ozone per grm of the constituent. Ozone forming potentil for specific fuel ws computed by incorporting the MIR vlues for ll constituents mesured in the exhust from prticulr fuel. Specific rectivity (SR) is mesure of how much ozone could be produced by unit mss of emissions nd is typiclly expressed s grm of O 3 per grm of nonmethne orgnic gses (NMOG). The potentil of emitted compounds to form O 3 from ethnol-contining gsoline is shown in Figure 4. For the fleet with oxidtive ctlyst, there is only mrginl decrese in the ozone formtion with 6 nd 10% ethnol. In the cse of the TWC-equipped fleet, however, the effect of dding 3-10% vol ethnol to the gsoline in the ozone formtion ws negligible. The Ntionl Reserch Council (NRC) found tht the ozone formtion potentil (s mesured with the Cliforni MIR scle) of exhust emissions from motor vehicles operting on ethnol-blended gsoline were lowersbut not significntly lowersthn from motor vehicles using MTBEblended gsoline. The NRC lso concluded tht the mss nd ozone formtion potentil (per mile) of evportive emissions from ethnol-blended gsoline were significntly higher, nd tht this increse would be detrimentl to ir qulity in terms of ozone (19). This ltter finding ws ttributed to n RVP increse of 1 psi from the ethnolcontining gsoline (19). The vilble dt on exhust nd evportive emissions from older vehicles show tht the smll benefit in exhust emissions due to the higher oxygen content is not sufficient to overcome the lrge increse in evportive emissions (19). The increse in evportive mss emissions from 1 psi increse in RVP is so substntil tht even considering the lower rectivity of evportive emissions, the resultnt ozone forming potentil significntly increses when exhust nd evportive emissions re combined (20). Discussion Turnover rte of the Mexicn vehicle fleet is considerbly longer thn in the U.S. (15 nd 4 yers, respectively). Additionlly, the incorportion of emission controls in new vehicles ws delyed in Mexico compred to those in the U.S.. Thus, older, less fuel-efficient nd more polluting vehicles still comprise lrge percentge of the current vehiculr fleet in the MAMC. Approximtely, 44% of the vehiculr fleet is not equipped with ctlytic converter since the introduction of these emission control systems did not occur until the MY 1991 for new vehicles. The contribution by ech vehicle type for the yer 1999 nd 2010 ws clculted. In the cse of the extrpoltion for 2010, the estimtion of the totl vehicle popultion for given clendr yer ws used. To determine nnul sles we consulted the historicl dt of the Mexicn Mnufcturers Assocition of Vehicles nd projected vehicle sles nnul growth rte of 4% for Scrppge is defined s the number of vehicles scrpped or otherwise removed from circultion in ny given yer, this vlue is reported s percentge of the number of vehicles in use. To determine the effects of nnul vehicle scrppge, we consulted rtes reported recently by the Inspection/Mintennce Progrm, mndtory twice per yer in the MAMC, of vehicles tht filed to obtin the permission to circulte. Higher rtes were pply to old vehicles but we estimted n verge scrppge rte of 2.7% nnully. The generl vehicle count formul is VCx ) (VCx Sles x) (1- SRx) (1) where VC is the vehicle count, SR is the percent of in-use fleet tht is scrpped, nd x is the current clendr yer. Figure 5 shows n estimtion of the totl emissions in ton per yer for CO for the yer 1999 nd extrpoltion to the VOL. 35, NO. 10, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

8 TABLE 5. Estimted Regulted Emissions Vrition CO THC thousnd (t/yr) NOx Evp 3% EtOH % EtOH % EtOH Difference in estimted totl fleet emissions for 2010 fleet (with ethnol gsoline) compred to tht of 1999 fleet (with MTBE bse gsoline). TABLE 6. Estimted Toxic Emissions Vrition benzene 1,3-butdiene (t/yr) FrAld AcAld 3% EtOH % EtOH % EtOH Difference in estimted totl fleet emissions for 2010 fleet (with ethnol gsoline) compred to tht of 1999 fleet (with MTBE bse gsoline). yer 2010 for the four fuels tested. Figure 6 shows similr results for THC, NO x, nd evportive emissions. These clcultions were crried out tking into ccount the verge dily trveled distnce nd the experimentl emission fctors clculted bsed on this study (see Supporting Informtion). The evportive emissions, s the pondered sum of diurnl nd hot-sok emissions divided by the dily distnce, re shown in Figure 6. For MY 2001 nd newer fleets, TIER-I emission fctors were used in the clcultions bsed on km certified emissions. From Figures 5-7 nd in spite of the motor vehicle popultion growth, it is cler tht ll emissions (regulted nd toxic) will be lower in the yer 2010 thn in the yer 1999, due to lower emissions fctors (of newer MY vehicles) nd disppernce of old highly polluting vehicles. There is considerble reduction trend in CO emissions s the ethnol concentrtion rise. THC emissions decresed bove 6 vol % ethnol. Nevertheless, NO x nd evportive hydrocrbon emissions incresed with ethnol concentrtion. A compromise between reduced CO emissions nd moderte NO x emissions could be ttined when using 6% ethnol gsoline. Clerly, ethnol incorportion in current gsolines should be ccompnied by more efficient ctlytic converter, prticulrly in its performnce on NO x reduction. Figure 7 shows the totl vritions in toxic emissions for the yer 1999 nd As discussed in previous sections, one of the clerest detrimentl effects of replcing MTBE for ethnol is the considerble increse in cetldehyde emissions. Totl formldehyde emissions would lso increse for the yer 2010 in the cse of the 10% ethnol gsoline. Lst, Tbles 5 nd 6 show the estimted regulted nd toxic emissions vrition, respectively, for the yer 2010 obtined with the ethnol ddition with respect to those of the 1999 MTBE bse gsoline. It is cler tht the mere substitution of MTBE for ethnol in Mexicn gsolines will not upgrde MAMC current ir qulity if it is not ccompnied by (1) ccelertion of old vehicles scrppge rtes (prticulrly those without ctlytic device), (2) improved ctlytic devices (to cope with toxic compounds), nd (3) imposition of new regultions on toxic emissions. The oxygente problem hs different scle in Mexico in comprison with tht in the U.S., s it is shown in Tble 7. The key differences in environmentl fctors re tht per cpit consumption of regulr nd oxygented gsoline is much lower in Mexico. Also, there re limited number of TABLE 7. Comprison of the Different Scles on the Oxygented Gsolines Issue in Mexico nd the U.S. highlights Mexico U.S. re of the country (km 2 /10 3 ) popultion (millions) gsoline consumption (brrels/dy10 3 ) 1998 oxygented gsoline, consumption (brrels/dy10 3 ) 1998 per cpit oxygented gsoline 2 12 consumption (brrels/dy10 3 ) significnt nturl wter reservoirs limited high round metropolitn res other consumption (Jet-skis,etc) limited moderte mount of vehicles (/10 6 ) vehicle verge ge (yr) 15 4 progrm to detect leks centrlized disperse wter bodies, round the mjor metropolitn res in Mexico in comprison with those in the U.S. The nonutomotive sources of contminnts re much lower in Mexico. But the most remrkble difference from Tble 7 is the vehicle verge ge: 15 yr in Mexico versus 4 yr in the U.S. Before ny ctions to remove MTBE from reformulted gsoline sold in Mexico s min metropolitn res were to be tken, studies to ssess MTBE content into groundwter re urgently needed. Groundwter contmintion hs been the key environmentl problem ssocited with MTBE-contining gsoline in the U.S., nd therefore, the potentil for groundwter contmintion in the MAMC should be considered relevnt fctor. The officil decision to bn MTBE, not lter thn December 31, 2002, from the gsoline sold in the stte of Cliforni (21), nd the recent nnouncement from U.S. EPA dministrtor to begin regultory ction imed t eliminting MTBE from gsoline nd boost ethnol use (22), serve s serious wrning tht soon MTBE will be bnned throughout the U.S., nd will probbly infiltrte into Mexico too. Current ethnol production in Mexico derives minly from sugr cne crops. If MTBE were to be bnned in Mexico, nd ethnol were to be the substituting oxygente, this could men gret opportunity to rescue the sugr cne industry nd vriety of renewble feedstocks. Supporting Informtion Avilble A more detiled description of the regulted nd toxic emission clcultions for the yers 1999 nd 2010 is vilble free of chrge vi the Internet t Literture Cited (1) Beton, S. P.; Bishop, G. A.; Stedmn, D. H. J. Air Wste Mnge. Assoc. 1992, 42, (2) Bishop, G. A.; Stedmn, D. H.; De l Grz Cstro, J.; Dvlos, F. J. Enivron. Sci. Technol. 1991, 31, (3) Howrd, C.; Russell, A.; Atkinson, R.; Clvert, J. Air Qulity Effects of the Winter Oxyfuel Progrm; White House Office of Science nd Technology Policy, Wshington, DC, July 2, (4) Reuter, R. M.; Gorse, R. A., Jr.; Pinter, L. J.; Benson, J. D.; Hochhuser, A. M.; Rippon, B. H.; Burns, V. R.; Koehl, W. J.; Rutherford, J. A. Auto/Oil Air Qulity Improvement Progrm; SAE Technicl Pper Series No , Society of Automotive Engineers, Wrrendle, PA, (5) Knepper, J. C.; Koehl, W. J.; Benson J. D.; Burns, V. R.; Gorse, R. A., Jr.; Hochhuser, A. M.; Lepprd, W. R.; Rpp, L. A.; Reuter, R. M. 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