Air Pollutant Emissions from a Four-Stroke Motorcycle Engine Influenced by Gasoline Aromatic Content

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1 Air Pollutnt Emissions from Four-Stroke Motorcycle Engine Influenced by Gsoline Aromtic Content Yungchen Yo #1, Jiunhorng Tsi *2, Anlin Chng *2 # Green Energy nd Environment Reserch Lbortories, Industril Technology Reserch Institute, 195 Sec. 4 Chung-Hsing Rd. Chutung, Hsinchu, 310, Tiwn, Republic of Chin * Deprtment of Environmentl Engineering nd Reserch Center for Climte Chnge nd Environmentl Qulity, Ntionl Cheng Kung University 1 University Rd. Tinn City, 701, Tiwn, Republic of Chin 1 ycyo@itri.org.tw; 2 jhtsi@mil.ncku.edu.tw Abstrct-Motorcycles re one of the dominnt sources of ir pollutnts in mny Asin countries. This focuses on the effect of fuel romtic content on motorcycle emissions. Two levels of romtic content test-fuels were designed to investigte the criteri pollutnt emissions [CO, totl hydrocrbons (THCs), nd NOx] nd gseous orgnic compounds in the exhust from non-ctlyst four-stroke motorcycle engine. All experiments were operted in cold strt mode. The dt indicte tht lowering romtic content in gsoline from 30 to 20% (by volume) reduced the CO nd THC emission by 8-17% nd 38%, respectively, especilly in the cruising test. The NOx emission, however, showed n inverse correltion with the romtic content in gsoline. Contrry to expecttions, the emission fctors of four orgnic groups nd ozone formtion potentil showed tht the low romtic fuel with highest emission fctors. While reduction of romtic content in gsoline my decrese emissions of benzene nd toluene, it will increse the emission of ldehyde. Since the percentge chnges of emission fctor of THC nd ir toxics in the motorcycle were lrger thn those in pssenger crs, the benefit of emission reduction due to fuel composition chnges in motorcycles my hve significnt impcts in helth risk nlysis. Keywords- Motorcycle; Aromtic Contents; Criteri Air Pollutnt; Orgnic Air Pollutnts; Ozone Formtion Potentil I. INTRODUCTION Motorcycles re populr on-rod vehicle in mny Asin urbn res nd they ccount for 50% to 70% of the totl vehicles due to the properties of high mobility, resonble price, nd low fuel-consumption. The popultion of motorcycles hs incresed by more thn 100% from 1986 to 2000, nd is still growing [1]. Therefore, developing nd implementing pollution control strtegies for emissions from motorcycles re criticl issue for chieving clen nd helthy ir in these countries. Motorcycles with cm 3 displcement re fr more populr thn hevy-duty motorcycles (displcement > 250 cm 3 ) in Tiwn nd other Asin countries. In Tiwn, motorcycle emissions contribute significnt prt of the ir pollutnt emission inventory; ccounts for 29% of CO, 8% of NOx, nd 22% of non-methne hydrocrbons [2]. The key fctors ffecting ir pollutnt emissions from vehicles re engine technology, driver behvior, fuel qulity, mong others [3-5]. Chnges in gsoline composition cn reduce vehicle emissions, becuse certin gsoline modifictions llow engine to perform t their optimum levels [6]. The effect of gsoline composition on vehicle exhust emissions hs been investigted since the erly 1990s. Two lrge-scle studies, the Air Qulity Improvement Reserch Progrm (AQIRP) by utomobile nd oil compnies in the United Sttes in 1989, nd the Europen Progrmme on Emission, Fuels, nd Engine Technologies (EPEFE) by the Europen Commission in 1992, were conducted to evlute the impcts of gsoline composition on exhust emissions nd ir qulity. Moreover, in order to understnd the effects of led-free nd reformulted gsoline on vehicle exhust emissions, severl studies hve been conducted using vrious vehicle modes (different model yer, new nd in-use, or pssenger crs nd light-duty trucks) to quntify their effects [7-10]. Bsed on the results obtined previously litertures, the romtic content of gsoline ffects exhust CO, THC nd some ir toxics emissions. AQIRP showed tht decrese of romtic contents in gsoline resulted in reductions in CO, [11, THCs (totl hydrocrbons), nd ir toxics emissions 12]. EPEFE progrm showed tht reducing romtics content decresed emissions of THC nd CO but incresed NOx nd yielded significnt effects on benzene emissions nd it ws liner reduction with decresing romtics. Formldehyde nd cetldehyde emissions lso showed incresing with romtics reduction. In contrst, reducing romtics my increse 1, 3-butdiene emissions [13]. Perry nd Gee (1995) [7] showed positive reltion between romtics content nd benzene emission nd lso effect on other ir toxics, such s ethylbenzene, toluene, nd m, p-xylene. Prti et l. (2000) [14] observed similr effect in two-stroke moped/motorcycle on benzene emission. Zervs et l. (2004) [15] hs reported the mjority of exhust benzene comes from fuel benzene, the two-thirds of toluene comes from fuel toluene, nd exhust ethylbenzene is minly produced from fuel ethylbenzene. However, no consistency between romtic content nd emission vrince hs been shown. Gsoline is complex mixture of 200 to 300 hydrocrbons nd its properties will differ depending on which of the vrious refining nd - 1 -

2 blending processes were used to mke it. This my contribute the different compositions of romtic compounds in gsoline, nd influence the ir pollutnt species of exhust. Moreover, lmost ll of the fuel-effect studies hve been conducted by using pssenger crs nd only rrely hve studies been focused on low engine cpcity (less thn 150 cm 3 [14, 16] ) motorcycle. With the different engine nd fuel supply systems, it is envisioned tht emissions from pssenger crs nd motorcycles re different. Furthermore, becuse motorcycles re used primrily s short distnce trvel tool nd the verge trvel speed is lower, there is corresponding increse in pollutnt emissions [5]. Consequently, informtion bout ir pollutnt emissions from motorcycles is of importnce. To the best of our knowledge, only one evluting effects of benzene nd romtics content in gsoline on criteri pollutnt nd benzene emissions for two-stroke motorcycles ws reported [17]. Unfortuntely, there re no dt concerning the effect in orgnic ir pollutnt emissions, nor other ir toxics informtion vilble. This ws undertken to evlute effects of romtic contents in gsoline on criteri ir pollutnt emissions (CO, THC, NOx), orgnic compounds [voltile orgnic compounds (VOCs) nd crbonyls], nd selected ir toxics from four-stroke motorcycle engine. Two levels of romtic content gsoline were prepred nd tested in the engine to investigte the effects of gsoline composition on the exhust gses in dynmometer. The ozone formtion potentil (OFP) of VOC smples of ech test fuel ws clculted to provide useful informtion relted to the potentil impct of different romtic content gsolines. The results of this will provide bsis for regultory gencies to pln n ir qulity control strtegy for fuel qulity in mobile sources. A. Test Fuels nd Engine II. EXPERIMENTAL DESIGN Two fuels (Fuels A nd B) were blended by the lrgest locl refinery in Tiwn; Fuel A presents the high romtic fuel (30 vol%) nd Fuel B ws the low romtic fuel (20 vol%). Ech fuel type contins two fuels nd treted s replicte. In ddition, the sulfur contents in fuel in most Asi Pcific countries re rnged from 50 to 500 ppm. The fuel sulfur ws controlled in 150 ppmw, this vlue presents the sulfur level in Minlnd Chin nd is reltively high s compred with the stndrd of Cliforni (30 ppmw for CRFG3) nd Europen Union (10 ppmw on 2003/17/EC). Anlysis of the test fuels ws crried out in the lbortory t the sme refinery compny. The ctul mesured vlues of the fuel compositions re presented in Tble I; the fuel compositions for commercil gsoline re lso included for comprison. A new four-stroke motorcycle engine with the displcement of 125 cm 3 ws chosen s the test one without ctlytic converters. The compression rtio of the engine ws 10.1:1. A crburetor ws used for the fuel supply system. TABLE I THE PROPERTIES OF THE STUDIES GASOLINE Fuel properties Fuel A Fuel B Sulfur (ppmw) Aromtics (vol %) Octne number Reid Vpor Pressure (kp) The listed vlues re the verge of two test fuels. B. Test Procedures Air pollutnt emissions re ffected by engine operting mode, becuse the combustion mechnism is different between idle nd cruising mode. Engine temperture is high while operted in cruising mode nd mking more complete combustion. Therefore, the mesured dt were evluted t two test modes, i.e., idle nd cruising mode, in the present. The motorcycle engine ws linked to the dynmometer nd tested t cold-strt mode under different rottion speeds, which were 1718±105 rpm, 4828±4 rpm, nd 5763±45 rpm for idle tests, mid-speed tests, nd high-speed tests, respectively. The ltter two rottion speeds were treted s cruising test mode. Prior to ech emission test, the engine ws soked in room temperture over six hours prior to the strt of the testing process. Exhust gses were connected to stinless chmber nd filter; criteri pollutnts were nlyzed simultneously by n in-situ monitor during 5-min operting time. The dt of pollutnt concentrtion nd engine speed were recorded every 5 sec by dt cquisition system. The verge vlue of 60 dt ws used s the ir pollutnt level. After ech test, the fuel tnk ws drined nd replced by one liter of new test fuel. Immeditely then, the engine ws kept operting for 5 min to flush fuel tnk nd pipes to prevent contmintion by the previous fuel. C. Gs Smpling nd Anlyticl Procedures CO, THC, nd NOx in the exhust filtered smples were mesured by n in-situ monitor (MEGA 300 Til Gs Anlyzer, Mstek Technologies). CO ws mesured by non-dispersive infrred nlyzer with detection rnge % nd with the resolution t 0.01%. THC ws monitored by flme ioniztion detection nlyzer with rnge of ppm (s propne, C 3 H 8 ) with 1ppm resolution. NOx (NO nd NO 2 ) ws monitored by chemiluminescence detection nlyzer with the detection rnge of ppm with 1 ppm resolution. Four tests of the commercil gsoline were conducted to evlute the test reproducibility. The verge vlues of reproducibility for CO, THC, nd NOx were 97, 92 nd 86% respectively for the idle mode nd 89, 84 nd 86% for the cruising mode. The exhust filtered smples were lso collected for ir toxics mesurements using smple bg (10 L) in vcuum smpling cse with the smpling flow rte of 150 ml/min. Air toxics species in the smple gs were quntified by gs - 2 -

3 chromtogrphy/mss spectrometer (Vrin Str 3600 GC plus with Vrin Sturn 2000 MS). The GC ws equipped with fused silic cpillry column (DB-1, 60 m 0.32 mm ID with 1.0 μm film thickness). Crbonyl components in the exhust were collected by silic gel crtridges with 2, 4- dinitrophenylhydrzine, nd extrcted with cetonitrile in the lbortory. The extrcts were nlyzed by high performnce liquid chromtogrphy (Hewlett Pckrd 1100 series) equipped with n ultrviolet-visible detector. The method detection limits for trget ir toxic pollutnts were 2.1 μg/m 3 (benzene), 3.8 μg/m 3 (1, 3-butdiene), 5.5 μg/m 3 (toluene), 9.7 μg/m 3 (formldehyde) nd 24.1 μg/m 3 (cetldehyde). Except for toluene, ll the selected ir toxics re crcinogenic. D. Clcultion of Emission Fctors nd Dte Anlysis The emission fctors of vrious pollutnts were ssessed with the exhust mss, the volume of the exhust, nd the fuel consumption in one test mode. The men rotting speed r (rpm) of the engine, the cylinder volume V motor (cm 3 ), nd the time t (min) over the test period were used to derive exhust volume, V (m 3 ) for specific driving mode. The mesured level (ppm or %) of pollutnt ws converted to the corresponding concentrtion W (g/nm 3 ) nd then the emission fctor of pollutnt, EF (g/l-fuel), ws clculted. The detil clcultion procedures re presented in our [5, 16] previous rticles. In ddition, the ozone formtion potentil (OFP) of VOC smples lso ws investigted using mximum increment rectivity (MIR). The OFP of certin VOC mixture in the exhust is clculted by summing up the concentrtions of mesured VOC nd corresponding MIR fctors. The scle [18] developed by Crter (2009) ws used to determine the MIR of the individul orgnic compounds. Since the MIR is populr method to ssess OFP, the detiled clcultion [5, 19] method cn be found in severl previous studies. III. RESULTS AND DISCUSSION A. Effects on Criteri Air Pollutnt Emissions 1) Idle Mode: The emission fctor (g/l-fuel) of fuel romtic contents on CO, THC, nd NOx emissions by motorcycle in the idle mode is illustrted in Tble II. Becuse the dt of THC were unstble during the idle test of Fuel B (high sulfur nd low romtic contents), the test results for tht low romtic content fuels were not nlyzed. The dt show tht decresing romtics in gsoline (from 30 to 20 vol%) decres exhust CO emissions by 8% nd 4% of CO (or 581 to 533 g/l-fuel). But effects of romtic content on CO showed no sttisticlly significnt (p = for CO). The low romtic content test fuel, however, showed higher NOx emission thn those with high romtic level nd the vrince is 14% (Tble II). The result of significnce nlysis, however, indictes no significnt effect (p = 0.619) on NOx from romtics content in gsoline. The observtions on the criteri emissions in the idle test show tht fuel romtic content reduction my lower the CO emission. This is in greement with the observtions from the previous studies for crs [8, 13, 20]. The previous cr studies further indicted tht reduction in fuel romtic content my increse NOx emissions s in our cse. Presumbly, it is ttributing to low ctlyst NOx conversion efficiency with low romtic fuels [13]. However, the sprk retrdtion due to high romtic content my reduce engine tempertures nd result in decreses in exhust NOx [21]. The sprk retrdtion seems to be the probble reson for low NOx emissions observed in the present. 2) Cruising mode: The emission fctors for motorcycle rnged from 184 to 220 g/l-fuel, 9.1 to 14.7 g/l-fuel, nd 3.6 to 6.4 g/l-fuel for CO, THC, nd NOx, respectively, in the cruising mode (Tble II). The test results indicted tht the CO nd THC emission fctors for test motorcycle were lower in the cruising mode thn those in the idle mode, except for NOx. The NOx emission in cruising mode, exhibiting one order of mgnitude higher thn those of the idle mode, is due to higher temperture becuse of high speed t the cruising mod e [22]. The observtions in Tble II showed tht reduction in romtic content (30 to 20 vol%) in the gsoline my led to lower CO nd THC emissions in the test motorcycle. The decresed percentge for CO emissions ws 17%, nd ws 38% for THC emissions (Tble II), but both without sttisticlly significnt impct (p = for CO, for THC). Reducing the romtics from 30 to 20 vol%, however, increses the NOx emission significntly (from 3.6 to 6.4 g/l-fuel or 76% increses), the p vlue ws The findings of the effects of gsoline romtic content on the CO nd THC emissions re in greement with the previous studies for crs [23-25]. Bsed on the resoning provided previously describing the idle test, the extended combustion-dely-period my result in low engine temperture nd low NOx emission for higher romtic content gsoline. Becuse the combustion temperture ws higher in cruising condition thn tht in the idle mode, the NOx emission ws incresed significntly, or from 0.5 to g/l-fuel. In conclusion, the present deduces tht reduction of gsoline romtic content, from 30 to 20 vol%, my decrese CO nd THC emissions from motorcycles, especilly in the cruising condition. In contrst, the NOx emissions were relted to fuel romtic content with n inverse correltion. TABLE II EMISSION FACTORS (G/L-FUEL) OF CRITERIA POLLUTANT IN DIFFERENT TEST FUELS Test fuel Aromtic content (vol %) EF t idle mode EF t cruising mode CO THC NOx CO THC NOx Fuel A Fuel B The dt of THC ws unstble during the idle test of Fuel B, the test results for tht low romtic content fuels were not nlyzed

4 B. Effects of Aromtic Content on Orgnic Compound Emissions The species of nlyzed orgnic ir pollutnts were divided into four groups: lknes (26 species), lkenes (10 species), romtics (16 species), nd crbonyls (15 species). Emission fctor of totl VOCs is the sum of four orgnic compound groups. Fig. 1 illustrtes the emission fctors (g/l-fuel) of totl VOCs nd four orgnic compound groups of four-stroke motorcycle exhust in two driving mode for vrious test fuels. The test results for tht low romtic content fuels (Fuel B) for the idle test were not nlyzed becuse the dt ws unstble. The emission fctors of totl VOCs were 10.5 g/l-fuel (Fuel A) in idle mode nd were 4.5 nd 9.1 g/l-fuel for Fuel A nd Fuel B, respectively. Contrry to expecttions, the low romtic fuel (Fuel B) showed higher VOCs emission thn Fuel A for the motorcycle engine in cruising mode. The emission fctor of four orgnic groups lso showed tht the Fuel B with highest emission fctors, especilly for lknes emission, the vlue is 4.3 g/l-fuel nd is 2.6 folds thn Fuel A. Redcting romtic content in gsoline will mke the other fuel composition (i.e. prffin, olefin) increse, this my contribute the high stright chin compound emissions. When compring the percentile of orgnic groups of Fuel A nd Fuel B in cruising mode, results indicted tht lknes group contributed the highest emissions in Fuel B (47%), but the percentile of other orgnic groups in Fuel A ws higher thn tht of Fuel B. The percentile ws 37/30/7% for Fuel A nd ws 31/19/4% for Fuel B in order of lkenes, romtics, nd crbonyls (Fig. 2). Fig. 2 Percentge contribution of four chemicl groups to the nlyzed VOCs for two romtic fuels (The percentge is clculted bsed on emission fctor per liter of fuel) C. Effects of Aromtic Content on Ozone Formtion Potentil Fig. 3 shows the OFP of motorcycle engine exhust fuelled with the two romtic fuels in cruising mode. The OFP in the high romtic fuel (27.6 g-o 3 /L-fuel) ws lower thn tht of the low romtic fuel (46.2 g-o 3 /L-fuel). The lkene chemicls showed the highest contribution of ozone formtion nd followed by romtic compounds regrdless of fuel types. Propylene, 1-butene, toluene, trns-2-butene, nd m, p-xylene were the mjor species reveled in the ozone formtion. The highest ozone formtion potentil ws propylene; the vlue ws 8.2 g-o 3 /L-fuel with contribution of 29% in Fuel A nd 14.3 g-o 3 /L-fuel with contribution of 31% in Fuel B. Results of ozone formtion potentil indicted the sequence of ozone formtion potentil ws lkenes > romtics > lkenes > crbonyls. () Idle mode (b) Cruising mode Fig. 1 Orgnic compound emissions fctors for the test fuels in different driving mode: () idle, (b) cruising Fig. 3 Ozone formtion potentils (g-o 3 /km) of motorcycle engine exhust in cruising mode for two romtic fuels In the view of vrince of OFP, the highest vrince ws ppered in lknes species while romtic level chnged from high to low; the vlue ws 225% or from 1.7 to 5.7 g- O3/L-fuel. The lkene chemicls lso showed high OFP vrince (which incresed by 68%, or from 17.6 to 29.6 g- O 3 /L-fuel). Slight decresing (2%) ppered in crbonyls - 4 -

5 while using low romtic fuel (Fuel B) s compred to the OFP of high romtic fuel (Fuel A). Formldehyde, cetldehyde, crolein, propion-ldeththyde, nd crotonldehyde were mjor crbonyl compounds tht cused ozone formtion from the motorcycle engine exhust for both test fuels. The top five species contributed 98% of the ozone formtion potentil in crbonyls. D. Effects of Aromtic Content on Orgnic Toxics Emission According to the results of previous cr studies, ir toxics were influenced by romtic contents in gsoline [7, 9, 10, 12]. Therefore, the effect of fuel composition on ir toxics ws concentrted on romtic contents in the present. Anlysis of fuel effects ws crried out by clculting the verge emission fctors of ir toxics for different romtic contents, nd the results re illustrted in Tble III. As would be expected, the concentrtions of most trget pollutnts, except for cetldehyde, were higher in the idle test thn those in the cruising test. Some of these compounds showed significnt reductions (Tble III) when chnging to the cruising mode, i.e. 1, 3-butdiend (98%), benzene (67-72%), formldehyde (42-43%) nd toluene (28-36%). During the idle mode, the engine, with higher ir/fuel rtio, produces higher hydrocrbon emission thn cruising mode. In contrst, the cruising mode my be stbilized with ner-stoichiometric ir/fuel rtio. Furthermore, engine rottion speed nd temperture were high during the cruising mode resulting in more complete [26] combustion. TABLE III AIR TOXICS EMISSIONS WHEN REDUCING FUEL AROMATICS CONTENT FROM 30 TO 20 VOL% AT IDLE AND CRUISING MODE Driving Mode Idle Cruising Air Toxics Emission Fctor (mg/lfuel) Aromtic 30 vol% Aromtic 20 vol% Vrition (%) Benzene ,3-Butdiene Toluene Formldehyde Acetldehyde Benzene ,3-Butdiene Toluene Formldehyde Acetldehyde Negtive differences (%) imply reductions in emissions while reducing romtic content in gsoline. In ll test fuels, toluene nd benzene represent the highest emissions mong the trget ir toxics. A decrese in romtic content from 30 to 20 vol% lowered toluene nd benzene emissions by 48% nd 17% in the idle test, nd 41% nd 30% in the cruising test, respectively. Goodfellow [13] et l. (1996) hs reported tht the incresed benzene nd toluene exhust emissions for higher romtic fuel re cused by delkyltion during the combustion process. As for 1, 3-butdiene nd formldehyde, the emission fctors showed similr results with low or high romtic fuel used. The 1, 3-butdiene results of motorcycle engine re in greement with pervious cr studies [7, 27]. However, 1, 3- butdiene is minly produced from olefins nd nphthene content nd is not influenced by romtics [27]. For cetldehyde, the dt, on the other hnd, show incresed emissions when low romtic fuel ws used. Acetldehyde is not present in the gsolines, it is the incomplete combustion products of fuel [6]. Decresing gsoline romtic content my require dditionl prffin content. The higher ldehyde emissions my be the result of the incresed frction of the prffin. Prtil combustion of prffin would result in n incresed formtion of methyl nd ethyl rdicls. These rdicls cn further undergo [20, 21] rections to form cetldehyde. Tble IV summrizes the effects of gsoline compositions on the motorcycle exhust emissions; dt for crs re lso included for comprison. Agin, the results indicte tht reducing fuel romtics contents my result in lower CO, THC, benzene nd toluene emissions. Benzene nd toluene were presented in gret mounts in motorcycle exhust, thus, ny step for reducing their emission should be tken. Although reduction of fuel romtics my increse ldehyde emissions, in terms of toxics emission control, low romtic content in gsoline my still contribute to n overll diminution in hzrdous risk. The fct tht reducing the romtic content in gsoline my lower the THC in generl nd ir toxics emission in prticulr which is lso observed in ctlyst free gsoline [7, 9, 17, 20] engine. Our findings re in ccordnce with the previous cr studies s shown in Tble IV. However, the percentge chnges of emission fctors in the motorcycle were lrger thn those in cr studies (typiclly less thn 10%). Becuse the emission fctors of motorcycles re quite higher thn those in crs; therefore, the benefit of emission reduction due to fuel composition chnges in motorcycles my hve significnt impcts in ir toxics. TABLE IV SUMMARY OF EFFECTS OF GASOLINE COMPOSITIONS ON THE VEHICLE EMISSIONS (A) CRITERIA POLLUTANTS Chnge in Test Engine Fuel Aromtics CO THC NOx Ref. New Four-Stroke Motorcycle, w/o Ctlyst (1) idle vol% b This NE (2) cruising vol% c This * In-Use Two-Stroke Motorcycles vol% [17] In-Use Crburetor Crs, w/o Ctlyst vol% [20] vol% [7] vol% * [9] Test Engine Chnge In Fuel Aromtics (B) AIR TOXICS Bz B d T ol New Four-Stroke Motorcycle, w/o Ctlyst N (1) idle vol% E N N (2) cruising vol% E E F A c Ref. This This - 5 -

6 In-Use Two-Stroke Motorcycles vol% [17] In-Use Crburetor Crs, w/o Ctlyst vol% * N E --- [20] vol% [7] vol% --- [9] Bz: benzene; Bd: 1, 3-butdiene; Tol: toluene; F: formldehyde; Ac: Acetldehyde b : increse; : reduction; NE: vrition less thn 5% in the present or no effect in other studies; ---: dt not mesured or not vilble c * significnt t the 95% confidence level IV. CONCLUSIONS This pper presents the correltion between fuel compositions nd ir pollutnt emissions (CO, THCs, NOx nd ir toxics) of non-ctlyst motorcycle engine. A fourstroke new motorcycle engine ws linked to the dynmometer nd operted in cold strt mode. The mesurement of emissions ws conducted during the idle nd the cruising test mode. The test fuels showing low emissions for CO nd THC were those tht hd consistently low romtic content, especilly in the cruising condition. In contrst, reducing romtic content from 30 to 20 vol% increses NOx emission in the test motorcycle. Contrry to expecttions, the low romtic fuel showed high totl VOCs emissions for the motorcycle engine in cruising mode. The emission fctors of four orgnic groups lso showed tht the low romtic fuel with highest emission fctors, especilly for lknes emission. The effects of romtic contents in gsoline re complex, probbly becuse the romtic compounds in gsoline re so diverse. The low romtic fuel lso hd the high ozone formtion potentil, propylene contributed the highest ozone formtion potentil mong ll nlyzed orgnic species. Results of ozone formtion potentil indicted the sequence of ozone formtion potentil ws lkenes > romtics > lkenes > crbonyls. For ir toxics emissions, reduction in fuel romtic content from 30 to 20 vol% decresed benzene nd toluene emissions in both test modes, but incresed the ldehyde emissions. Since the percentge chnges of emission fctors of ir toxics in the motorcycle were lrger thn those in crs, the benefit of emission reduction due to fuel composition chnges in motorcycles my hve significnt impcts in helth risk nlysis. According to our findings, in order to reduce the exhust THC nd ir toxics emissions, lower romtic gsoline is suggested. However, lower romtics in fuel my increse NOx, ozone formtion potentil, nd ldehyde emissions. ACKNOWLEDGMENT This reserch ws supported by grnts from the Ntionl Science Council nd the Environmentl Protection Administrtion, Excutive Yun, Republic of Chin (Tiwn) (NSC 94-EPA-Z nd NSC E MY3). REFERENCES [1] Asin Development Bnk (ADB), Policy guidelines for reducing vehicle emissions in Asi, Reducing Vehicle Emissions in Asi, Asin Development Bnk, Stock No , [2] Hndbook of Tiwn emission dt system (in Chinese), Tiwn Environment Protection Administrtion (TEPA), Tipei, [3] P. S. Pedersen, J. Ingwersen, T. Nielsen, E. 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