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Nonregulated Pollutants Emitted from Euro 3 Diesel Vehicles as aFunction of Their Mileage

George Bikas , and Efthimios Zervas* ,

Institut fur Technische Mechanik, Templergraben 64, 52056 Aachen, Germany, and Department of EnV ironmental Engineering, Democritus Uni V ersity of Thrace, Vas. Sofias 12, 67100 Xanthi, Greece

Recei V ed January 22, 2007. Re V ised Manuscript Recei V ed May 23, 2007

The impact of mileage, from 4000 to 96 000 km, on the exhaust emissions of several nonregulated pollutantsis studied in the case of several Euro 3 diesel passenger cars, tested on the New European Driving Cycle. Theresults show that the emissions of the four regulated pollutants remain within the regulatory limits. ExhaustNO x and particulate matter remain constant with mileage, while the emissions of hydrocarbons and CO increase,because of a partial deactivation of the oxidation catalyst. Exhaust emissions of many nonregulated pollutantsare not particularly affected by the partial deactivation of the catalyst. Exhaust concentrations of methane,1,3-butadiene, benzene, the main carbonyl compounds, and particulate sulfates remain constant. However, theexhaust concentrations of some other nonregulated pollutants, such as exhaust olefins, heavy HCs, heavy carbonylcompounds, and light polycyclic aromatic hydrocarbons (PAHs) increase. The emissions of heavier PAHs andN2O decrease with mileage.

Introduction

CO, hydrocarbons (HCs), NO x, and particulate matter (PM)emissions of diesel passenger cars are regulated in terms of massemitted per distance driven on a regulated driving cycle. Drivingcycles have been derived to account for real life drivingconditions and are used for homologation purposes. Becausedriving conditions differ from country to country or betweencontinents, each region has its own driving cycles. The officialEuropean driving cycle is called New European Driving Cycle(NEDC), 1 but other cycles are used in the U.S.A. or Japan tocharacterize the local conditions. Each passenger car must

respect the exhaust emissions limits for a certain mileage,depending upon the regulation in use. In the European Union,the Euro 3 emission norm for passenger cars was introduced inthe year 2000 and was valid until the year 2005, when it wasreplaced by the more stringent Euro 4 regulation.

However, exhaust emissions also contain nonregulated pol-lutants, which are not subject of the introduced emission norms.Among diesel nonregulated pollutants, several authors study theemission of individual HCs 2- 4 and especially those of methane,a gas with a strong greenhouse effect. However, the totalcontribution of passenger cars to global methane emissions isestimated to be very low, not more than 0.3 - 0.4%5 of the totalmethane emissions.

N2O is a nonregulated exhaust pollutant with a very stronggreenhouse effect, which is about 300 times higher than this of CO2.6 Its lifetime in the atmosphere is estimated to be 170years.7 The contribution of passenger cars to total N 2O emissionsis estimated to 6 - 32% of the total N 2O emissions, dependingupon the author. 7- 9

Another family of diesel nonregulated pollutants is carbonylcompounds, which are emitted not only because of incompletecombustion but also because of the oxidation of HCs on theoxidation catalyst. Some authors study the emission of carbonylcompounds at some specific engine points 2,10 or on drivingcycles other than NEDC. 3,4,11 The first two carbonyl compounds,formaldehyde and acetaldehyde, are considered as toxic pol-lutants.

A particular family of pollutants is polycyclic aromatichydrocarbons (PAHs). PAHs are emitted in extremely lowconcentrations; however, some of them are suspected to be toxic.PAHs are also measured in the exhaust gas of diesel vehicles. 12It must be noted that the major part of PAHs is formed duringcombustion and not from fuel PAHs. 13

Even if several authors study the emission of the abovepollutants, there is no study today reporting the impact of vehiclemileage on their exhaust emissions. In this study, severalpassenger cars equipped with a Euro 3 diesel engine, are used

* To whom correspondence should be addressed. Telephone: + 30-24510-79392. E-mail: [email protected].

Institut fur Technische Mechanik. Present address: HMETC-Hyundai-Platz 1, 65428 Russelsheim, Ger-

many. Democritus University of Thrace.(1) Directive 70/220. www.europa.eu.int.(2) Zervas, E.; Montagne, X.; Lahaye, J. Atmos. En V iron. 2001 , 35,

1301 - 1306.(3) Schmitz, T.; Hassel, D.; Weber, F. J. Atmos. En V iron. 2000 , 34,

4639 - 4647.(4) Graham, L. Atmos. En V iron. 2005 , 39 , 2385 - 2398.(5) Nam, E. K.; Jensen, T. E.; Wallington, T. J. En V iron. Sci. Technol.

2004 , 38 , 2005 - 2010.

(6) Huai, T.; Durbin, T. D.; Miller, J. W.; Norbeck, J. M. Atmos. EnV

iron.2004 , 38 , 6621 - 6629.(7) Karlsson, H. L. Sci. Total En V iron. 2004 , 334 , 125- 132.(8) Becker, K. H.; Lorzer, J. C.; Kurtenback, R.; Wiesen, P. En V iron.

Sci. Technol. 1999 , 33 , 4134 - 4139.(9) Becker, K. H.; Lorzer, J. C.; Kurtenbach, R.; Wiesen, P.; Jensen, T.

E.; Wallington, T. J. Chemosphere: Global Change Sci. 2000 , 2 , 387-395.

(10) Cardone, M.; Prati, M. V.; Rocco, V.; Seggiani, M.; Senatore, A.;Avitolo, S. En V iron. Sci. Technol. 2002 , 36 , 4656 - 4662.

(11) De Abrantes, R.; De Assuncao, J. V.; Hrai, E. Y. ReV . Saude Publica2005 , 39 , 1- 6.

(12) Lin, Y. C.; Lee, W. J.; Wu, T. S.; Wang, C. T. Fuel 2006 , 85, 2516 -2523.

(13) Rhead, M. M.; Hardy, S. A. Fuel 2003 , 82 , 385- 393.

2731 Energy & Fuels 2007, 21, 2731- 2736

10.1021/ef070036d CCC: $37.00 2007 American Chemical SocietyPublished on Web 07/25/2007



to study the emissions of regulated and several nonregulatedpollutants, such as individual HCs, methane, carbonyl com-pounds, PAHs, N 2O, and sulfates, as a function of the mileage(or aging) from 4000 to 96 000 km.

Experimental Section

Two types of aging were used at this study. The first type wasbased on tests on the same vehicle, equipped with a Euro 3, 1.9 Ldiesel engine, at three different mileages. This passenger car wastested at 4000, 30 000, and 75 000 km. The second type of agingwas based on the analysis of different vehicles in use havingdifferent mileages, from 4000 to 96 000 km. All of these passengercars were equipped with the same Euro 3, 1.9 L diesel engine.

All passenger cars were tested on the NEDC using the officialEuropean regulations. 1 For the first vehicle, the analyzed pollutantswere regulated pollutants (CO, NO x, HCs, and PM) and nonregu-lated pollutants, such as individual HCs, carbonyl compounds,PAHs, N 2O, and particulate sulfates. The second type of aging (testson different passenger cars in use) was focused on the emissionsof the four regulated pollutants, methane, and N 2O.

The four regulated pollutants were analyzed according to theofficial European regulations. 1 Individual HCs were analyzed by

gas chromatography using flame ionization detector (GC/FID).Carbonyl compounds were collected in a 2,4-dinitrophenylhydrazine(DNPH) solution in acetonitrile, and the final solution was analyzedby high-performance liquid chromatography using ultraviolet detec-tion (HPLC/UV). N 2O was analyzed by gas chromatography usingelectron capture detection (GC/ECD). The soluble organic fraction(SOF) was extracted from PM, and PAHs were analyzed using high-performance liquid chromatography (HPLC) with fluorescencedetection, while particulate sulfates were analyzed using ionicchromatography (IC) with conductometric detection.

Results and Discussion

Emission of Regulated Pollutants. The emissions of regu-lated pollutants as a function of the mileage are shown in

Figure 1, where it can be seen that NO x and PM emissionsremain particularly constant with mileage. The results of thetests on the same vehicle at three different mileages show thatthis stability is observed not only on the NEDC but also on thetwo parts of this driving cycle, ECE (urban part) and EUDC(extra-urban part). The results of different vehicles with differentmileages show a quite remarkable stability of NO x emissions

because exhaust NO x emissions are on average 0.33 g/km (9.7%. Because NO x and PM are only engine-out pollutantemissions and there is no after-treatment to treat them, thisstatement indicates that engine aging does not have an effecton these emissions. Another author 12 reports than NO x emissionsdecrease at 18 000 km, while PM emissions remain constant,compared to the same vehicle at 0 km.

Contrary to NO x and PM emissions, HC and CO emissionsincrease about 40% from 4000 to 75 000 km in the case of thefirst vehicle; however, they remain within the regulatory limits.Lin et al.12 also reports an increase of these emissions from 0to 18 000 km. In our case, a higher increase is observed on theEUDC than the ECE: 40 and 30% increase in the case of HCs

and CO, respectively, in the case of the ECE, and 90 and 240%in the case of the EUDC. This is explained from a partialdeactivation of the oxidation catalyst at 75 000 km. In the caseof a fresh oxidation catalyst, even if engine-out HC and COemissions are higher on the EUDC than the ECE, a higherexhaust gas temperature of the EUDC helps to oxidize the majorparts of them. Consequently, a small deactivation of the catalystleads to a relatively higher increase of these emissions on theEUDC than the ECE. The above trends are also confirmed fromthe results of different vehicles.

Emission of Individual HCs. The exhaust of individual HCswas also analyzed. It must be noted that there is always adifference between the sum of all individual HCs measured by

Figure 1. Emissions of regulated pollutants as a function of the mileage for the same (in the case of NEDC, ECE, and EUDC) or different vehicles(in the case of NEDC) tested. PM emissions are not analyzed in the case of different passenger cars in use.

2732 Energy & Fuels, Vol. 21, No. 5, 2007 Bikas and Zer V as



acetaldehyde, acroleine, acetone, propionaldehyde, crotonalde-hyde, methacroleine, MEC plus butyraldehyde, benzaldehyde,n-valeraldehyde, m-toluenaldehyde, and hexanaldehyde, atexhaust concentrations from 0.02 to 12 mg/km. Isovaleralde-hyde, o-toluenaldehyde, and p-toluenaldehyde exhaust concen-trations were below detection limits.

The emission of the carbonyl compounds detected as afunction of the mileage is shown in Figure 6. Formaldehydeand acetaldehyde are the two major exhaust carbonyl com-pounds. 2,11 Figure 6 clearly shows that the emissions of lightercarbonyl compounds (formaldehyde, acetaldehyde, acroleine,acetone, and propionaldehyde) remain constant from 4000 to75 000 km. The exhaust concentrations of heavier carbonylcompounds, as crotonaldehyde, mathacroleine, MEC plus bu-tyraldehyde, benzaldehyde, n-valeraldehyde, m-toluenaldehyde,and hexanaldehyde, show an increase of 2 - 10 times, becauseof the partial deactivation of the oxidation catalyst. However,the exhaust concentration of these compounds on NEDC is quitelow, from 0.1 to 0.8 mg/km, in the case of 75 000 km.

The exhaust concentrations of all carbonyl compounds are

quite low at the EUDC (the exhaust concentration of most heavycarbonyl compounds are at the detection limits) and lower thanat the ECE. The increased exhaust temperature and thus thehigher performance of the oxidation catalyst is one reason forthat. On the other hand, the shifting of the operation pointstoward a higher speed and load during this driving mode causesa change in the level and distribution of the raw emissions, asthe combustion efficiency increases. The exhaust concentrationof almost all carbonyl compounds increases 40 - 50% at theEUDC with mileage because of the partial deactivation of theoxidation catalyst; however, this increase is very low comparedto the total emissions.

The percentage of each carbonyl compounds is shown inFigure 7. Formaldehyde is the major carbonyl compound; 2,11

its percentage is 51 - 56% on the NEDC. This percentage is

quite similar to the percentage reported in a previous study usingan older diesel engine operating on only one specific point, 2indicating that the mechanisms of carbonyl compound formationmust be quite independent of the engine technology. Generally,the formaldehyde percentage decreases very slightly withmileage and is slightly higher at the EUDC than the ECE.Acetaldehyde is the second carbonyl compound, 2,11 with apercentage corresponding to 25 - 30% of the total carbonyls onthe NEDC, following by acetone (7 - 10%), propionaldehyde(4%), MEC plus butyraldehdye (1 - 3%), benzaldehyde (0.7 -1.2%), methacroleine (0.3 - 1%), and crotonaldehyde (0.1 - 1%),while the other carbonyl compounds correspond to less than0.5% each. Except formaldehyde, there is no clear trendconcerning the percentages of carbonyl compounds at the EUDC

and ECE and their percentage as a function of the mileage.A previous study 11 reports that, for different vehicles testedon FTP, the ratio of formaldehyde/acetaldehyde always remainsconstant and around 7 / 3 or 2.33. In our case, the ratio of formaldehyde/acetaldehyde is from 1.7 to 2.8. The same studyreports 43 ( 34 mg/km of formaldehyde, 15 ( 13 mg/km of acetaldehyde, and 58 ( 47 mg/km of the total carbonylcompounds, however, using microbuses of older technologymeasured on the FTP driving cycle.

The exhaust concentration of the total carbonyl compoundscorresponds to about 20 - 40% of the total HC exhaust concen-tration (Figure 2). This percentage decreases with mileagebecause of the increased exhaust emissions of HCs as a resultof the partial deactivated oxidation catalyst. For the same reason,

Figure 4. (Lower curves) Exhaust emissions of CH 4 and N2O as afunction of the mileage, for different vehicles used (on the NEDC).(Upper curves) Exhaust emissions of N 2O and SO 42- as a function of the mileage, for one vehicle tested (on the NEDC, ECE, and EUDC).

Figure 5. Percentage of individual HCs over the total HCs as a functionof the mileage, at the NEDC, ECE, and EUDC.




this percentage is lower at the EUDC than the ECE. Thispercentage is quite similar to the percentage reported in aprevious study using an older diesel engine operating in onespecific point. 2 Another study 3 reports that carbonyl compoundscorrespond to 30 - 70% of the total HCs when older technologyvehicles were used on FTP and Autobahn driving cycles.

Emission of PAHs. The emissions of PAHs are shown inFigure 8. Because of technical reasons, no PAH analysis isperformed at the point of 30 000 km. It must be noted that themeasurement uncertainties are about 40% and most of thechanges presented here are within this variation. Total PAHemissions are quite independent of the mileage (8 g/km at 4000km and 9 g/km at 75 000 km). The exhaust concentrationsfound here are lower than the values reported in another study. 16Another author 12 reports that total PAH emissions decrease withthe mileage.

The main PAHs are fluoranthene (corresponding to about 29 -32% of the total PAHs), pyrene (about 18 - 24%), and benzo-(e)pyrene (about 11 - 12%). Figure 8 shows two tendencies aboutthe PAH concentration: that of heavier PAHs, which generallyremain constant or decrease with the mileage, and that of lighterPAHs, which increase. This last result is apparently due to theincreased difficulty of the oxidation of lighter PAHs on theoxidation catalyst because its partial deactivation leads to anincrease of their emissions. Heavier PAHs are more easilyoxidized, and a partial deactivation of the oxidation catalyst doesnot influence their emissions.

Emission of N 2O. The emissions of N 2O as a function of the mileage are shown in Figure 4. In the case of one vehicle,

the N2O emission is 16 g/km on the NEDC at 4000 km anddecreases with the mileage to reach 8 g/km at 75 000 km. Otherstudies, using American driving cycles, 8,9 also report similarvalues. N 2O emissions from vehicles of newer technology aregenerally lower. 17

N2O is formed on catalytic converters 6,7,17 and preferably atlow temperatures, where catalytic activity is low, and for thisreason, N 2O emissions are higher at a cold start than a hot start. 17For this reason, the N 2O emissions decrease as a function of the mileage because of the partial deactivation of the oxidationcatalyst. The emissions of N 2O using several vehicles confirmthis trend (lower curves in Figure 4). Because catalytic activityis higher on the EUDC than the ECE as a result of an increased

temperature, N 2O emissions should be lower at this part of thedriving cycle. However, the opposite trend is observed; N 2O ishigher on the EUDC than the ECE. This is apparently due tohigher NO x emissions of the EUDC. It must be noted that thereis no evident correlation between NO x and N2O emissions orbetween N 2O emissions and the temperature of the oxidationcatalyst.

Emission of Particulate Sulfates. The emissions of particu-late sulfates on the NEDC are very low, about 1.3 - 1.5 g/km(Figure 4), and remain constant as a function of the mileage,indicating that the partial oxidation of the catalyst does not

(16) Geller, M. D.; Ntziachristos, L.; Mamakos, A.; Samaras, Z.; Schmitz,D. A.; Froines, J. R.; Sioutas, C. Atmos. En V iron. 2006 , 40 , 6988 - 7004.

(17) Lipman, T. E.; Delucchi, M. A. Clim. Change 2002 , 53, 477-516.

Figure 6. Exhaust emissions of carbonyl compounds as a function of the mileage, at the NEDC, ECE, and EUDC.

Figure 7. Percentage of each carbonyl compound as a function of themileage, at the NEDC, ECE, and EUDC.

Pollutants Emitted from Euro 3 Diesel Vehicles Energy & Fuels, Vol. 21, No. 5, 2007 2735



influence them. The percentage of sulfates on the mass of collected particles is 3% (another author reports 2%) 18 andremains constant as a function of the mileage.

Conclusions

The emissions of regulated and several nonregulated pollut-ants are studied on the NEDC as a function of the mileage inthe case of passenger cars equipped with a Euro 3 diesel engine.Two types of tests were used. The first is based on tests on thesame vehicle, equipped with a Euro 3, 1.9 L diesel engine, at4000, 30 000, and 75 000 km. The second one is based on testsof different vehicles in use, all equipped with the same engineas the previous vehicle, having different mileages from 4000to 96 000 km. The target is to find out if some pollutants increasewith mileage.

The obtained results show that all four regulated pollutantsremain within the regulatory limits in the case of new and agedengines. Exhaust NO x and PM emissions remain particularlyconstant with the mileage, and the emissions of new or agedengines are quite similar. It must be noticed that there is noafter-treatment device for these two pollutants, and the agingof mechanical parts of the engine does not increase their exhaustemissions. Contrary to this, exhaust HC and CO emissionsincrease about 40% from 4000 to 75 000 km, because of thepartial deactivation of the oxidation catalyst at increasedmileages. The deactivation of the oxidation catalyst leads to anincrease of exhaust olefins and heavier HCs with mileage, whileexhaust emissions of methane, 1,3-butadiene, and benzene arenot influenced.

The partial deactivation of the exhaust catalyst leads to anincrease of some nonregulated pollutants, such as some heavierand minor carbonyl compounds and some light PAHs. However,exhaust emissions of the main exhaust carbonyl compounds andtotal PAHs remain constant with mileage. Because N 2O isformed on catalytic converters, its exhaust concentrationdecreases with mileage, as a result of the partial deactivationof the oxidation catalyst. The emissions of particulate sulfatesare very low and independent of engine and oxidation catalystaging.

EF070036D(18) Kirchstetter, T. W.; Harley, R. A.; Kreisberg, N. M.; Stolzenburg,

M. R.; Hering, S. V. Atmos. En V iron. 1999 , 33 , 2955 - 2968.

Figure 8. Exhaust emissions of PAHs as a function of the mileage, atthe NEDC.


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