Combustion of Hydrotreated Vegetable Oil and Jatropha Methyl

Article pubs.acs.org/est

Combustion of Hydrotreated Vegetable Oil and Jatropha Methyl Ester in a Heavy Duty Engine: Emissions and Bacterial Mutagenicity Götz A. Westphal,*,† Jürgen Krahl,‡ Axel Munack,§ Nina Rosenkranz,† Olaf Schröder,§ Jens Schaak,§ Christoph Pabst,§ Thomas Brüning,† and Jürgen Bünger† †

Institute for Prevention and Occupational Medicine of the German Social Accident Insurance - Institute of the Ruhr-University Bochum (IPA), Bürkle-de-la-Camp-Platz 1, 44789 Bochum, Germany ‡ Coburg University of Applied Sciences and Arts, Friedrich-Streib-Strasse 2, 96450 Coburg, Germany § Thünen Institute of Agricultural Technology, Bundesallee 50, 38116 Braunschweig, Germany S Supporting Information *

ABSTRACT: Research on renewable fuels has to assess possible adverse health and ecological risks as well as conflicts with global food supply. This investigation compares the two newly developed biogenic diesel fuels hydrotreated vegetable oil (HVO) and jatropha methyl ester (JME) with fossil diesel fuel (DF) and rapeseed methyl ester (RME) for their emissions and bacterial mutagenic effects. Samples of exhaust constituents were compared after combustion in a Euro III heavy duty diesel engine. Regulated emissions were analyzed as well as particle size and number distributions, carbonyls, polycyclic aromatic hydrocarbons (PAHs), and bacterial mutagenicity of the exhausts. Combustion of RME and JME resulted in lower particulate matter (PM) compared to DF and HVO. Particle numbers were about 1 order of magnitude lower for RME and JME. However, nitrogen oxides (NOX) of RME and JME exceeded the Euro III limit value of 5.0 g/kWh, while HVO combustion produced the smallest amount of NOX. RME produced the lowest emissions of hydrocarbons (HC) and carbon monoxide (CO) followed by JME. Formaldehyde, acetaldehyde, acrolein, and several other carbonyls were found in the emissions of all investigated fuels. PAH emissions and mutagenicity of the exhausts were generally low, with HVO revealing the smallest number of mutations and lowest PAH emissions. Each fuel showed certain advantages or disadvantages. As proven before, both biodiesel fuels produced increased NOX emissions compared to DF. HVO showed significant toxicological advantages over all other fuels. Since jatropha oil is nonedible and grows in arid regions, JME may help to avoid conflicts with the food supply worldwide. Hydrogenated jatropha oil should now be investigated if it combines the benefits of both new fuels.

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INTRODUCTION

content, rapid growth, adaptation to wide agro-climatic conditions, and multiple uses of the plant as a whole.3 A recent study reported a general reduction in the global warming potential and the nonrenewable energy demand by use of Jatropha curcas biodiesel compared to fossil diesel. On the other hand, environmental impacts on acidification, ecotoxicity, eutrophication, and water depletion showed increases.4 We included jatropha methyl ester (JME) in this study as an alternative to RME, SME, and PME. Hydrotreated vegetable oil (HVO) was introduced to the market as a new alternative biogenic diesel fuel. HVO can be produced by the catalytic hydrogenation of plant oils. Its physicochemical properties are similar to petroleum derived diesel fuel (DF). Blends (mixtures) of DF and HVO did not result in elevated CO2 emissions or fuel consumption.5,6

The limited fossil oil resources urge the research for renewable fuels for the transport sector. Biodiesel (fatty acid methyl esters, FAME) was introduced to the market in the 1980s as a suitable alternative and was supposed to be environmentally friendly. Compared to petrol diesel fuel, the combustion of biodiesel results in a reduction of greenhouse gas emissions.1 Biodiesel is mainly produced by transesterification of rapeseed oil in Europe (rapeseed methyl ester, RME) and soybean oil in the USA (soy methyl ester, SME). In Asia, palm oil serves as the major source for biodiesel production (palm methyl ester, PME). Increasing research activities are focused on use of nonedible plant oils for biodiesel production, since the extensive use of edible vegetable oils raises concern due to the competition between fuel and food production resulting in rising prices of vegetable oils.1,2 Jatropha curcas has gained attention as a source for biodiesel production in tropical and subtropical countries and has spread beyond its center of origin, because of its hardiness, easy propagation, drought endurance, high oil © 2013 American Chemical Society

Received: Revised: Accepted: Published: 6038

February 4, 2013 May 2, 2013 May 6, 2013 May 6, 2013 dx.doi.org/10.1021/es400518d | Environ. Sci. Technol. 2013, 47, 6038−6046

Environmental Science & Technology

Article

and sulfur were identified as the crucial fuel components in this respect.28−32 Accordingly, early investigations in biodiesel exhaust revealed reduced mutagenicity of RME 33 and SME 34 compared to DF. These biofuels contain very low sulfur and aromatics. This advantage of biodiesel disappeared in more recent studies since sulfur and aromatics were strongly reduced in current DF qualities.9 Additives which increase the oxygen content of fuels can reduce the mutagenicity of engine emissions as well.35 Although most data indicate a reduction of DEE associated health risks from combustion of reformulated or new fuels, contrary effects can be observed as well. Pure rapeseed oil which is used as diesel biofuel in Germany and Austria increased the mutagenicity of DEE from a heavy duty engine strongly.9 So called blends, mixtures of biodiesel with common DF, caused enhanced mutagenic effects as well.36 These unforeseen results underline the importance of thorough investigations concerning the emission behavior of new fuels like HVO or JME. The present study compares the emissions of pure HVO, RME, JME, and DF following combustion in a Euro III heavy duty diesel engine. Besides the regulated exhaust components HC, NOX, CO, and PM, we investigated nonregulated emissions, especially particle number and size distribution, aldehydes, and PAHs. Adverse biological effects were investigated using the bacterial reverse mutation assay.

Moreover, a reduction of emissions of carbon monoxide (CO), total hydrocarbons (HC), and nitrogen oxides (NOX) was shown following combustion of a 30% blend with DF in a heavy duty engine.7 Combustion of blends in three different light duty vehicles yielded decreased CO, HC, and particulate matter (PM) emissions and reduced aldehydes, 1,3-butadiene, benzene, particle-bound polycyclic aromatic hydrocarbons (PAHs), and bacterial mutagenicity of the exhaust.5 In this study, we compared the emissions of 100% HVO with those of DF and two biodiesel fuels. The introduction of new fuels requires comprehensive investigation of possible hazards. This should involve ecological concerns and possible human health effects. The analyses of CO, HC, NOX, and PM are required by emission standards in the European Union, the U.S.A., and many other countries. Obviously the investigation of regulated exhaust components does not cover all suspected health effects of diesel engine emissions (DEE). Since studies on emissions and their biological effects after combustion of biofuels for diesel engines revealed unexpected results indicating increased health hazards,8,9 an intensified research on the possible hazards for human health is needed.10 Increased particle exposures are associated with acute and chronic respiratory diseases. These particle exposures are partly ascribed to DEE.11−15 Moreover, epidemiologic data point to adverse circulatory effects by particulate air pollution.16 DEE can also contribute to acute, adverse cardiovascular effects according to a controlled inhalation study with healthy volunteers and patients suffering from coronary heart disease.17 Long-term occupational DEE exposures were associated with an elevated lung cancer risk in a pooled analysis of 11 population-based European and Canadian case-control studies covering exposures from the 1950s to the 1980.18 Whereas most previous studies showed moderate increased lung cancer risks, a recent “nested case control study” revealed dosedependent increased odd ratios up to 7.30 (95% confidence interval (CI) = 1.46−36.57) for DEE exposed “non-metal miners” which were exposed toward 304 μg/m3-y or more.19 This investigation was based on a cohort study which included 12 315 workers exposed to DEE at eight US nonmetal mining facilities. Hazard ratios for lung cancer mortality up to 5.01 (95% CI = 1.97−12.76) were seen in this cohort.20 These results prompted the International Agency for Research on Cancer (IARC) to change the classification of DEE from “probably carcinogenic to humans” (group 2A) into “carcinogenic to humans” (group 1) in June 2012.21 Further evidence for the association of increased lung cancer mortality with DEE exposure was added by a recent retrospective cohort study on trucking industry workers using cumulative elemental carbon (EC) as a surrogate of exposure to engine exhaust from diesel vehicles, traffic, and loading dock operations.22 Carcinogenicity of DEE from combustion of common DF is ascribed to chronic inflammatory effects of diesel particulate matter and to PAHs which are adherent to the particles.1,23 Corresponding to the genotoxicity of many PAHs, extracts of diesel particulate matter induced strong mutagenicity in the bacterial reverse mutation assay.24,25 A small part of PAHs react with nitrogen oxides (NOX) out of the gaseous phase of DEE forming nitrated PAHs (nPAHs). Compared to their parent PAHs, most of the resulting compounds are much stronger mutagens and directly mutagenic.26,27 The mutagenicity of DEE mainly depends on the quality of the combusted fuels. A high content of aromatic compounds

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MATERIALS AND METHODS Study Engine and Engine Testing Conditions. We used a six cylinder, 6.37 L Mercedes-Benz OM 906 LA engine equipped with turbocharger and intercooler. The engine provides a maximum torque of 1100 N m at 1300 min−1 and complies with the EURO III emission standard. The crankshaft of the test engine was coupled with a controllable eddy-current brake (AG 250, Froude Hoffmann, Elze, Germany) enabling an automatic change to the different load modes of the ESC (European Stationary Cycle). The ESC (also known as OICA/ ACEA cycle) has been introduced for emission certification of heavy-duty diesel engines in Europe starting in the year 2000 (Directive 1999/96/EC of December 13, 1999). The ESC is a 13-mode, steady-state procedure that replaces the R-49 test. Particulate material for mutagenicity testing and characterization of particulate was sampled continuously with a constant sample flow of 25 L/min for 26 min from min 3 to min 28 during the ESC. For the analysis of regulated and nonregulated exhaust compounds, the cycles were run five times with each of the four fuels resulting in a total of 20 ESC cycles and three times for the bacterial reverse mutation assay resulting in 12 ESC cycles, respectively. Fuels. HVO (Trademark: NExBTL) was obtained from Neste Oil Ltd., Finland. JME was delivered by NTEC, National Metal and Materials Technology Center, Bangkok, Thailand. RME was purchased from ADM Hamburg AG, Germany. DF meeting the standard EN590 was delivered by Haltermann Products Dow Olefinverbund and GmbH, Hamburg, Germany. Fuel characteristics are listed in Table S1 of the Supporting Information. Regulated Emissions. CO, HC, and NO X were determined with a commercial gas analyzer and sampled each second. A mean was determined from the values sampled in the last minute of each operating point. The hot and filtered exhaust gas was passed to the HC analyzer via a pipe, which was heated to 190 °C. HC were analyzed by a gas analyzer (RS 556039

dx.doi.org/10.1021/es400518d | Environ. Sci. Technol. 2013, 47, 6038−6046


Article

T, Ratfisch Company, Poing, Germany) with flame ionization detector (FID). CO was analyzed via a BA-5000 gas analyzer (Bühler Technologies, Ratingen, Germany) and a “nondispersed infrared light” detector (NDIR). NOX were analyzed with a chemical luminescence detector (CLD 700 EL ht, EcoPhysics, München, Germany). PM was measured by use of a part-stream dilution tunnel. Dilution factors were calculated from separate recordings of CO2 contents in undiluted and diluted exhaust gas and fresh air. The dilution tunnel cooled down the exhaust stream below 51.7 °C. Particle mass was determined gravimetrically after sampling on PTFE-coated glass fiber filters (T60A20, diameter 70 mm, Pallflex Products Corp., Putnam, CT, U.S.A.), with sampling intervals according to individual weighting factors of each engine mode. Weights of fresh and sampled filters were determined to an accuracy of ±1 μg by means of a microbalance M5P (Sartorius, Göttingen, Germany) always preceded by 24 h of conditioning in a climate chamber held at 22 ± 1 °C and 45% ± 8% relative humidity. Particle Number and Size Distribution. All measurements were accomplished after dilution of raw exhaust gas in the dilution tunnel which was used for the determination of PM. A dilution factor of about 10 was applied for measurements with the Electrical Low Pressure Impactor (ELPI, Dekati, Tampere, Finland, aerodynamic diameter range 30 nm to 10 μm). The determination of the particle distribution took place after sampling with a multihole probe at the end of the exhaust gas dilution tunnel through a Scanning Mobility Particle Sizer (SMPS) System 3934 from the TSI Inc. St. Paul, USA, but a secondary dilution by factor 10 with an additional mixing pipe was required to avoid overloading of the measurement instrument. The particle size classes have an electrical mobility diameter of 10 to 300 nm. Aldehydes and Ketones. The raw exhaust was sampled at a flow rate of 0.5 L/min on silica coated DNPH-cartridges (2,4dinitrophenylhydrazine). The transfer tube was heated to 80 °C to avoid condensation. We used potassium iodine precolumns to minimize the reaction of the reactant hydrazones with nitrogen dioxide. The reacted hydrazones were injected in a volume of 10 μL onto a LiChrospher 100 RP-18 column (Merck, Darmstadt, Germany), which was kept at a constant 36 °C, and eluted with an acetonitrile/water gradient at a flow rate of 0.5 mL/min. The compounds were analyzed by HPLC-UV/ vis (370 nm). The following 13 standards were used for calibration: 2-butanone-DNPH, acetaldehyde-DNPH, acetoneDNPH, acrolein-DNPH, benzaldehyde-DNPH, crotonaldehyde-DNPH, formaldehyde-DNPH, hexaldehyde-DNPH, methacrolein-DNPH, m-tolualdehyde-DNPH, n-butyraldehyde-DNPH, propionaldehyde-DNPH, and valeraldehydeDNPH (Cerilliant, Round Rock, Texas, U.S.A) Polycyclic Aromatic Hydrocarbons. PAHs were analyzed from particulate matter and condensates. Particulate matter of each test cycle was collected from the raw exhaust onto PTFE (Teflon) coated glass fiber filters (T60 A20, Pallflex Products Corp., Putnam, CT, USA.). Prior to sampling, the filters were conditioned in a climate chamber (temperature 22 ± 1 °C; humidity 45% ± 8%) for 24 h in the dark, reweighted, and stored at −18 °C. PAH samples were taken from minute 3 to 28 of the ESC with a constant sampling flow of 25 L/min, according to VDI-Guideline 3872 part 1. The filters were conditioned (22 °C, rel. humidity 45%), weighed before and after sampling to determine the sampled particulate matter, and stored at −18 °C. The filters were extracted for 4 h with HPLC grade toluene using a fexIKA 50 extractor (IKA, Staufen,

Germany). The gas phase constituents were sampled as condensates by cooling the exhaust below 50 °C using an intensive cooler (Schott, Mainz, Germany). Remains in the cooler were desorbed with 100 mL of methanol. The condensates and the methanol desorbed remains were pooled and extracted three times for 5 min in an ultrasonic bath and with 30 mL of toluene/dichloromethane (1:1, HPLC grade). The extracts of the filters and condensates were stored at 4−8 °C. Extracts and condensates were reduced by rotary evaporation, dried under a stream of nitrogen, and redissolved in 4 mL of acetonitrile for further use. The PAHs in the extracts were separated and quantified using a HPLC with fluorescence detection (Elite LaChrom, VWR-Hitachi, VWR International GmbH, Darmstadt, Germany) by use of accumulation on a donor−acceptor complex chromatography (DACC) precolumn (ChromSpher Pi, Varian, Agilent Technologies Waldbronn, Germany) and an analytical Supelcosil LC-PAH column (Supelco, Sigma-Aldrich Chemie GmbH, Steinheim, Germany). An acetonitrile/water gradient was applied at a flow rate of 1.5 mL/min. Identification and quantification was done using a 16 PAH standard (LGC Promochem, Wesel, Germany) and an internal standard (para-quaterphenyl, Fluka, SigmaAldrich Chemie GmbH, Germany) which was added at the beginning of the extraction process. Bacterial Mutagenicity. Particulate matter and condensates of each ESC were collected from the undiluted exhaust as described above for the PAH analysis. Soxhlet filter extraction (Brand, Wertheim, Germany) of the soluble organic fraction was done with 150 mL of dichloromethane (Merck, Darmstadt, Germany) for 12 h in the dark (cycle time of 20 min at 65 °C). The particle extracts and condensates were concentrated by rotary evaporation (Heidolph, Kehlheim, Germany) and dried under a stream of nitrogen. Samples were stored at −18 °C and were redissolved in 4 mL of DMSO immediately before use.25 The soluble organic fraction (SOF) was determined by weighing of the conditioned filters before and after extraction with dichloromethane. The bacterial reverse mutation assay was performed according to the standard test protocol with Salmonella typhimurium tester strains TA98 and TA100.37 These strains were shown to be particular sensitive to mutagens in organic extracts of diesel engine particles.24 Extracts and condensates were tested in the following log 2 dilutions: 1.0, 0.5, 0.25, and 0.125. Each concentration was tested both with and without 4% S9 mix. Every extract and condensate was tested in triplicate. Plates were incubated at 37 °C for 48 h in the dark, and the revertant colonies on the plates were counted using an electronically supported colony counting system (Cardinal, Perceptive Instruments, Haverhill, Great Britain). The bacterial background lawn was regularly checked by microscopy, as high doses of the extracts proved toxic to the tester strains, resulting in a thinning out of the background. Methyl methanesulfonate (10 μg/mL in water), 2-aminofluorene (100 μg/mL in DMSO), and 3-nitrobenzanthrone (1 μg/mL in DMSO) served as positive controls (see Supporting Information, Table S2). Acceptance criteria for a positive test were positive and negative controls within the range of the historical controls and a reproducible, dose-dependent increase of reverse mutations across at least two consecutive concentrations.38 6040



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Figure 1. NOX emissions from combustion of DF, JME, HVO, and RME referred to provided energy [g/kWh]. The heavy horizontal line shows the European threshold limit value of 5 g NOX/KWh. Results are displayed as means with standard deviations.

Figure 2. PM emissions from combustion of DF, JME, HVO, and RME referred to provided energy [g/kWh]. Results are displayed as means with standard deviations.

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RESULTS Regulated Emissions. HC and CO emissions of all fuels were far below the EURO III limits (0.66 g/kWh and 2.1 g/ kWh). RME yielded the lowest HC and CO emissions, followed by JME, whereas DF and HVO showed about the same emission levels (see Figures S1 and S2 in the Supporting Information). NOX emissions of RME and JME exceeded the Euro III limit of 5.0 g/kWh. DF was just below the Euro III limit, whereas HVO clearly fell below the EU III threshold limit value by approximately 20% (Figure 1). Particle emissions of all fuels complied with the EURO III emission standard. Combustion of the methyl esters yielded about 35% and HVO 8% less PM compared to DF (Figure 2). Nonregulated Exhaust Constituents. SMPS analysis revealed lower ultrafine particle numbers for JME and RME up to 1 order of magnitude for particle sizes from 20 to 300 nm (Figure 3). Particle numbers of HVO were nearly identical to particle numbers of DF. These results were confirmed by ELPI measurements for ultrafine and fine particles up to 2410 nm (Figure 4). The lower emissions of JME and RME were observed across the whole particle size range. Formaldehyde, acetaldehyde, and acrolein were the predominant carbonyls in DEE of all investigated fuels. The results did

Figure 3. SMPS analysis of particle numbers and size distributions from exhaust of DF, JME, HVO, and RME referred to provided energy [1/kWh].

not differ significantly among the tested fuels for these three compounds in the Mann−Whitney U test. Other aldehydes and ketones were found in smaller amounts close to the detection limit. A nonsignificant trend toward higher carbonyl emissions 6041



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Figure 6. Emissions of PAHs [ng/ESC test] from combustion of DF, JME, HVO, and RME measured in filter extracts. Below the heavy horizontal line, the masses for the eight compounds on the right-hand side are shown multiplied by 10. Results are displayed as means with standard deviations. Abbreviations: see Figure 7.

Figure 4. ELPI analysis of particle numbers and size distributions from exhaust of DF, JME, HVO, and RME referred to provided energy [1/ kWh].

was seen following combustion of HVO and RME compared to JME and DF (Figure 5). PAHs occurred in small masses. Especially those PAHs which are composed of more than three rings (in Figures 6 and 7, the eight compounds on the right-hand side, below the heavy horizontal line) were detected only in very small amounts and even close to the detection limit in the condensates (Figure 7). DF produced the highest emissions of the analyzed 16 EPAPAHs, significantly higher for naphthalene (only condensates), fluorene, phenanthrene (only filter extracts), and pyrene in the Mann−Whitney U test. Only PAHs, which occurred in minor amounts, such as benz[a]anthracene and chrysene were seen in similar concentrations in the other exhausts. Among the PAHs with three and more rings, benz[a]anthracene, chrysene, and benzo[a]pyrene were found in greater masses in DF- and RMEfilter extracts. Benz[a]anthracene and chrysene were the only “high molecular mass” PAHs which were found in noteworthy amounts in the condensates of JME and RME. Combustion of HVO yielded the lowest PAH emissions, likewise in particle extracts and condensates (Figures 6 and 7). Soxhlet extraction of the filters sampled for the bacterial reverse mutation assay from the undiluted exhaust revealed a lower insoluble fraction (soot) of the particle mass for JME and

RME compared to HVO and DF, while the soluble proportion (mainly unburned fuel) was higher (Figure 8). Mutagenicity is displayed in revertants (mutations) per test or cycle, respectively. Mutagenicity is therefore automatically adjusted for differences in mass emissions output. All exhausts induced bacterial mutagenicity in both tester strains (Figures 9 and 10). Mutagenicity was stronger without addition of S9-mix and stronger in the particle extracts compared to the condensates. The strongest mutagenicity was induced by JME and RME. Only very weak mutagenic effects were observed after combustion of HVO.

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DISCUSSION This study compared exhaust compounds and their biological effects from combustion of HVO and JME, two new renewable fuels, with emissions of conventional DF and a common biodiesel quality, namely, RME. From the toxicological point of view, HVO showed up as a promising fuel in earlier investigations due to low emissions of PAHs and NOX. JME may have socio-ecological advantages, but toxicological data are lacking up to now.

Figure 5. Specific carbonyl emissions from combustion of DF, JME, HVO, and RME referred to provided energy [mg/kWh]. Results are displayed as means with standard deviations. 6042



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are more effective at lowering CO and HC than HVO, but both fuels produce higher NOX emissions exceeding the Euro III standard. Higher NOX emissions than DF seem to be a general feature of FAME.41 Therefore, hydrogenation may serve as a superior refinery for vegetable oils concerning NOX in DEE. On the other hand, PM is strongly reduced in DEE from combustion of RME and JME. This advantage is of particular interest because diesel particulate matter is blamed for causing most of the chronic adverse health effects mentioned above. Nevertheless, PM can be reduced very effectively (more than 99%) by common diesel particle filters (DPF), while NOX remains unaffected and must be treated by additional technologies such as selective catalytic reduction (SCR). Particle number and size distributions were similar between both plant oil methyl esters on one hand and DF and HVO on the other hand. This result probably reflects the similar physicochemical properties of FAME as well as of DF and HVO, respectively. Notably, FAME caused up to 10-fold smaller particle numbers compared to HVO and DF, more or less across the complete size range of measurements with SMPS and ELPI (Figures 3 and 4). Since this trend was also seen for gravimetrically determined PM, it may display a general property of biodiesel emissions.41,42 Thus, hydrogenation of vegetable oils might not be favored concerning particle emissions. Formaldehyde, acetaldehyde, and acrolein were the predominant carbonyls in the emissions of all investigated fuels. JME produced the lowest carbonyl emissions, and a nonsignificant trend showed up toward higher carbonyl emissions of HVO and RME compared to DF. While earlier data for HVO are lacking, the difference between DF and RME was smaller compared to previous studies which reported high amounts of formaldehyde, acetaldehyde, acrolein, and propionaldehyde in biodiesel exhaust exceeding those of DF up to 2.5-fold.42 Up to 2-fold elevated emissions from combustion of pure biodiesel were observed earlier for acetone, crotonaldehyde, valeraldehyde, o-tolualdehyde, and hexanaldehyde compared to DF. However, the standard deviations show a high variability of our and most previous results possibly indicating a problem with sampling or determination of these compounds. In accordance with our present investigation, most recent studies describe a weak mutagenicity and low PAH contents of DEE from contemporary fuels and diesel engines compared to studies from the last Millennium. This effect can be attributed to advanced refinery processes of the fuels (mainly, the elimination of sulfur and aromatics), improved combustion of the engines, and modern systems for post-treatment of the exhausts.42

Figure 7. Emissions of PAHs [ng/ESC test] from combustion of DF, JME, HVO, and RME measured in condensates. PAHs on the righthand side were visualized by multiplying by 10. The amount of the measured PAHs [ng/test] is depicted according to their molecular weight (from left to the right: low to high molecular weight): Nap: naphthalene; Ace: acenaphthylene; Flu: fluorene; Phe: phenanthrene; Ant: anthracene; Fla: fluoranthene; Pyr: pyrene; BaA: benz[a]anthracene; Chr: chrysene; BbFla: benzo[b]fluoranthene; BkFla: benzo[k]fluoranthene; BaPyr: benzo[a]pyrene; DBAnt: dibenz[a,h]anthracene; BPer: benzo[ghi]perylene; IPyr: indeno[1,2,3-cd]pyrene. Results are displayed as means with standard deviations.

Figure 8. Soluble organic fraction (SOF hatched) and solid particulate matter (SPM) in raw exhaust referred to the particle mass which was collected during the whole test cycle [mg/ESC] following combustion of DF, JME, HVO, and RME. Results are displayed as means with standard deviations.

Compared to DF, the combustion of pure HVO reduced most regulated emissions, namely, CO, HC, and NOX in several previous studies, while PM was more or less unaffected.5−7,32,39,40 Our study confirms the results for CO, HC, and NOX but shows a small reduction of PM. RME and JME

Figure 9. Mutations per plate of the PM extracts (left) and condensates (right) in TA98 following combustion of DF, JME, HVO, and RME. Results are displayed as means with standard deviations. 6043



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Figure 10. Mutations per plate of the PM extracts (left) and condensates (right) in TA100 following combustion of DF, JME, HVO, and RME. Results are displayed as means with standard deviations.

These contradictory results may be caused on one hand by the low content of PAHs hardly exceeding the limit of detection. On the other hand, it is well-known that a substantial part of the mutagenicity of DEE is caused by nitroarenes (nitrated PAHs, not analyzed in this study) which mostly show a stronger mutagenicity compared to their parent-PAH.26,27,50 The evaluation of our data is limited, since it is not possible to directly relate the data for PAHs, carbonyls (aldehydes and ketones), and mutagenicity to PM and particle number and size distributions because the latter were measured by use of a partstream dilution tunnel as required by EU-regulations for ESC, while samples for determination of PAHs, carbonyls, and mutagenicity were taken from the undiluted raw exhaust. This was done since, otherwise for PAHs and carbonyls, mutagenicity would have stayed in part below the detection limits. On other hand, the accuracy of the particle measurements requires a dilution of the exhaust. Anyway, the measurement of 16 EPA PAHs and 12 carbonyls covers only a small part of several hundred of these substances in diesel exhaust and such a relation would include strong uncertainties. Estimates concerning PAHs and carbonyls suggest that these compounds contribute to less than 2% to the particle mass of diesel emissions.45

While earlier investigations regularly revealed higher mutagenic effects of the PM extracts of DEE compared to the condensates of the gaseous phase, in this study, we observed a stronger mutagenicity of the condensates. This observation was previously described after combustion of DF in a heavy duty engine complying with the Euro IV standard 36 and for RME in a Euro III engine.43 The effect is probably explained by the smaller amount of emitted particulate matter due to optimized combustion of modern diesel engines and the use of optimized fuels. Due to sufficiently reduced particle amounts in the exhaust available for condensation of PAHs, these substances remain in the gaseous phase leading to an enhanced bacterial mutagenicity of the condensates and less mutagenic effects of the particle extracts.42 Generally, the highest concentrations of PAHs were found in the DF exhaust and the lowest were in HVO emissions. Lower levels of PAHs of HVO were already reported earlier.39,44 RME and JME showed a similar PAH pattern exceeding slightly the values of HVO. However, much higher results were observed for single PAH like benz[a]anthracene and chrysene. Low molecular weight PAHs occurred predominantly in condensates, while the higher molecular weight PAHs were associated more likely with particles. According to their physicochemical properties, high molecular-weight-PAHs show a stronger tendency to condensate and adhere to particles.45 In accordance with this notion, we found PAHs with four and more rings predominantly particle bound and PAHs with three and less rings predominantly in the condensates (Figure 5 and 6). The most pronounced differences concerning the tested fuels were observed for the small PAHs with 3 and less rings in the gaseous phase, especially naphthalene, fluoranthene, phenanthrene,, and anthracene which are generally present in the atmosphere at higher concentrations than the more carcinogenic 4−5 ring PAH. However, these compounds with three and less rings show only weak or no bacterial mutagenicity, while the higher molecular weight PAHs have been shown to cause mutagenic 46 and carcinogenic effects.47,48 The weak mutagenicity of HVO emissions is concordant with the smallest amount of PAHs from combustion of HVO. These results confirm previous studies of Rantanen et al. and Kuronen et al.5,39 Also, the Comet assay was used to study the genotoxicity of emissions from DF, RME, and HVO.49 Dosedependent DNA strand breaks and toxicity of the extracts were observed, but there were no differences between the fuels. However, data of PAH emissions from the other fuels do not fit well to the results of mutagenicity screening. While DF produced the highest amounts of PAHs, the biofuels RME and JME produced the strongest mutagenicity. This was especially pronounced for testing of direct mutagenicity (without S9).

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ASSOCIATED CONTENT

S Supporting Information *

The fuel properties (Table S1) and the results for positive and negative controls of the bacterial reverse mutation test (Table S2) as well as the results concerning HC and CO (Figures S1 and S2). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Advanced Motor Fuels Implementing Agreement (AMF) of the International Energy Agency (IEA).

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REFERENCES

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