Environ. Sci. Technol. 2000, 34, 368-372
Emissions from Two Outboard Engines Operating on Reformulated Gasoline Containing MTBE PETER A. GABELE* U.S. Environmental Protection Agency, Source Apportionment and Characterization Branch, Mail Drop 46, Research Triangle Park, North Carolina 27711 STEVEN M. PYLE U.S. Environmental Protection Agency, Environmental Chemistry Branch, 944 East Harmon Avenue, Mail Drop ECB, Las Vegas, Nevada 89119
Air and water pollutant emissions were measured from two 9.9 HP outboard engines: a two-stroke Evinrude and its four-stroke Honda counterpart. In addition to the measurement of regulated air pollutants, speciated organic pollutants and particulate matter emissions were determined. Aqueous samples were analyzed for MTBE (methyl tertbutyl ether) and BTEX (benzene, toluene, ethylbenzene, and xylene) emission rates. Compared to the four-stroke engine, the two-stroke had dramatically higher levels of toxic organic and particulate matter emissions. The organic material emitted from the two-stroke engine resembles the test gasoline due to the predominance of unburned fuel. Emission rates for PM10 (particulate matter with a diameter of 10 µm or less) are equal to those for PM2.5, implying that emitted particles are all in the respirable range. Aqueous emissions from the two-stroke are also higher: the twostroke’s BTEX and MTBE emissions are, on average, 5 and 24 times higher, respectively, and 3-10% of the MTBE fed to the engine is emitted to the water. Aqueous emission rates, expressed in brake-specific units, tend to increase with decreasing engine load, as do the atmospheric emission rates.
Introduction In 1996 the United States Environmental Protection Agency (U.S. EPA) adopted exhaust emission standards for outboard marine (OB) and personal watercraft (PWC) engines (1). The primary intent of these standards is to reduce hydrocarbon emissions from these sources. The State of California is proposing a stricter set of regulations that are similar to those of the U.S. EPA, except that they accelerate the implementation schedule and considerably reduce the standards’ levels (2). Both regulations, which control emissions of hydrocarbons (HC) and nitrogen oxides (NOx), utilize the same test procedure for certification of emission rates. The certification test procedure involves sampling raw gases in the exhaust manifold before their contact with water. This enables the engine to be tested out-of-the-water which greatly simplifies the process. However, watercraft emissions in the real-world are typically exhausted below the waterline for cooling, silencing, and minimizing exposure to the * Corresponding author phone: (919)541-1397; fax: (919)541-1960; e-mail:
[email protected]. 368 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 3, 2000
exhaust. This means that some of the water soluble and condensed organic materials contained in the exhaust gas and measured using the certification procedure are actually being absorbed into the water during normal operation. Therefore, the test procedure tends to slightly overmeasure the amount being emitted to the atmosphere. In addition to this shortcoming, raw exhaust samples taken from the exhaust manifold do not provide a good sample for organic speciation. Typically, a diluted exhaust sample taken with a constant volume sampling (CVS) system is needed to determine the emission rates of the speciated organic compounds. Knowledge of the organic composition is important because it determines both the photochemical reactivity and the toxicity of the emissions. Published information containing organic speciation from marine engines is not available because widespread use of the certification test procedure precludes their measurement. Even the use of a CVS or other method to dilute nonbubbled raw exhaust would be of limited value because certain pollutants, such as formaldehyde, are readily absorbed in water and would, therefore, be erroneously measured as an air pollutant. Only two studies have been conducted where marine engines’ exhaust gas was bubbled through water prior to sampling with a CVS (3, 4). Both studies, reporting results for routinely measured mobile source exhaust emissions (hydrocarbons, carbon monoxide, nitrogen oxides and carbon dioxide), describe innovative methods that set the stage for a more thorough examination of marine engine emissions. In addition, the studies deliver a limited examination of the resultant water pollution. The BTEX (benzene, toluene, ethylbenzene, and xylene) concentrations are given by Barton for two engines and some alcohol and aldehyde concentrations by Mace for two other engines. Concerns regarding water quality are driving current restrictions pertaining to marine engines in many waterways (2). Specifically, elevated levels of MTBE (methyl tert-butyl ether) in lakes and water supplies have been detected and are due to watercraft combusting gasoline containing MTBE (5). This study employs a large water tank integrated with an engine dynamometer and CVS. The system, which is similar to but larger than that used by Barton, is used to obtain speciated organic and particulate matter emission rates from exhaust gas emerging from the water’s surface. The extent of the gaseous characterization is more detailed than any previous examination of outboard engine emissions. Emissions into the water are also examined in greater detail. Both MTBE and BTEX mass emissions are measured.
Experimental Section Wet Test Emissions Laboratory. The outboard engine mounts on one end of an aluminum tank containing 757 L of water. The tank is fitted with fill, drain, and skim ports that enable the tank to be drained and refilled within a 30 min period. The tank and engine are enclosed in a hood with openings ahead of the engine for intake and dilution air and an exit opening at the rear of the tank for diluted exhaust gas. The engine load is controlled by a 37 kW eddy-current dynamometer located on a bed-plate to the rear of the tank. The dynamometer is connected to the engine by a shaft that penetrates the tank. An engine dynamometer controller is located in a room adjacent to the engine room. Test Procedure. Exhaust gas emissions are generated by operating the outboard engine using prescribed duty cycles. The principal duty cycle used is specified in the current emission certification test for outboard engines (1). It consists 10.1021/es990770e Not subject to U.S. copyright. Publ. 2000 Am. Chem.Soc. Published on Web 12/17/1999
TABLE 1. Test Cycle Descriptions mode number
4
5
Certification Duty Cycle speed (% of rated) 100 80 60 torque (% of rated) 100 71.6 46.5 weighting factor 0.06 0.14 0.15
40 25.3 0.25
idle 0 0.40
Evinrude Two-Stroke 7.26 4.16 2.05
0.77
0
0.75
0
av power (kW) av power (kW) CE4 duty cycle time in mode (s)
1
2
Honda Four-Stroke 7.31 4.20 72
168
3
2.01 180
300
480
of four loaded steady-state modes followed by a steady-state engine idle (see Table 1). Emissions are measured during each of the five steady-state modes with each mode having a duration of 10 min. Weighting factors are applied to the emission rates for the five modes; the weighting factors increase substantially from Mode 1 (full load) to Mode 5 (idle). Most tests in this study used the certification duty cycle, also popularly known as the E4. However, some tests used a composite form of the test devised for this study known as the CE4. The CE4 is a single, non-steady-state test that measures emission rates while the engine is sequenced through each of the five modes of the Certification Duty Cycle. The time spent in each mode is proportional to the weighting factor for that mode. For example, Mode 5 is run for 6.67 times longer than Mode 1 because its weighting factor is 6.67 times greater. Theoretically, the emission rates obtained by running one CE4 test should approximate the weighted emission rate obtained by running the five separate steady-state tests of the certification procedure. Emissions occurring during the short transients between modes probably have a small impact on the overall CE4 emission rates. The extent of equivalency between the CE4 and the certification procedure is being evaluated because its future use as a research tool represents a less expensive option. At least three replicate tests were performed with each engine using the modal tests of the certification test procedure, and no less than four replicates were performed using the CE4 tests. Gaseous and Particulate Emissions Measurement. Exhaust emission rates were determined for carbon monoxide (CO) and NOx using standard sampling, analytical, and calculation procedures required for measuring emissions from small engines (6). The CO concentrations in bag and real-time samples were measured using a nondispersive infrared analyzer, and NOx concentrations were measured using a chemiluminescent analyzer. The non-methane organic gas (NMOG) emissions were determined by taking the sum of the individual non-methane HC emissions following analysis with a gas chromatography-flame ionization detector (GC/FID) and then adding in the oxygenate (alcohol, ether, aldehyde, and ketone) emissions. Dilute exhaust samples were collected in 60-L Tedlar bags for hydrocarbon and oxygenate speciation. The GC speciation methods are essentially the same as those used in the Auto/ Oil Air Quality Improvement Research Program (7). A background sample was taken during the test. Aldehydes were sampled through a heated sample line (110 °C) and collected on dinitrophenylhydrazine (DNPH)coated silica gel cartridges. Two cartridges were drawn during each test: one from the diluted exhaust gas and one from the background. The aldehyde samples, trapped on the cartridge as individual DNPH aldehyde derivatives, were then analyzed by high-performance liquid chromatography (7). Particulate matter was isokinetically sampled using two straight stainless steel probes that extend from the rear of an 20.3 cm diameter, 3 m long dilution tube. One of the sample
probes was connected to a PM10 and the other to a PM2.5 cyclone (University Research Glassware, Carrboro, NC). Particles exiting the cyclones were collected onto 47 mm diameter, 2.0 µm pore size Gelman Zefluor filters that were equilibrated for 24 h before being weighed. Emissions’ Reactivity. Ozone-forming potential of the exhaust volatile organic compounds (VOC) is based upon the incremental reactivity approach developed by Carter and Atkinson (8). Application of this concept has led to the development of the Maximum Incremental Reactivity (MIR) method that expresses the reactivity of exhaust NMOG and CO from the test engine (9). The method assigns a specific reactivity level to each of the organic species and to CO and calculates a reactivity-weighted emission (RWE) rate for each species by multiplying the species’ specific reactivity times its emission rate. The RWE rate for an exhaust sample is obtained by summing all of the individual RWE rates for each species present. The RWE rate, expressed in units of grams of ozone per kilowatt-hour, is a useful measure of the ozone potential of the CO and organic emissions in urban atmospheres, where the VOC-to-NOx ratios are relatively low (approximately 6). Aqueous Sampling and Analysis. Water samples were collected at the start and end of the emissions test. Both samples were drawn from approximately the center of the tank using a quarter inch stainless steel sample tube. The samples were collected in 1.8 mL vials, stored at 4 °C, and then shipped to the National Exposure Research Laboratory in Las Vegas, NV for analysis. Quantitation of aqueous samples was carried out on a Finnigan (Sunnyvale, CA) Model GCQ ion trap mass spectrometer using Version 2.2 software. The separation column was a Restek, Inc. (Bellefonte, PA) 30 m × 0.32 mm XTI-5 fused-silica capillary column coated with a 0.5 µm film of bonded 95% dimethyl-5% phenyl polysiloxane liquid phase. The end of the analytical column was inserted directly into the vacuum manifold and the linear velocity maintained at 45 cm/s. An initial 0.2 min surge pressure of 30 psi was used to facilitate removal of residual water. These capillary column conditions maintained helium flow into the manifold at the manufacturer recommended 1.5 mL/min. The ion trap detector was scanned from 50 to 300 amu at 0.6 scan/s (each scan was an average of 5 µscans) with the manifold temperature at 225 EC, a 60-s solvent delay, and a 0 mmu/ 100 amu mass defect. For groups of samples with concentrations less than 1 ppm, the ion trap was run in the selected ion monitoring (SIM) mode. The gas chromatograph was a Varian (Walnut Creek, CA) Model 3400 equipped with a split/ splitless injector and a CTC Model A200S autosampler. After a 1 min hold, the GC was temperature programmed from 40 to 208 EC at 12 deg/min for total run time 15 min. The transfer line was held at 275 EC, and the split/splitless injector was run in the split mode at 250 EC. A Pentium personal computer controlled the autosampler, GC, and mass spectrometer (MS) acquisition. Aqueous calibration standards were prepared in 1.8 mL autosampler vials using commercially available methanolic standards. The vial was filled with distilled water, and the appropriate volume was added through the vial septum using a measuring syringe. Calibration was accomplished at the 2, 5, 10, and 20 ppm level in triplicate. Check standards at the 10 ppm level were used to periodically verify that the instrument was in calibration. Test Engines and Fuel. Outboard engines come in two types of designs: two-stroke and four-stroke internal combustion engines. The two-stroke variety is much more prevalent compared to its four-stroke counterpart but has hydrocarbon emissions that are 10-20 times higher (10). Many of the larger, new technology two-stroke engines are now equipped with fuel injection, which reduces emission VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Engine Descriptions manufacturer model number engine cycle engine weight (kg) engine displacement (cc) rated power (kW) rated speed (rpm) gear ratio number of cylinders fuel system fuel consumption @ mode 1 fuel/oil ratio
Evinrude E10SELECC two-stroke 27.6 255 7.4 5000 2.42 2 carburetor 5.87 L/h 50:1
Honda BF9.9A four-stroke 47.2 240 7.4 5000 2.12 2 carburetor 6.62 L/h N/A
RFG 0.7394 0.0045 1.19 27.0 5.1 55.1 12.6 96.6 87.3
carbon, wt % hydrogen, wt % Reid vapor pressure, psi distillation, °C IBP 10% 50% 90% EP
13.8 86.2 6.65 40 58 94 150 193
rates considerably, but hydrocarbon emissions are still typically much higher compared to those from a four-stroke engine. Emissions from two outboard engines, a two-stroke Evinrude and a four-stroke Honda, were examined in this study. Both engines were “nonregulated” because their model years, 1997 and 1995, were before the standard took effect in 1998. The engines were carburetor equipped and rated at 7.4 kW (9.9 hp). The two-stroke engine was purchased new and was broken-in with over 20 h of operation prior to testing. The four-stroke engine was obtained from Environment Canada (EC) where it had undergone testing in a separate study (3). It had been operated for about 50 h prior to testing in this study. Both engines were tested by both EPA and EC in order to examine emissions’ reproducibility. A description of the test engines is given in Table 2. The test fuel represents a typical reformulated gasoline that must contain 2.0% oxygen by weight. This corresponds to approximately 11 vol % of MTBE, the most frequently used additive nationwide to oxygenate gasoline. The test fuel, which contains 12.6 vol % of MTBE, was purchased from Phillips Petroleum and was taken from a lot marketed for sale in California. A more complete description of the fuel is given in Table 3.
Results and Discussion General Observations. Most of the emissions data are given in units of grams per kilowatt-hour. Multiplying these values by the average engine power for the test that was run (see Table 1) results in a gram per hour emission rate that better reflects the mass being emitted during the test. For example, the two-stroke engine had CO emission rates of 345 g/kW-h and 903 g/kW-h for Mode 1 (full rated load) and Mode 4 (approximately 10% of rated load), respectively. This corresponds to emission rates of 2507 g/h for Mode 1 and 695 g/h for Mode 4. Also given in Table 1 are the modal weighting factors used in calculating the emission rate for the certification test. Note that the idle mode is weighted 40%, while the full-rated load mode is weighted only 6%. For this reason, focusing efforts to achieve lower idle emissions would seem an effective strategy to attain lower certification emission rates. Ideally, the weighting factors reflect the extent to which an engine resides at the different loads in the real world. 370
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react. PM (mg/kW-h) wt’ed HC NMOG CO NOx 10 µm/2.5 µm emiss
Evinrude Two-Stroke Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 idle (g/h) weighted (g/kW-h) CE4 results (g/kW-h) Environment Canada results
133 182 294 607 406 322 356 343
137 163 310 643 368 343 348 x
345 581 709 903 283 655 672 617
1.3 0.5 0.8 1.6 0.8 1.2 2.2 1.3
3.0/2.7 5.5/5.5 8.1/8.5 17.9/17.9 4.7/4.7 8.1/8.1 5.3/5.4 x
439 581 1005 2061 1116 1046 1096 x
Honda Four-Stroke
TABLE 3. Fuel Description fuel type specific gravity sulfur, wt % benzene, ppmC% aromatics, vol % olefins, vol % paraffin, vol % MTBE, vol % research octane no. motor octane no.
TABLE 4. Atmospheric Ozone Precursor and Particulate Matter Emission Rates (g/kW-h)
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Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 idle (g/h) weighted (g/kW-h) CE4 results Environment Canada set no. 1 (initial tests) Environment Canada set no. 2 (final tests)
11 11 14 24 11 16 16 19
11 10 13 24 13 16 16 x
244 5.3 99 10.7 155 6.8 242 3.7 78 1.2 190 7.8 217 7.3 300 6.1
0.02/0.02 0.01/0.02 0.02/0.02 0.08/0.06 0.04/0.03 0.04/0.03 0.03/0.02 x
52 44 59 108 59 73 75 x
32
x
368
x
x
3.4
There was good agreement between Evinrude emission rates obtained at EPA and EC. These tests were all run within 6 months of each other. Emission rates from the Honda were more varied. Prior to its testing at EPA, the Honda had been previously tested for regulated emissions on two separate occasions at EC. Emission rates varied significantly in those separate test sets (see last entries in Table 4) that were 7 months apart. During that 7 month period, the engine was removed and then later reinstalled on the “test bench”. The increase in emission rates of HC and CO for the second set of tests suggests that something was causing the engine to operate at richer fuel-air mixtures. This also suggests that emissions from outboard engines are extremely sensitive to operating parameters that can vary significantly over the life of the engine. Following its delivery to EPA about 18 months later, the Honda’s carburetor required cleaning before the engine would operate properly. Results obtained by EPA show slightly lower HCs (-16%) and CO (-33%) emissions and higher NOx (+16%) emissions compared to the initial test set at EC. These data imply that following the carburetor work at EPA, the Honda was operating at air-fuel ratios close to those of the initial study at EC when the engine was new. There was reasonably good agreement between atmospheric emission rates from the two duty cycles (certification versus CE4). Future use of the CE4 cycle is encouraged in research settings where extensive analyses are needed, because five tests can be compacted into one. Atmospheric Emission Rates. The results for regulated emissions (HC, CO, and NOx) given in Table 4 resemble those from other studies that have compared regulated emissions from two- and four-stroke engines (1-3). As mentioned previously, these engines were not required to comply with any emission standard; however, it is pertinent to note that the four-stroke engine easily complies with the 1998 standard of 225 g/kW-h for combined HC and NOx emissions. Compared to the two-stroke engine, the Honda’s hydrocarbon and carbon monoxide emission rates are dramatically lower, while nitrogen oxide emissions are higher. Extremely high hydrocarbon emission with two-stroke engines is the reason that regulations are forcing their replacement or refinement as economics permit. In addition to the increased ozone potential associated with high hydrocarbon emissions, toxic emissions are proportionately higher as well. This effect
TABLE 5. Atmospheric Toxic Emission Rates (g/kW-h) 1,3-butadiene Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 idle (g/h) weighted (g/kW-h) CE4 results Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 idle (g/h) weighted (g/kW-h) CE4 results
benzene
formaldehyde
acetaldehyde
aggregate
Evinrude Two-Stroke Engine 0.12 1.61 0.11 0.15 1.92 0.14 0.37 3.82 0.30 0.80 8.01 0.68 0.20 4.93 0.28
0.03 0.04 0.06 0.14 0.06
1.87 2.25 4.56 9.64 5.48
0.45
3.99
0.28
0.07
4.79
0.33
4.28
0.43
0.12
5.16
Honda Four-Stroke 0.05 0.25 0.02 0.06 0.23 0.03 0.09 0.31 0.04 0.16 0.67 0.06 0.05 0.42 0.03
0.004 0.009 0.008 0.01 0.007
0.33 0.34 0.45 0.91 0.60
0.14
0.53
0.06
0.01
0.74
0.10
0.42
0.04
0.01
0.58
can be seen by comparing the toxic emissions (1,3-butadiene, benzene, formaldehyde, and acetaldehyde) for the two engine types (see Table 5). The aggregate toxic emissions are about a factor of 10 lower and the ozone potential about a factor of 15 lower with the four-stroke engine. Particulate matter emission rates are also greatly affected by engine choice. Both the PM2.5 and PM10 emission rates are given in Table 4. Practically all of the emitted particles are less than 2.5 microns since the emission rates for the two particle sizes are nearly equal for every test. The repeatability as measured using relative standard deviations was good with the two-stroke engine but suffered some with the fourstroke engine because of small changes in small emission rates. Emission rates with the two-stroke engine were on average about 300 times higher than those from its fourstroke counterpart. It is suspected that the difference would be even more pronounced had the engines been tested out of the water. The water, through which the exhaust is bubbled, probably captures a disproportionately larger share of the unburned oil particles in the two-stroke’s exhaust. Organic Composition. The two-stroke engine inducts a mixture of gasoline and oil during the intake stroke and expels the gases during the exhaust stroke. Composition of these exhaust hydrocarbons consists largely of unburned fuel. Figure 1 shows the carbon number distribution for the test gasoline compared to those distributions for the organic emissions from the Evinrude (two-stroke) and Honda (fourstroke) engine. The similarity between distributions for the Evinrude exhaust and the fuel illustrates the predominance of unburned fuel in the two-stroke exhaust gas. Exhaust organic compounds from the two-stroke engine, like the test fuel used, consist of about 50% paraffin and 30% aromatic hydrocarbons. The four-stroke’s exhaust contains significantly larger olefin and smaller paraffin fractions. The principal olefin compounds emitted from the four-stroke engine, namely, ethylene, propylene, and isobutylene, are produced during combustion, and their fractions are much lower in two-stroke emissions. Ozone Potential. The 10 compounds in the test fuel having the greatest impact on ozone formation (a function of their MIR reactivity and quantity) are ranked in Table 6. The extent of their contribution to the RWE (reactivity weighted emissions) from both engines is also given as a ranking. The M&P xylene compounds would contribute the most to the RWE if one gram of fuel were evaporated, and they contribute the
FIGURE 1. Carbon number distribution for hydrocarbons in fuel and engine exhaust gases.
TABLE 6. Top Ten Ozone Producing Compounds in Test Fuel and Their Ranking in the Exhaust Organic Emissions top 10 compounds in fuel
rank in Evinrude exhaust
rank in Honda exhaust
M&P xylene 1,2,4-trimethlybenzene toluene o-xylene 1-methyl-3-ethylbenzene 1,3,5-trimethylbenzene MTBE isopentane isooctane 2,3-dimethylpentane
1 3 2 4 5 8 15 7 10 11
3 5 4 7 8 9 18 15 13 14
most and the third most in the organic emissions from the Evinrude and Honda engines, respectively. Eight of the 10 biggest ozone contributing compounds (not counting CO) from the two-stroke emissions are also included in the 10 fuel compounds having the greatest impact on ozone formation. Correspondingly, the four-stroke engine exhaust has six such compounds in common with the fuel’s top ten. Thus, the strong influence of fuel on ozone potential is clear. But it should be noted that for the four-stroke engine, three olefins (ethylene, propylene, and isobutylene) contribute 18% of total RWE. As mentioned earlier, these compounds are not present in the fuel but are produced during combustion. Carbon monoxide also contributes another 36% to the fourstroke’s ozone potential but only 3% to the two-stroke’s. Aqueous Emissions. The MTBE and BTEX emission rates to the water are given in Table 7 for both engines. A breakdown of the certification test results given in Table 7 shows emission rates for each of the five modes. The results look reasonable in that they show the familiar trend seen in the atmospheric data of increasing emission rates with decrease in engine load. An attempt was made to measure aqueous emissions during the CE4 test; however, the data appeared erratic. It is suspected that the test does not allow enough time in the highly loaded modes (the engine idles for 8 min while it runs at rated load for only 72 s) to obtain a good water sample. The result is a very clean water sample VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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air for the four-stroke engine are less than 1 and 2%, respectively, for all of the modes.
TABLE 7. Aqueous Emission Rates (g/kW-h) MTBE benzene toluene ethylbenzene xylenes Evinrude Two-Stroke Mode 1 3.34 0.11 0.35 Mode 2 3.26 0.14 0.38 Mode 3 4.93 0.22 0.50 Mode 4 7.91 0.19 0.70 Mode 5 idle (g/h) 10.27 0.20 0.99 wt’ed 6.91 0.21 0.70 CE4 results 11.81 0.79 2.69 Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 idle (g/h) wt’ed CE4 results
Honda Four-Stroke 0.19 0 0.08 0.19 0.14 0.11 0.23 0.16 0.12 0.30 0 0.10 0.29 0 0.07 0.29 0.07 0.12 0.13 0 0.10
0.12 0.11 0.17 0.19 0.26 0.20 0.95
0.27 0.28 0.36 0.51 0.86 0.55 3.48
0.03 0.03 0.04 0.03 0.02 0.03 0.02
0.07 0.07 0.09 0.07 0.06 0.09 0.09
Acknowledgments We thank the members of our research team who conducted the tests and analyzed samples. Special thanks go to Jerry Faircloth, Versal Mason, and Mike Kirby for their hard work in the engine laboratory. Colleen Loomis, Christy Pack, and Angela Farinacci are also acknowledged for their diligent work with the gas and liquid chromatographic equipment. Finally, I would like to thank Peter Barton and his colleagues at Environment Canada for the use of their engine, and for making our cooperative effort a very pleasant experience. The information in this paper has been funded by the Environmental Protection Agency. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
Literature Cited that makes the analysis difficult. In contrast, during the certification test, each mode is tested for 10 min which enables enough time to obtain good water samples for all five modes of the test. As expected, emissions from the two-stroke engine are much higher than those from the four-stroke counterpart. Barton et al. (3) measured the two- to four-stroke ratio of aggregate BTEX emissions at about 12. The ratios in this study vary between 3 and 15 depending upon the mode examined. The ratio for the idle mode is 15, but lower values occur for Modes 1-4 where the engine was operated at higher loads. The same ratios for MTBE emissions are higher, varying between 17 and 35 depending upon the mode examined. Again, the ratios tend to be lower for high power modes. Results from a real world study conducted at Lake Tahoe and Donner Lake concluded that carbureted two-stroke engines released 10-15 times more gasoline than the fourstoke engines (11). These results, though highly qualitative, are in rough agreement with the MTBE ratios (two-stroke to four-stroke) obtained here with the engines operating under loaded conditions. Of course, this assumes that the MTBE levels in the water are a good indicator of the levels of unburned gasoline being discharged. Of the MTBE consumed by the engine, 3-10% goes into the water and 20-40% to the air for the two-stroke engine tested. These distributions are considerably more focused when the idle mode is eliminated: 3-5% to the water and 18-21% to the air. The percentages going to the water and
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(1) Federal Register, Vol. 61, No. 26, February 7, 1996. (2) State of California, Air Resources Board, Staff Report. Public hearing to consider adoption of emission standards and test procedures for new 2001 and later model year spark-ignition marine engines; October 23, 1998. (3) Barton, P. J.; Fearn, J. SAE Paper 972740. (4) Mace, B. E.; Nine, R. D.; Clark, N. N.; Vanyo, T. J.; Remcho, V. T.; Morrison, R. W.; McLaughlin, L. W. SAE Paper 980681. (5) Reuter, J. E.; Allen, B. C.; Richards, R. C.; Pankow, J. F.; Goldman, C. R.; Scholl, R. L.; Seyfried, J. S. Environ. Sci. Technol. 1998, 32, 3666. (6) Federal Register, 40 CFR, Parts 9 and 90, Final Rule, 60(127), July 3, 1995. (7) Siegl, W. O.; Richert, W. F. O.; Jensen, T. E.; Scheutzle, D.; Swarin, S. J.; Loo, J. F.; Prostak, A.; Nagy, D.; Schlenker, A. M. SAE Paper 930142. (8) Carter, W. P. L.; Atkinson, R. J.; Environ. Sci. Technol. 1987, 21, 864. (9) Lowi, A. Jr.; Carter, W. P. L. SAE Paper 900710. (10) Nonroad Engine and Vehicle Emission Study - Report; EPA21A-2001; U.S. Environmental Protection Agency, Certification Division, Office of Mobile Sources, Office of Air and Radiation: Washington, DC, November 1991. (11) Allen, B. C.; Reuter, J. E.; Goldman, C. R.; Fiore, M. F.; Miller, G. C. Lake Tahoe Motorized Watercraft Report - An Integration of Water Quality, Watercraft Use and Ecotoxicology Issues; John Muir Institute for the Government, Tahoe Research Group, Preliminary Draft Report, Davis, CA, 1998.
Received for review July 7, 1999. Revised manuscript received October 11, 1999. Accepted November 8, 1999. ES990770E
