United States Air and Radiation EPA420-R-98-009 Environmental Protection August 1998 Agency &EPA Emissions of Nitrous Oxide from Highway Mobile Sources Comments on the Draft Inventory of U. S. Greenhouse Gas Emissions and Sinks, 1990-1996 (March 1998) > Printed on Recycled Paper ------- EPA420-R-98-009 August 1998 of Comments on the Draff inventory of U.S. Emissions and Sinks, Harvey Michaels Assessment and Modeling Division Office of Mobile Sources U.S. Environmental Protection Agency NOTICE This technical report does not necessarily represent final EPA decisions or positions. It is intended to present technical analysis of issues using data which are currently available. The purpose in the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments which may form the basis for a final EPA decision, position, or regulatory action. ------- TABLE OF CONTENTS 1 INTRODUCTION Page 1 2 AN ANALYSIS OF THE DATA SOURCES AND METHODS USED TO OBTAIN THE EMISSION FACTORS FOR NITROUS OXIDE FROM GASOLINE HIGHWAY VEHICLES IN THE RECENT DRAFT INVENTORY Page 3 3 IMPROVED ESTIMATES OF EMISSION FACTORS FOR GASOLINE HIGHWAY VEHICLES Page 5 4 OTHER ISSUES Page 11 5 EFFORTS THAT WOULD IMPROVE FUTURE INVENTORIES Page 14 6 CONSOLIDATED LIST OF SPECIFIC CHANGES TO THE DRAFT INVENTORY Page 16 7 REFERENCES Page 19 APPENDIX A A DETAILED DISCUSSION OF THE ORIGIN OF THE EMISSION FACTORS FOR NITROUS OXIDE FOR GASOLINE HIGHWAY VEHICLES IN THE DRAFT INVENTORY Page A-l APPENDIX B NVFEL TESTING PROGRAM Page B-l APPENDIX C ASSUMED FUEL ECONOMIES WHOSE RATIOS WERE USED TO GENERATE EMISSION FACTORS FOR VEHICLES FOR WHICH THERE WERE NO DATA Page C-l Page ii ------- EMISSIONS OF NITROUS OXIDE FROM MOBILE SOURCES: COMMENTS ON THE DRAFT INVENTORY OF U.S. GREENHOUSE GAS EMISSIONS AND SINKS, 1990-1996 (MARCH 1998) August 13, 1998 1 INTRODUCTION The estimate of the contribution of nitrous oxide from mobile sources to total U.S. emissions of greenhouse gases went from one-half percent in the last official inventory, published in 1997 (U.S. EPA) to three percent in the March 10, 1998, draft Inventory of U.S. Greehouse Gas Emissions and Sinks 1990-1996 (U.S. EPA), which will be referred to in these comments as the Draft Inventory. The primary reason for this change is the use of much larger emission factors for gasoline highway vehicles, rather than increases in vehicle miles traveled. OMS believes that these emission factors are considerably larger than they should be. Therefore, these comments will focus primarily on the origin and validity of the emission factors used in the Draft Inventory and on the development of better ones. The emission factors for passenger vehicles from the last official Inventory, from the 3/10/98 Draft Inventory, and from OMS's proposed revisions that are developed in this document, are listed in the following table. Control Technology LEV Advanced 3 Way (Tier 1) Early 3-way (Tier 0) Oxidation Catalyst Non-Catalyst Uncontrolled N2O Emission Factors for Passenger Vehicles Last Official Inventory (g/km) 0.019 0.046 0.027 0.005 0.005 3/1 0/98 Draft Inventory (g/km) 0.040 0.170 0.170 0.075 0.020 0.020 OMS Revision (g/km) 0.018 0.029 0.051 0.032 0.010 0.010 The Draft Inventory adopted the emission factors for U. S. vehicles from the Revised 1996IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 1997), which are referred to in these comments as the IPCC Guidelines. They list emission factors for European cars that are between four and thirty-four times lower than for similar U.S. vehicles: Page 1 ------- Comparison of estimated emission factors in the IPCC Guidelines between U.S. and European passenger vehicles Control Technology LEV Advanced 3 Way Early 3-way Oxidation Catalyst Non-Catalyst Uncontrolled Emission Factors (g/mi) U.S. Passenger Vehicles 0.064 0.274 0.274 0.121 0.032 0.032 European Passenger Vehicles 0.08 0.008 0.008 0.008 0.008 1.1 Control technology terminology For U.S. vehicles, the following control technology designations are more appropriate than those used in the Draft Inventory: For "Early three-way catalyst," substitute "Tier 0." For "Three-way catalyst" or "Advanced 3 Way," substitute "Tier 1." Tier 0, Tier 1 and LEV (Low Emission Vehicle) are not control technologies per se, but emissions regulations. They do, however, correspond to combinations of control technology and engine design. Tier 0 refers to standards earlier than Tier 1 that applied to vehicles equipped with three-way catalysts (TWCs). Tier Is and LEVs both have TWCs, but the data show that their more stringent NOX standards are associated with lower nitrous oxide emissions as well. The introduction dates for "early three-way catalysts" and "advanced three-way catalysts" in the Draft Inventory correspond approximately to the introduction of Tier 0 and Tier 1 emissions regulations (see Table C-7 in the Draft Inventory or Section 4.2 below). The assignments of control technologies to model years are revised in Section 4.2. 1.2 Purposes and overview The purposes of these comments are 1) to review the data supporting the nitrous oxide emission factors used in the Draft Inventory, 2) to provide revised emission factors, 3) to recommend changes in other factors affecting nitrous oxide emissions, and 4) to recommend changes in future inventories. Section 2 reviews the data sources and methods supporting the nitrous oxide emission factors used in the Draft Inventory. Section 3 presents the development of revised emission factors. This development is based on a review of the literature (Section 3.1) and on recent tests conducted at EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) (Section 3.2). Section 4 discusses other issues that affect the calculation of U.S. emissions of nitrous oxide from mobile sources. These include diesel emission factors (Section 4.1), assignment of control Page 2 ------- technology by model year (Section 4.2), distribution of model years in each calendar year (Section 4.3), and uncertainty (Section 4.4). Section 5 discusses further work to better evaluate the contribution of mobile sources to U.S. emissions of nitrous oxide. Section 6 is a consolidated list of the specific changes recommended for the Draft Inventory. 2 AN ANALYSIS OF THE DATA SOURCES AND METHODS USED TO OBTAIN THE EMISSION FACTORS FOR NITROUS OXIDE FROM GASOLINE HIGHWAY VEHICLES IN THE RECENT DRAFT INVENTORY The trail of references from the Draft Inventory back to the original data sources is described briefly below. A more detailed analysis is provided in Appendix A. The grams/mile emission factors for U.S. mobile sources used in the Draft Inventory were taken from the IPCC Guidelines. The grams/mile emission factors for U.S. vehicles in the IPCC Guidelines come from a report prepared by Weaver and Chan (1996): "Mobile source emission factors for global warming gases." Weaver and Chan (1996) obtained their grams/mile emission factors from the last column of Table 7 in Ballantyne et al. (1994). The heading of this column is "Current Canadian Estimates: EPS Inventory." The reference for the last column of Table 7 in Ballantyne et al. is to Jaques (1992), Canada's Greenhouse Gas Emissions: Estimates for 1990, published by the Canadian Government. Ballantyne et al. obtained the grams/mile emission factors (for aged TWCs, new TWCs, and oxidation catalysts) in this column from the grams/kilogram emission factors presented in Jaques, by assuming fuel economies of 9.4, 11.9, and 6 km/L respectively and a standard value for the density of gasoline. The fuel economies are from Jaques's Table 16 and the gasoline density from Table 32. It is not clear where Ballantyne et al. obtained their grams/mile emission factor for non-catalyst vehicles, since it is roughly half the value that would be derived from Jaques by the method described. Jaques's emission factors for vehicles without catalysts, vehicles equipped with aged TWCs and vehicles equipped with new TWCs, are the averages of the first two lines of de Soete's (1989) Table XXIX. Jaques converts these averages, which are in units of g/km, to units of g/kg by assuming a uniform fuel economy of 8.5 km/L and a gasoline density of 0.75 kg/L. Jaques's emission factor for oxidation catalyst vehicles is the same as that for new TWC vehicles. Since none of his references support this emission factor for oxidation catalysts, it is possible that he simply adopted the emission factor for new TWCs. The average emission factor for oxidation catalysts from de Soete's Table XIV was 70% higher than the one Jaques uses. Page 3 ------- Lines 1 and 2 of De Soete's Table XXIX are averages of emission factors in his Table XIV. Line 1 is the average of Table XIV lines 2, 4-7, and 11-19, and represents the data from three studies which measured emission factors on a total of five cars tested without catalysts, with new TWCs, and with aged TWCs on various European dynamometer test cycles. Line 2 is the average of Table XIV lines 11-19, and represents the data from a single car tested without a catalyst, with eight new TWCs and with the same eight TWCs bench aged. Therefore, Jaques's average of lines 1 and 2 of de Soete's Table XXIX double weights lines 11-19 from Table XIV. Since the averages are of individual data points, and approximately 80% of the new and aged TWC data come from lines 11-19, Jaques's emission factors for TWCs are derived approximately 90% from a single study involving one car and eight non-production catalysts. De Soete's Table XIV lines 11-19 refer to one study, Prigent et al. (1991), in which one car was tested without a catalyst, with eight different non-production catalysts, and then with the same eight catalysts bench-aged. The catalysts were located 1.4 m from the engine. Table XIV line 2 refers to Lindskog (1988), in which one non-catalyst car and one car equipped with a TWC were tested on the Swedish driving cycle. Table XIV lines 4-7 refer to Prigent et al. (1989), in which two cars were each tested with and without new TWCs. In summary: All the emission factors originate from testing done on five cars using European test cycles. Fuel sulfur content for these tests was unspecified. The new and aged TWC emission factors are based 90% on a single study using a single car with eight non-production catalysts, new and bench-aged, with the catalysts located 1.4 m from the engine. The other 10% of the data for the TWC emission factors came from two studies and three more cars, all tested on European driving cycles only. The non-catalyst emission factors were derived from four cars. The emission factor for oxidation catalyst vehicles does not appear to be based on testing, but is instead the same emission factor used for new TWCs. 3 IMPROVED ESTIMATES OF EMISSION FACTORS FOR GASOLINE HIGHWAY VEHICLES Compared to regulated tailpipe emissions, there exist relatively few data that can be used to Page 4 ------- estimate nitrous oxide emission factors for gasoline highway vehicles. Nitrous oxide is not a criteria pollutant, and measurements of it in automobile exhaust are not routinely collected. Many of the recent measurements have been part of research efforts attempting to understand why and under what conditions TWCs produce nitrous oxide, rather than trying to characterize the U.S. fleet. OMS determined emission factors for Tier 0 and earlier vehicles primarily from the published literature (Section 3.1). For Tier 1 vehicles and for LEVs, data was used from the recent testing program at NVFEL (Section 3.2). Section 3.3 discusses the limited data that we have for trucks. Section 3.4 summarizes our recommendations for emission factors by vehicle type and control technology. 3.1 Emission factors for Tier 0 and earlier passenger cars In looking for a better estimate of emission factors, OMS has decided to review only published values for the composite of the standard FTP driving cycle, since it is the standard driving cycle for the U.S. To do otherwise would require reconciling alternative test cycles, tunnel studies, and remote sensing studies—an effort beyond the scope of this review. To determine emission factors for Tier 0 and earlier vehicles, the following published studies were included in the analysis: Prigent and de Soete (1989) Dasch(1992) Smith and Carey (1982) Smith and Black (1980) Urban and Garbe (1979) Urban and Garbe (1980) Ballantyne et al. (1994) Barton and Simpson (1994) Braddock(1981) Also included were two measurements of one Tier 0 vehicle that the NVFEL included in its recent study of nitrous oxide emissions from Tier 1 vehicles and LEVs. Light trucks are analyzed separately, since their emissions are significantly higher than passenger vehicles. The above studies that included light trucks also treated them separately from passenger vehicles. Emission factors for trucks are addressed in Section 3.3 below. Some authors distinguish "dual bed" catalysts from TWCs, but the distinction is not clear, and we have followed most authors in considering dual-bed catalysts as a form of TWC. There is evidence that aged TWCs emit more nitrous oxide than new ones. For this reason, we have separated the data into "new" and "aged" (or "old"). "New" means a vehicle that was Page 5 ------- supplied by a manufacturer for testing and has less than a few thousand miles on the odometer. Everything else is aged or old. The results are summarized in the following table: Catalyst age All ages New Aged Parameter mg/mi n std. err. of mean mg/mi n std. err. of mean mg/mi n std. err. of mean Catalyst Type All 56. 50 6.5 42.7 29 4.8 74.2 21 13.2 None 17. 3. 13. 17. 3. 13. Oxidation 51.7 11 19.1 37.8 4 12. 59.7 7 29.7 3-Way 60.5 36 6.8 47.2 22 5.4 81.5 14 13.8 The study by Ballantyne et al. has been excluded from our averaging, because the fuel they used contained 700 ppm sulfur, roughly double what might be expected in U.S. gasoline. The sulfur content of the fuel used in Braddock (1981) was 250 ppm. It was 290 ppm in Urban and Garbe (1979 and 1980), Smith and Carey (1982), and Smith and Black (1980). It was 500 ppm in Barton and Simpson. Sulfur in fuel has been shown to degrade catalyst performance with respect to conventional emissions (see, e.g., Lindhjem 1995 and Monroe et al. 1991). Newly acquired data at NVFEL, discussed below, indicates that emissions of nitrous oxide were significantly higher using Clean Air Act Baseline (CAAB) fuel, a fuel intended to represent a "normal" commercial fuel and which contained 285 ppm sulfur, than when using Indolene, a fuel used in vehicle certification and which contained 24 ppm sulfur. We believe that the higher nitrous oxide emissions were due to the higher sulfur content of CAAB fuel. The fuel analyses and our reasons for believing that the differences in nitrous oxide emissions were due to differences in sulfur content rather than to differences in other fuel parameters are detailed in Appendix B. For comparison, the following table presents emission factors for new and aged TWCs for all data, for data excluding Ballantyne et al. (1994), and for Ballantyne et al. alone. Units are mg/mi, with the number of data points in parentheses. All Without Ballantyne et al. Ballantyne et al. only New TWC 50.4 (25) 47.2 (22) 74. (3) Aged TWC 97.7 (22) 81.5(14) 126. (8) Page 6 ------- Including Ballantyne would increase the aged TWC emission factor from 0.08 to 0.1 g/mi. 3.2 Emission factors for Tier 1 and LEV vehicles: recent measurements by the NVFEL A measurement program was undertaken during June and July, 1998, to determine nitrous oxide emissions from aged Tier 1 and LEV vehicles using commercial fuels. 23 vehicles were tested: 18 Tier 1 vehicles, 4 LEVs, and one Tier 0 vehicle that was recruited in error. One of the Tier Is was recruited specifically to verify the results for a single high-emitting pickup truck. Tier 1 odometers ranged from 16,000 to 75,000 miles. All four LEVs were obtained from their manufacturers. Three of the four were equipped with TWCs that had been bench-aged to 100,000 miles. Three of the odometers read about 5,000 miles; the fourth read about 169,000 miles. Vehicles were tested with air conditioning (A/C) off at 75°F and on at 95 °F. All vehicles except one LEV and one Tier 1 were tested using CAAB fuel, a commercial fuel containing 285 ppm sulfur. All of the LEVs and three of the Tier 1 vehicles were tested with Indolene, a low- sulfur fuel used in vehicle certification. The testing schedule and fuel analyses are in Appendix B. The schedule included 23 vehicles and 50 samples. In order to estimate the emission factors for Tier 1 vehicles, we averaged only tests run with CAAB fuel, and we omitted the second high-emitting pickup truck that was recruited specifically to verify the first one. The following table shows these results: Tier 1 emission factors from NVFEL program Vehicles included in average All Passenger vehicles Light trucks and SUVs Emission factor (mg/mi) 63.6 46.3 108.9 Number of vehicles 17 12 5 Number of samples 29 21 8 Std. err. mean (mg/mi) 7.1 5.0 11.8 Range (mg/mi) 24-167 24-124 80-167 The emission factor of 46 mg/mi for these Tier 1 passenger vehicles compares favorably with the emission factor of 82 mg/mi for Tier 0 vehicles equipped with TWCs. The following summarizes the LEV emission factors under our test program. All the LEVs were obtained from their manufacturers. Three had catalysts bench-aged to 100,000 miles. Page 7 ------- LEV emission factors from NVFEL program Fuel CAAB Fuel Indolene Emission factor (mg/mi) 77.8 28.3 Number of vehicles 3 4 Number of samples 6 8 Std. err. mean (mg/mi) 14.7 2.5 Range (mg/mi) 32.-116. 14.-36. LEVs are currently running only in California on low-sulfur fuel, so the emission factor using Indolene is the applicable one. Emissions were always higher with CAAB Fuel than with Indolene. In 8 cases, tests were repeated with both fuels. Six of the tests were with LEVs, and two with Tier 1 vehicles. All showed higher emissions with CAAB than with Indolene. The ratio of nitrous oxide emissions using CAAB to those using indolene ranged from 1.2 to 4.4 and averaged 2.6. The mean of the ratio was significantly larger than 1 (p<.01). We believe that the basis for this difference is fuel sulfur content. The fuel analyses and some modeling results supporting this belief are in Appendix B. Emissions were usually higher with A/C On at 95 °F than with A/C off at 75 °F In 22 cases, tests were repeated under both A/C modes. In seventeen cases emissions were higher with A/C on, in five cases with A/C off. The ratio of nitrous oxide emissions with A/C on to those with A/C off ranged from 0.9 to 3.4 and averaged 1.5. The mean of the ratio was significantly larger than 1 (p<.01). Nitrous Oxide was unrelated to the mileage of the vehicles. A regression of nitrous oxide emission factors against mileage for Tier 1 passenger vehicles yielded a slight positive slope not significantly different from zero (p<0.25). R2 was 0.06. N2Ovs. 0.15 -, | 0.10- O) £5 0.05 - 0.00 ( Tierl 4 ) 10000 20000 Mileage for CAAB Fuel Passenger Vehicles • :. • *• ; * 30000 40000 50000 60000 70000 80000 Mileage PageS ------- Barton and Simpson (1994) similarly did not find a significant relationship between nitrous oxide emissions and mileage. Their slope was negative. Light-duty trucks had higher emissions than passenger vehicles. This result is in agreement with Ballantyne et al. (1994) and with Barton and Simpson (1994). 3.3 Emission factors for gasoline highway vehicles other than passenger cars Only three of the reviewed studies include data on vehicles other than passenger vehicles. All the non-passenger vehicles were light duty trucks equipped with TWCs. The results are summarized in the following table: Study NVFEL Ballantyne et al. (1994) Barton and Simpson (1994) Age Old All Old New All Old New Emission factors (mg/mi) (number of vehicles) Light-duty trucks 109 (5) 188 (3) 93(1) 236 (2) 163 (3) 300(1) 95(1) Passenger vehicles 46 (12) 111(11) 126 (8) 74(3) 75(11) 80(11) 55(2) Average Trucks/PVs (ratio) 2.4 1.7 0.73 3.2 2.2 3.8 1.7 2.2 While the data are limited and not without exception, they are fairly convincing that light-duty trucks emit more nitrous oxide per mile than passenger vehicles. In the absence of a better alternative, we recommend that emission factors for passenger vehicles be applied to other gasoline highway vehicles in proportion to their fuel economy, which is the same practice employed in the Draft Inventory. For this purpose, we have used the fuel economies specified by Weaver and Chan (1996) and incorporated into the IPCC Guidelines. They are listed in Appendix C. According to Chan (1998), they were obtained from MOBILES and then reduced by 15%. The use of fuel-consumption ratios to determine emission factors should be considered a temporary measure only, to be replaced as soon as real data are available. 3.4 Recommended emission factors for gasoline highway vehicles Page 9 ------- Passenger vehicles A list of the revised emission factors is presented in Section 6.1. Except for LEVs as specified, it is assumed that these vehicles are being operated on a standard commercial fuel containing about 300 ppm sulfur. Aged TWCs emit more than new TWCs, but we believe aging happens fairly early, so we assume most of the fleet is aged. There are no data to assign a mileage to this transition. Control Technology Non-catalyst Oxidation catalyst TierO Tier 1 LEVs on standard fuel LEVs on low-S fuel Emission Factor (mg/mi) 16.6 51.7 81.5 46.3 77.8 28.3 n O 11 12 21 6 8 Std. Err. Mean (mg/mi) 13.0 19.1 13.8 5.0 14.7 2.5 Range (mg/mi) 2-42 8-233 6-190 24-124 32-116 14-36 Emission Factor (mg/km)* 10.3 32.2 50.7 28.8 48.4 17.4 * Extra precision has been included so conversion between units does not introduce a significant difference. Summary of Sources: Control Technology Non-catalyst Oxidation catalyst TierO Tier 1 LEVs on standard fuel Data Source Prigent and de Soete (1989), Dasch (1992), and Urban and Garbe (1979) Smith and Carey (1982), Urban and Garbe (1979) Smith and Carey (1982), Barton and Simpson (1994), and NVFEL (1998) (one car). Only old cars were included. Ballantyne et al. (1994) was excluded because of high fuel sulfur content (700 ppm). NVFEL (1998). CAAB fuel, both A/C modes. NVFEL (1998). CAAB fuel, both A/C modes. Page 10 ------- LEVs on low-sulfur fuel NVFEL (1998). Indolene fuel, both A/C modes. Gasoline highway vehicles other than passenger vehicles A list of the revised emission factors is presented in Section 6.1. We have used fuel-specific emission factors, as was done in the Draft Inventory. That is, we use the preceding emission factors for passenger vehicles, adjusted by the ratio of the fuel economies of passenger vehicles and the other vehicle type. The data that support this practice are that light trucks emit more nitrous oxide than passenger vehicles (see Section 3.3). The data are not good enough to say how much more, but fuel-specific emission factors seem an appropriate estimate at this time. The increasing proportion of light trucks in the U.S. fleet emphasizes the need to collect additional data. We have used the fuel economies in the IPCC Guidelines for calculating fuel-specific emission factors. These fuel economies came from MOBILES, reduced by 15% (Chan 1998). While it is likely that these estimates of fuel economy can be improved, it is only their ratios that are being used in this context. The use of fuel-consumption ratios to determine emission factors should be considered a temporary measure only, to be replaced as soon as real data are available. Note that for Gasoline Heavy-Duty Vehicles the emission factors in Table C-8 of the Draft Inventory specified as Catalyst and Non-Catalyst Control were actually the fuel-specific values for Advanced 3-Way and Early 3-Way. This error is also present in the IPCC Guidelines and in Weaver and Chan (1996). 4 OTHER ISSUES 4.1 Diesel emission factors Weaver and Chan (1996) cite Dietzmann et al. 1980 (SAE 801371) as the basis for nitrous oxide emission factors for heavy-duty diesel trucks, saying that they averaged the Dietzmann et al. values for heavy-duty trucks and estimated emission factors for lighter duty vehicles by assuming fuel-specific emission factors. Four engines were studied in Dietzman et al., one from 1977 and three from 1979. The 1979 engines were required to meet more stringent emissions standards. The average nitrous oxide emission factors for Dietzman et al.'s three 1979 engines were 31, 55, and 40 mg/mi. The 1977 engine emitted 76 mg/mi. The average of the four values is 50.5 mg/mi = 31.4 mg/km, which is the value Weaver and Chan use for uncontrolled HDD Vs. Fuel-specific emission factors seem to have been applied inconsistently to other diesel classes. For example, 63 mg/km is assigned to light-duty diesels with moderate control. Application of fuel-consumption proportionality yields emission factors of about 10 mg/km for light-duty trucks and 8 mg/km for passenger vehicles. The IPCC Guidelines values for European diesels (Tables 1-37 to 1-39) are 30, 20, and 10 mg/km for heavy-duty, light-duty, and passenger vehicles Page 11 ------- respectively. The values in Dietzmann, Weaver and Chan, and the European tables in the IPCC Guidelines are all quite low and in the same range. Because of very limited data and greater European experience with diesel, OMS recommends taking the European values from the IPCC Guidelines: 30, 20, and 10 mg/km for heavy-duty, light-duty, and passenger vehicles respectively. Vehicle type and control technology Diesel Passenger Cars Control Technology Advanced Moderate Uncontrolled Diesel Light Trucks Control Technology Advanced Moderate Uncontrolled Diesel Heavy-Duty Vehicles Control Technology Advanced Moderate Uncontrolled Draft Inventory (g/km) 0.0070 0.0100 0.0140 0.0240 0.0630 0.0310 0.0250 0.0250 0.0310 Fuel-specific based on Dietzmann et al. (1980) (g/km) 0.0068 0.0071 0.0091 0.0094 0.0095 0.0119 0.0283 0.0289 0.0314 European (g/km) 0.0100 0.0100 0.0100 0.0200 0.0200 0.0200 0.0300 0.0300 0.0300 4.2 Control technologies and their assignment by model year. A small section of Table C-7 of the Draft Inventory is shown below: U.S. Greenhouse Gas Emissions and Sinks: 1990-1996 Page 152 Table C-7: Control Technology Assignments for Highway Mobile Sources Vehicle Type/Technology Model Years Gasoline Passenger Cars and Light-Duty Trucks Uncontrolled 1966-1972 Non-catalyst controls 1973-1977 Oxidation catalyst 1978-1982 Early three-way catalyst 1983-1995 Three-way catalyst 1996 Low emission vehicle* 1996 The following control technology designations are more appropriate for U.S. vehicles: For "Early three-way catalyst," substitute "Tier 0." For "Three-way catalyst," which is referred to in Table C-8 (Emission Factors) as "Advanced 3 Way," substitute "Tier 1." Page 12 ------- See Section 1.1 above for additional discussion of this issue. Our revised assignment of technologies by model year are detailed in the tables in Section 6.2. Our principal source for this data is the "Compilation of Air Pollutant Emission Factors, Volume II: Mobile Sources" (U.S. EPA 1998), commonly referred to as AP42. Additional information concerning the phase-in of Tier 1 and LEV technologies and schedules for California have been provided by our MOBILE team. A significant change from the way the Draft Inventory technology assignments were done is the splitting of a single model year between more than one technology. We felt it was especially important to do this for later model years, which make up a large proportion of the fleet. The effect of our revisions is to introduce technologies earlier than they were introduced in the Draft Inventory. 4.3 Distribution of VMT by vehicle age for each calendar year The table of fraction of VMT by vehicle age that was used for all calendar years in the Draft Inventory is plotted in the figure below. Each vehicle type is plotted with a separate line. VMT splits by vehicle age, in Draft Inventory (mobile96.xls) Note: LDGV=LDDV and LDGT1=LDDT Age (years, 1=current model year) The irregularity of the plot indicates that these values represents data for a particular year. However, the spreadsheet used in the Draft Inventory applies this table to all years from 1990 to 1996. The table has a large peak for vehicles that are eleven years old, reflecting large purchases of new vehicles in that model year. When this table is applied to other years than the one for which the data apply, this peak will be incorrectly associated with other model years. As a matter of documentation, the year from which the data for this table were taken and the source of the data should be specified. Page 13 ------- 4.4 Uncertainty estimates Various places in the Draft Inventory contain discussions of uncertainty, but the Executive Summary and Annex C do not. The discussion of uncertainty on p. 27 should be repeated in both the Executive Summary and Annex C. The data in these locations otherwise give an impression of far greater precision than is warranted. 5 EFFORTS THAT WOULD IMPROVE FUTURE INVENTORIES 5.1 Measure the nitrous oxide emissions of in-use vehicles There is a great need for additional data. Nitrous oxide emissions from in-use vehicles should be measured in as many testing programs as possible. In programs where an FTIR is being used, adding the analysis of nitrous oxide should be relatively simple. Heavier gasoline vehicles should be tested to determine their emission factors. The light truck fleet is becoming a larger proportion of the U.S. total and therefore needs to be well characterized. The current stratagem of using fuel-specific emission factors is suitable only as a temporary measure. The effect of sulfur on nitrous oxide emissions should be studied, on different vehicle types, with and without catalysts. It appears that sulfur has a strong effect on nitrous oxide emissions. Emission factors for vehicles with TWCs may prove to be a strong function of the sulfur content of the fuel used. Diesel vehicles of all weight classes should be tested. Routine testing should include nitrous oxide. We need data on in-use vehicles, and, as new control technologies are developed, we will need data on how those technologies affect nitrous oxide emissions. The large variability in nitrous oxide emissions should be understood. Such knowledge might lead to changes in catalyst design and configuration that would eliminate high emitters. Second- by-second studies of low and high emitters would probably yield good insight into the problem, and provide some productive hypotheses for further testing. 5.2 Refine estimates of fleet composition and activity Separate tables of VMT fraction by vehicle age should be developed for each historical calendar year for which an inventory is prepared. VMT estimates could benefit from close scrutiny and comparison between sources. VMT and fuel-sales-based estimates should be reconciled. Page 14 ------- 5.3 Analyze additional sources in the literature While only further testing will provide the real data we need, some additional value can be obtained by a more exhaustive review of the literature. • Authors who tested vehicles using the FTP, but did not report the composite number we need for consistency, might be willing to supply that data if requested. For example: Laurikko and Paivi (1995) tested five cars of different mileages at different temperatures on the FTP cycle, but only reported bags 1 and 3. Joumard et al. (1996) tested 25 private cars, some with and some without catalysts, on a variety of driving cycles, including the FTP, but nitrous oxide was not reported for the FTP. • Careful analysis of European and Japanese driving cycles could possibly yield data comparable to those from the FTP cycle. 5.4 Develop estimates of uncertainty Estimates of uncertainty should be developed in future Inventories. 5.5 Include nitrous oxide as part of a future version of MOBILE Incorporating nitrous oxide into MOBILE would assure that our knowledge of nitrous oxide emissions by mobile sources is represented in a way consistent with other mobile emissions. It would also simplify the generation of an annual inventory. 5.6 Integrate with the Trends process The estimates of nitrous oxide emissions from mobile sources should be integrated with the process by which OAQPS produces the National Air Pollutant Emission Trends Data Base. This approach would avoid duplication of effort and improve consistency across EPA. 6 CONSOLIDATED LIST OF SPECIFIC CHANGES TO THE DRAFT INVENTORY 6.1 Revised nitrous oxide emission factors for highway mobile sources The following table lists the revised emission factors. It corresponds to Table C-8 in Annex C of the Draft Inventory. The rationale for these emission factors is detailed in the body and appendices of these comments. We have included more significant figures than is warranted by their uncertainty to assure consistent calculations when using different units. Note that instead of Page 15 ------- "Early" and "Advanced" TWCs, we use the terms "Tier 0" and "Tier 1". Vehicle type and control technology Gasoline Passenger Cars Control Technology Low Emission Vehicles* Tierl TierO Oxidation Catalyst Non-Catalyst Uncontrolled Nitrous Oxide Emission Factors g/mi 0.0283 0.0463 0.0815 0.0517 0.0166 0.0166 * Applicable to California VMT only Gasoline Light-Duty Trucks Control Technology Low Emission Vehicles* Tierl TierO Oxidation Catalyst Non-Catalyst Uncontrolled * Applicable to California VMT only Gasoline Heavy-Duty Vehicles Control Technology TierO Oxidation Catalyst Non-catalyst Uncontrolled Diesel Passenger Cars Control Technology Advanced Moderate Uncontrolled Diesel Light Trucks Control Technology Advanced Moderate Uncontrolled Diesel Heavy-Duty Vehicles Control Technology Advanced Moderate Uncontrolled Motorcycles Control Technology Non-Catalyst Control Uncontrolled 0.0400 0.0643 0.1362 0.0673 0.0188 0.0190 0.2781 0.1400 0.0412 0.0432 0.0161 0.0161 0.0161 0.0322 0.0322 0.0322 0.0483 0.0483 0.0483 0.0068 0.0087 g/km 0.0176 0.0288 0.0507 0.0322 0.0103 0.0103 0.0249 0.0400 0.0846 0.0418 0.0117 0.0118 0.1729 0.0870 0.0256 0.0269 0.0100 0.0100 0.0100 0.0200 0.0200 0.0200 0.0300 0.0300 0.0300 0.0042 0.0054 6.2 Revised technology assignments by model year for gasoline highway vehicles except Page 16 ------- motorcycles For Gasoline Passenger Cars (light duty gas vehicles. LDGVX except California: Model Year <1972 1973-1974 1975 1976-1977 1978-1979 1980 1981 1982 1983 1984-1993 1994 1995 1996 Percentage of 49 States LDGV with each control technology Uncontrolled 100 Non-catalyst control 100 20 15 10 5 Oxidation 80 85 90 88 15 14 12 TierO 7 85 86 88 100 60 20 Tier 1 40 80 100 Page 17 ------- For Gasoline Light Duty Trucks (LDGTX except California: Model Year <1972 1973-1974 1975 1976 1977-1978 1979-1980 1981 1982 1983 1984 1985 1986 1987-1993 1994 1995 1996 Percentage of 49 States LDGT with each control technology Uncontrolled 100 Non-catalyst control 100 30 20 25 20 Oxidation 70 80 75 80 95 90 80 70 60 50 5 TierO 5 10 20 30 40 50 95 60 20 Tier 1 40 80 100 For Gasoline Heavy-Duty Vehicles (heavy-duty gas vehicles. HDGV): Model Year <1981 1982-1984 1985-1986 1987 1988-1989 1990-2003 2004 Percentage of national HDGV with each control technology Uncontrolled 100 95 Non-catalyst control 95 70 60 45 Oxidation 5 5 15 25 30 TierO 15 15 25 100 Page 18 ------- For California Gasoline Passenger Cars and Light-Duty Trucks (light duty gas vehicles and trucks. LDGV and LDGTI: Model Year <1972 1973-1974 1975-1979 1980-1981 1982 1983 1984-1991 1992 1993 1994 1995 1996 Percentage of California LDGV and LDGT fleet with each control technology Uncontrol led 100 Non- catalyst control 100 Oxidation 100 15 14 12 Tier 0 85 86 88 100 60 20 Tier 1 40 80 90 85 80 LEV 10 15 20 6.3 Document distribution of VMT by vehicle age for each calendar year The existing table of VMT by vehicle age is for a particular but unspecified year. As a matter of documentation, the year from which the data for this table were taken and the source of the data should be specified. 6.4 Include a discussion of uncertainty in the Executive Summary and Annex C Various places in the Draft Inventory contain discussions of uncertainty, but the Executive Summary and Annex C do not. The discussion of uncertainty on p. 27 should be repeated in both the Executive Summary and Annex C. The data in these locations otherwise give an impressions of far greater precision than is warranted. 7 REFERENCES Ballantyne, Vera F., Peter Howes, and Leif Stephanson. 1994. "Nitrous Oxide Emissions from Light Duty Vehicles." SAE Paper 940304. Page 19 ------- Barton, Peter and Jackie Simpson. 1994. "The effects of aged catalysts and cold ambient temperatures on nitrous oxide emissions." Mobile Sources Emissions Division (MSED), Environment Canada, MSED Report #94-21. Braddock, James N. 1981. "Impact of low ambient temperature on 3-way catalyst car emissions." SAE paper 810280. Chan, Lit-Mian. 1998. Phone call July 23. Dasch, Jean Muhlbaler. "Nitrous Oxide Emissions from Vehicles." January, 1992. Journal of the Air and Waste Management Association, 42(1): 63-67. De Soete, Gerard G. 1993. "20. Nitrous oxide from combustion and industry: chemistry, emissions and control." In A. R. van Amstel (ed.) Proceedings of an InternationalIPCC Workshop on Methane and Nitrous Oxide : Methods in National Emissions Inventories and Options for Control. RIVM Report No. 481507003, Bilthoven, The Netherlands. De Soete, G. 1989. "Updated evaluation of nitrous oxide emissions from industrial fossil fuel combustion," draft final report prepared for the European Atomic Energy Community, Institut Francais du Petrole, Ref 37-559. Dietzmann, Harry E., Mary Ann Parness, and Ronald L. Bradow. 1980. "Emissions from Trucks by Chassis Version of 1983 Transient Procedure." SAE Paper 801371. IPCC/UNEP/OECD/IEA. 1997. Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories. Paris: Intergovernmental Panel on Climate Change, United Nations Environment Programme, Organization for Economic Co-Operation and Development, International Energy Agency. Jaques, A. P. 1992. Canada's Greenhouse Gas Emissions: Estimates for 1990. Environmental Protection Series, Report EPS 5/AP/4, December 1992. Environmental Protection, Conservation and Protection, Environment Canada. Joumard, Robert, Robert Vidon, Laurent Paturel, and Gerard de Soete. 1996. "Changes in pollutant emissions from passenger cars under cold start conditions." SAE Paper 961133. Laurikko, Juhani and Paivi Aakko. 1995. "The effect of ambient temperature on the emissions of some nitrogen compounds: a comparative study on low-, medium- and high-mileage three-way catalyst vehicles." SAE paper 950933. Lindhjem, Christian E. 1995. "The effect of gasoline reformulation and sulfur reduction on exhaust emissions from post-1983 but pre-1990 vehicles." SAE paper 950778. Lindskog, A. 1988. Data presented at the EPA/IFP European Workshop on the Emission of Page 20 ------- Nitrous Oxide from Fossil Fuel Combustion, Figures 5-18 and 5-19. Rueil-Malmaison, France, June 1-2, 1988. EPA Report EPA/600/13. Monroe, David R., Martin H. Krueger, Donald D. Beck and Michael J. D'Aniello, Jr. 1991. "The effect of sulfur on three-way catalysts." in A. Crucq (Editor), Catalysis and Automotive Pollution Control //, proceedings of the Second International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990. New York: Elsevier Science Publishers. Neitzert, Frank. 1998. Personal communication. Prigent, M., G. de Soete, and R. Doziere. 1991. "The effect of aging on nitrous oxide N2O formation by automotive three-way catalysts," in A. Crucq (Editor), Catalysis and Automotive Pollution Control //, proceedings of the Second International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990. New York: Elsevier Science Publishers. Prigent, Michel and Gerard De Soete. 1989. "Nitrous oxide N2O in engines exhaust gases—a first appraisal of catalyst impact." SAE Paper 890492. Prigent, M. and G. G. De Soete. 1992. "The increase of N2O emissions caused by three-way automotive catalysts." NIRE/IFP/EPA/SCEJ 5th Interrnational Workshop on N2O Emissions, 1-3 July 1992, Tsukuba, Japan, paper 10-3. We do not have this document. Data from it is referenced in de Soete (1993). Smith, L. R. and F. M. Black. 1980. "Characterization of exhaust emissions from passenger cars equipped with three-way catalyst control systems." SAE paper 800822. Smith, Lawrence R. and Penny M. Carey. 1982. "Characterization of exhaust emissions from high mileage catalyst-equipped automobiles." SAE paper 820783. Urban, Charles M. and Robert J. Garbe. 1979. "Regulated and Unregulated Exhaust Emissions from Malfunctioning Automobiles." SAE Paper 79696. Urban, Charles M. and Robert J. Garbe. 1980. "Exhaust Emissions from Malfunctioning Three- Way Catalyst-Equipped Automobiles." SAE Paper 800511. U.S. EPA. 1997. The 1997 U.S. Climate Action Report, Submitted by the United States of America Under the United Nations Framework Convention on Climate Change. U.S. EPA. 1998. Inventory of U.S. Greehouse Gas Emissions and Sinks 1990-1996. Draft, 3/10/98. U.S. EPA, Office of Policy, Planning, and Evaluation. EPA-230-R-97-002. U.S. EPA. 1998. "Compilation of Air Pollutant Emission Factors, Volume II: Mobile Sources," Page 21 ------- commonly referred to as AP-42, pending 5th edition, last updated: 06 April 1998. Accessed from the web site: http://www.epa.gov/omswww/ap42.htm. U.S. EPA. 1989. "EPA/IPF European Workshop on the emission of nitrous oxide from fossil fuel combustion (Rueil-Malmaison, France)," Prepared by Air and Energy Engineering Research, Research Triangle Park, Raleigh, North Carolina, Report No. EPA-600/9-89- 089. Weaver, Christopher S., Lit-Mian Chan. 1996. "Mobile source emission factors for global warming gases." Draft Final Report, June 24, 1996, submitted to ICF, Inc., 1850 K Street, NW, Suite 1000, Washington DC by Engine, Fuel, and Emissions Engineering, Inc., 9812 Old Winery Place, suite 22, Sacramento, CA 95827. Weaver, Christopher S. 1998. Telephone conversation on July 10. Page 22 ------- APPENDIX A A DETAILED DISCUSSION OF THE ORIGIN OF THE EMISSION FACTORS FOR NITROUS OXIDE FOR GASOLINE HIGHWAY VEHICLES IN THE DRAFT INVENTORY The following sections detail the number trail backward from the Draft Inventory to original sources, supporting the more limited description in the body of the comments. A. The Draft Inventory, the IPCC Guidelines, Weaver and Chan (1996). The Draft Inventory lists emission factors that are identical to those of the IPCC Guidelines., which in turn are identical to those of Weaver and Chan (1996), who are the source of these values (Weaver 1998). For light-duty passenger gasoline highway vehicles, the emissions factors are as follows: Low Emission Vehicles Advanced 3 Way Early 3 -way Oxidation Catalyst Non-Catalyst Uncontrolled U.S. Draft Inventory , Calca g/km . . g/mi 0.04 .064 0.17 .274 0.17 .274 0.075 .121 0.02 .032 0.02 .032 IPCC Guidelines g/kg 0.453 1.892 1.81 0.622 0.125 0.13 km/L g/km 8.5 8.3 8 6.2 4.5 4.7 a Calculated from g/km by conversion factor for km/mi b Calculated from g/kg using km/L and 0.75kg/L c Calculated from the calculated g/km by conversion factor for 0.040 0.170 0.170 0.075 0.020 0.020 km/mi Calcb g/km 0.04 0.171 0.17 0.075 0.021 0.021 Calcc g/mi 0.064 0.275 0.273 0.121 0.034 0.033 The calculations in this table have been done to verify the internal consistency of the emission factors expressed in different units in the IPCC Guidelines and to examine how the precision shown affects the interconversion of units. The emission factors listed as g/km in the Draft Inventory are identical to the factors listed as g/km in the IPCC Guidelines. The tables of emission factors in the IPCC Guidelines are identical to those in Weaver and Chan (1996). B. From Ballantyne et al. (1994) to Weaver and Chan (1996) Weaver and Chan (1996) got their emission factors from the last column of Table 7 in Ballantyne Page A-l ------- et al. (1994), headed "Current Canadian Estimates: EPS Inventory:" Comparison of control -technology terminology and emission factors between Ballantyne et al. (1994) and Weaver and Chan (1996) Ballantyne (1994) Table 7 Catalyst Type New 3 -way Aged 3 -way Oxidation None Current Canadian Estimates: EPS Inventory (mg/mi) 60 280 120 32 Units conversion to (g/km) .037 .174 .075 .020 Weaver and Chan (1996) Control Technology LEV Early 3 -Way, Three-way Oxidation Uncontrolled, Non-Catalyst Emission Factor (g/km) 0.040 0.170 0.075 0.020 Of the four sets of estimates in Ballantyne et al.'s Table 7, the reason for choosing this one, according to Weaver (1998), was the wide range of the estimates, the difficulty of reconciling them, and the fact that the Canadian emission factors appeared to be official government figures. Weaver and Chan (1996) assumed both advanced and early TWCs to have the same nitrous oxide emissions properties. Weaver (1998) indicated that since catalyst aging occurs relatively quickly, all TWCs were assumed to be aged. He further indicated that he and Chan reasoned that LEVs would behave like new TWCs, because part of LEV technology was fine tuning catalyst placement and other factors to insure quick light-off, and that the aging effect was likely due to delayed light-off. Therefore LEVs would behave like new TWC vehicles. C. From Jaques (1992) to Ballantyne et al. (1994) The last column of Ballantyne et al.'s Table 7 originated, with some modification, from Canada's Greenhouse Gas Emissions: Estimates for 1990 (Jaques 1992). Ballantyne et al. appear to have converted Jaques's units (g/kg) into g/mi by using the fuel economies in Jaques's Table 16 and assuming a fuel density of 0.75 kg/L (Jaques's Table 32), as we show in the following table: Page A-2 ------- Jaques (1992) Catalyst Type Table 3 1 (g/kg) New 0.6 Aged 2.2 Ox 0.6 None 0.31 Table 16 „ , Table 3 1/ Fuel „ , , „ Table 16 Economy , ... (km/L) (mg/mi) 11.9 61 9.4 282 6 121 6 62 Ballantyne et al. (1994) Table 7 Current Canadian Estimates (mg/mi) 60 280 120 32 A problem with this derivation is that it produces 62 mg/mi for non-catalyst vehicles, but Ballantyne et al. list 32 mg/mi. The table below shows the column of Ballantyne's Table 7 giving the range of de Soete's (1989) estimates. We have produced the last column below (Actual Ranges) directly from de Soete's (1989) Table XIV. Catalyst Type New Aged Ox None Ballantyne et al. Current Canadian Estimates (mg/mi) 60 280 120 32 (1994), Table 7 de Soete, 1989 Range (mg/mi) 60-170 260-355 120 8-32 de Soete's (1989) Actual Ranges trom lable XIV all points lines 2,4-7, 11-19 (mg/mi) 54-141 50-1000 112-257 13-151 Ballantyne et al.'s listing of de Soete's (1989) ranges suggest that they took what they understood to be the high end of the non-catalyst range rather than the value provided by Jaques (1992), and mis-attributed it to Jaques. However, the last column of the above table shows de Soete's (1989) actual ranges as well as we have been able to determine them. One could suppose that Ballantyne et al. excluded outlier values, but the high end of Ballantyne et al.'s (1994) new TWC range and the low end of their non-catalyst range lie outside the actual ranges. Ballantyne, in an email through Stephanson (one of Ballantyne's co-authors), was unable to recall the origin of the non-catalyst emission factor. Another problem in using the last column in Ballantyne et al.'s Table 7 to represent the Current Canadian Estimates is that Jaques derived his emission factors from g/km data in de Soete (1989) and converted them to g/kg by assuming a uniform fuel economy of 8.5km/L (Neitzert 1998). Ballantyne et al. then converted these numbers (except for the non-catalyst case) to units of g/mi Page A-3 ------- by assuming a different set of fuel economies. The following table compares Ballantyne et al.'s "Current Canadian Estimates" to Jaques's, using the same fuel economy he assumed in deriving them. Catalyst Type New Aged Ox None Ballantyne et al. (1994) Current Canadian Estimates (mg/mi) 60 280 120 32 Jaques (1992) assuming 8.5km/L (mg/mi) 85 312 85 44 D. From de Soete (1989) to Jaques (1992) The official Canadian estimates for 1990 (Jaques 1992) have been derived primarily from de Soete (1989). Neitzert (1998) said that the emission factors in Jaques (1992) for new TWC, aged TWC and non-catalyst vehicles were obtained by averaging lines one and two of Table XXIX (de Soete 1989) and assuming a fuel economy of 8.5 km/L and a fuel density of 0.75kg/L. The following table demonstrates this derivation and also shows emission factors in g/km and g/mi: line 1, Table XXIX (gN/km) line 2, Table XXIX (gN/km) line 1, Table XXIX (gN2O/km) line 2, Table XXIX (gN2O/km) line 1, Table XXIX (gN2O/mi) line 2, Table XXIX (gN2O/mi) avg of lines 1 and 2 (gN2O/km) avg of lines 1 and 2 (gN2O/mi) Assuming 8.5km/L,.75kg/L (gN2O/kg) Jaques (1992), Table 31 (gN2O/kg) Uncontrolled 0.026 0.008 0.041 0.013 0.066 0.021 0.027 0.044 0.307 0.31 New TWC 0.03 0.037 0.048 0.059 0.077 0.095 0.053 0.086 0.604 0.6 Aged TWC 0.137 0.11 0.216 0.173 0.347 0.278 0.194 0.313 2.201 2.2 Comparison of the last two lines shows that we have successfully reproduced Jaques's emission factors, except for the oxidation catalyst case. Next, we must ask where Jaques's oxidation catalyst emission factor of 0.6 g/kg originated. De Soete's Table XXIX is a summary table for his Table XIV, which lists five emission factors for Page A-4 ------- vehicles equipped with oxidation catalysts. The average of these is 0.092 g/km, which converts to 1.04 g/kg and does not match Jaques's emission factor. We believe the most plausible explanation of Jaques's oxidation catalyst emission factor is that, in the absence of data lower than the new TWC data, it was simply taken to be identical to the new TWC emission factor. Neitzert (1998) did not know how the oxidation catalyst emission factor was derived. In the next section, we examine the original data sources. E. De Soete's (1989) original sources The averages in lines 1 and 2 of Table XXIX are referenced to lines 2, 4-7, and 11 of Table XIV. Each of the Table XIV lines referenced is actually a series of individual data points. Below are lines 1 and 2 of de Soete's Table XXIX: Emission factor (gN2OasN/km) Averaged over all cycles: ECE cold, ECE hot, EUDC and SDC (Table XIV, lines 2,4 to 7, 11 to 19) Averaged over all cycles: ECE cold, ECE hot and EUDC (Table XIV, lines 1 1 through 19) Uncontrolled (without catalyst) 0.0261 0.0084 With Three-Way Catalyst New 0.0304 0.0374 Aged 0.1373 0.1099 Note that the values in this table are averaged over European driving cycles only. There are a few FTP cycles included in Table XIV, but they are not included in the averages in Table XXIX. Below, we have attempted to replicate Table XXIX by averaging the specified lines in Table XIV: Lines of Table XIV used in average 2,4 to 7, 11 to 19 11 to 19 2,4 to 7 Lines 2 & 3 of this table Uncontrolled (without catalyst) 0.0236 0.0085 0.0284 0.0184 With Three-Way Catalyst New 0.0355 0.0374 0.0292 0.0333 Aged 0.1177 0.11 0.1486 0.1293 We have succeeded in replicating line 2 of Table XXIX, but not line 1. Page A-5 ------- This table shows the data sources contributing to Jaques (1992). Table XIV is in de Soete (1989). Data Source Table XIV, line 2 Table XIV, lines 4-7 Table XIV, lines 11-19 Total Data Points for3 no cat. 6 24% 1 13 52% 2 6 24% 1 25 new TWC 15 24% 48 76% 63 aged TWC 6 20% 1 24 80% 30 ox cat. 0 Reference13 42. Lindskog, A., data presented at the EPA/IFP Workshop 1988, report on that meeting p. 103 and tables 5-18 and 5-19. 43, see also 44 and 45. 43. Prigent, M., Doziere, R. and De Soete, G., unpublished document of the French Petroleum Institute, 1988. 44. Prigent, M., data presented at the EPA/IFP Workshop 1988, p. 103-109 and figs 5-7 and 5-8 45. Prigent, Michel and Gerard De Soete. 1989. "Nitrous oxide N2O in engines exhaust gases— a first appraisal of catalyst impact. " SAE Paper 890492. 47. Prigent, M.F., de Soete, G.G. and Doziere, R., "The effect of catalyst aging on nitrous oxide emissions from automobiles with a three-way catalyst," to be presented at the CAPoC Meeting, Brussels, 10-13 September 1990. a. Top number is the number of data points. The next number is the percentage of total data points that reference comprises for the control category. The third number is the number of vehicles tested. If there is only one vehicle number in a row, the same vehicle or vehicles were used to test all control technologies. b. The numbers are those used in Table XIV to indicate the references. 42. Lindskog 1988 reported on two cars on the SDC (Swedish driving cycle), a Volvo 240 without a catalyst, and a Volvo 260 with 10,000 km with a TWC. 45. Prigent and de Soete. 1989. "Nitrous oxide N2O in engines exhaust gases—a first appraisal of catalyst impact." SAE Paper 890492 is apparently the same material presented at the EPA/IFP Workshop in 1988. Two cars were tested, a Citroen BX19GT and a Renault Fuego U.S. version, Page A-6 ------- with and without TWCs. 47. Prigent, M., G. de Soete, and R. Doziere. 1991. "The effect of aging on nitrous oxide N2O formation by automotive three-way catalysts," in A. Crucq (Editor), Catalysis and Automotive Pollution Control II, proceedings of the Second International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990. New York: Elsevier Science Publishers. These tests were performed using 8 different catalysts and two similar 2.2L 4 cylinder engines. One was for aging the catalysts, the other, mounted in an unspecified chassis, was used for running the tests. The catalysts were mounted 1.4m from the engine. They were not production catalysts but apparently were fabricated for these tests. This reference gives measurements in g/test graphically and ratios between catalyst and non-catalyst vehicles numerically. However, the individual test results in g/km are given in Table XIV of de Soete (1989). The test vehicle and engine are unidentified in the reference, but are identified in Table XIV as a "Fuego, 2.21 L engine equipped with electronic fuel injection + oxygen sensor, closed loop." A subsequent publication by the same researchers apparently involving a different vehicle and the same or a similar set of new and aged catalysts, gives sharply lower nitrous oxide emission factors: the averages were 12 mg/mi for non-catalyst vehicles, 29 mg/mi for new TWCs, and 42 mg/mi for aged TWCs (Prigent and de Soete 1992). These are lower than their previously reported values by factors of approximately 4, 3, and 7, respectively. F. Summary of the data sources • All the emission factors originate from testing done on five cars using European test cycles. Fuel sulfur content for these tests was unspecified. • The new and aged TWC emission factors are based 90% on a single study using a single car with eight non-production catalysts, new and bench-aged, with the catalysts located 1.4 m from the engine. The other 10% of the data for the TWC emission factors came from two studies and three more cars, all tested on European driving cycles only. • The non-catalyst emission factors were derived from four cars. • The emission factor for oxidation catalyst vehicles does not appear to be based on testing, but is instead the same emission factor used for new TWCs. Page A-7 ------- APPENDIX B NVFEL TESTING PROGRAM SUMMARY TABLE OF PRELIMINARY NVFEL TESTING RESULTS. Nitrous oxide emissions are shown in grams per mile for the composite FTP cycle. CAAB is the Clean Air Act Baseline Fuel, which contained 285 ppm sulfur. Indolene contained 24 ppm sulfur. PV = passenger vehicle MV = mini-van PU = pickup truck SUV = sport utility vehicle Vehicle Type PV MV PV MV MV PV PV PV PV MV PU PU PU PU PU MV PV PV SUV PV MV PV MV Odometer (miles) 75698 39539 48690 23914 27491 47461 38766 75083 24086 23838 26262 41549 20585 16319 19251 32818 28935 41896 20949 4959 169311 * 5038* 5038* Emissions Control TierO TieM Tierl TieM Tierl Tierl Tierl Tierl Tierl Tierl Tierl Tierl Tierl Tierl Tier 1 Tierl Tierl Tierl Tierl LEV LEV LEV LEV CAAB Fuel 75° F A/COff 0.018 0.046 0.059 0.038 0.028 0.027 0.036 0.042 0.024 0.027 0.227 0.167 0.082 0.087 ** ** ** 95° F A/C On 0.053 0.067 0.124 0.033 0.049 0.035 0.054 0.052 0.081 0.029 0.203 0.145 0.082 0.102 0.080 0.043 0.033 0.046 0.126 ** ** ** Indolene Fuel 75° F A/C Off 0.115 0.063 ** ** ** ** 95° F A/C On 0.039 ** ** ** ** * Catalyts bench-aged to 100,000 miles. ** Data not shown here, but included in averages. PageB-1 ------- ANALYSES OF THE FUELS USED IN NVFEL TESTING Tested at NVFEL CAAB Dispen. #2: tests conducted between 6/4 and 6/15/98 tank #21 cert (Indolene): tests conducted between 2/26 and 3/16/93 Test Code 552 562 534 572 421 62 65 66 48 49 64 46 69 692 691 101 110 150 190 200 201 202 203 592 541 591 543 585 589 5802 593 59 30 32 991 73 221 220 218 Test method MTBE by OFID ETBE by OFID EthanolbyOFID TAME by OFID Sulfur in Gasoline by ASTM D 2622 Vapor Pressure by Appendix E Method 3 Percent Evaporated at 200 Degrees F Percent Evaporated at 300 Degrees F Aromatics in Gasoline MSD D5769 Olefinsin by FIA D-1319-93 Benzene in Gasoline by ASTM D 3606 Aromatics by FIA D-1319-93 Specific Gravity @ 60 Degrees F Degrees API Density @ 60 deg F D 86 Initial Boiling Point 1 0 Percent 50 Percent 90 Percent End Point Residue Total Recovery Loss Volume Percent Oxygenates by MSD Methanol by MSD (Screen) Weight Percent Oxygen by MSD Methanol by OFID t-Butanol by OFID Isobutanol by OFID n-Butanol by OFID Volume Percent Oxygenates by OFID Weight Percent Oxygen by OFID Lead in Gasoline by ASTM D 3237 Weight Fractioin Carbon ASTM D 3343- 95 Phosphorus in Gasoline by ASTM D 3231 Net Heat of Combustion ASTM D 3338-92 Motor Octane Research Octane Sensitivity CAAB 0.099 0 0 0 285 7.44 39.5 80.5 38.261 8.524 1.22 30.6 0.75352 56.28 0.75278 98.8 139.69 222.6 338.89 413.89 1.89 96.8 1.29 0.55 0 0.1 0 0 0 0 0.55 0.09 0.001 0.8673 0 18428 82.59 92.09 9.5 Indolene 0 0 0 0 24 9.02 36.4 88.3 49.437 1.053 0.2409 30.1 0.74397 58.69 0.74324 92.8 132.39 219.8 315.79 381.7 1 97.69 1.29 0 0 0 0 0 0 0 0 0 na 0.8661 na na na na na UNITS Oxy Percent Oxy Percent Oxy Percent Oxy Percent Parts Per Million PSIA Volume Percent Volume Percent Volume Percent Volume Percent Volume Percent Volume Percent 60/60F Degrees API g/cm-03 @ 60 deg F Degrees F Degrees F Degrees F Degrees F Degrees F mL mL mL Volume Percent Volume Percent Weight Percent Volume Percent Volume Percent Volume Percent Volume Percent Volume Percent Weight Percent Grams Pb per Gallon Weight Fraction Grams per Gallon BTU per Pound Motor Octane Number Research Octane Number RON-MON na = not analyzed Page B-2 ------- WHY WE BELIEVE THE NITROUS OXIDE DIFFERENCES BETWEEN THE TWO FUELS ARE DUE TO DIFFERENCES IN SULFUR CONTENT In the NVFEL testing program, emissions of nitrous oxide average 2.5 times higher using CAAB fuel than using Indolene. There are many differences between these two fuels, as the previous table shows. In this section, we make our case—suggestive, rather than conclusive—that the difference in nitrous oxide emissions is primarily due to the difference in the sulfur content of the fuels. The argument may be summarized that TWCs emit nitrous oxide when they are performing less efficiently than normal (e.g., at lower than normal operating temperatures or after aging), when they also emit more NOX. Sulfur decreases the efficiency of TWCs and increases NOX emissions. Therefore, sulfur is also likely to increase nitrous oxide emissions. Of the differences between CAAB fuel and Indolene, modeling shows that only sulfur accounts for the increased NOX emissions of CAAB fuel. Therefore, that same difference probably also accounts for the increased nitrous oxide emissions. We know of no published testing on the effects of sulfur content or other fuel parameters on nitrous oxide emissions. However, existing data suggest that for cars equipped with TWCs, conditions that enhance NOX emissions (i.e., decrease the effectiveness of the catalyst) also enhance nitrous oxide emissions. For example: 1. Nitrous oxide emissions are maximal at around the light-off temperature of catalysts, when NOX conversion is suboptimal (Prigent et al. 1991). 2. For the same cars equipped with TWCs, tuneups decrease both NOX and nitrous oxide emissions (Smith and Carey 1982). 3. Running the FTP at a lower than normal temperature in two cases increased NOX emissions and in two cases decreased them. In all cases the change in nitrous oxide emissions was in the same direction as the change in NOX emissions (Braddock 1981). Sulfur has been shown to decrease the effectiveness of NOX conversion (Lindhjem 1995, Monroe etal. 1991). Also, we have received an email from Matthias Tappe of the German Federal Environmental Agency - Environment and Traffic as follows: "Regarding the sulfur content your idea that the sulfur level in gasoline influences the N2O emissions has been confirmed by industry data available to us." EPA's Complex Model shows that the sulfur difference between CAAB and Indolene is the only difference that strongly affects NOX emissions EPA's Complex Model was developed in conjunction with petroleum refiners and gasoline formulators to provide guidance as to how emissions would change when various gasoline components were altered. The model predicts that our CAAB fuel will emit 13% more NOX than Page B-3 ------- our Indolene fuel. The first column in the following table lists the components used by the Complex Model that are different between CAAB and Indolene. The second column shows the percentage change in NOX emissions that results when the component in the first column is changed from its value in Indolene to its value in CAAB. The third column shows the percentage change in NOX emissions when all components except the one in the first column are changed from their Indolene to their CAAB values. Parameter All parameters MTBE Sulfur RVP E200 E300 Aromatics Olefins Benzene Percentage change in NOX emissions from Indolene when: Only this parameter is changed to its CAAB value 13 0 12 0 0 0 0 1 0 All parameters except this one are changed to their CAAB values 0 13 1 13 13 12 13 12 13 Sulfur is the parameter of greatest importance in diminishing the catalytic reduction of NOX, and, therefore, we suspect, also the parameter of greatest importance in enhancing the production of nitrous oxide. Page B-4 ------- APPENDIX C ASSUMED FUEL ECONOMIES WHOSE RATIOS WERE USED TO GENERATE EMISSION FACTORS FOR VEHICLES FOR WHICH THERE WERE NO DATA The following of fuel economies and carbon dioxide emission factors are from Tables 1-27 through 1-33 of the IPCC Guidelines. The source of these tables is Weaver and Chan (1996). Chan (1998) said that their source for fuel economies was MOBILES reduced by 15%. The use of fuel-consumption ratios to determine emission factors should be considered a temporary measure only, to be replaced as soon as real data are available. In calculating emission factors, we used the ratios of carbon dioxide emission factors, rather than of fuel economies, because they were listed with more significant digits. The two are equivalent within rounding error, as is shown by the third column of the table below, which was obtained by multiplying the first two columns together. Vehicle type and control technology Gasoline Passenger Cars Control Technology Low Emission Vehicles* Tierl TierO Oxidation Catalyst Non-Catalyst Uncontrolled * Applicable to California VMT only Gasoline Light-Duty Trucks Control Technology Low Emission Vehicles* Tierl TierO Oxidation Catalyst Non-Catalyst Uncontrolled * Applicable to California VMT only Gasoline Heavy-Duty Vehicles Control Technology TierO Oxidation Catalyst Non-catalyst Uncontrolled Diesel Passenger Cars Control Technology Advanced Moderate Uncontrolled Diesel Light Trucks Control Technology Fuel EC (km/L) 8.5 8.3 8 6.2 4.5 4.7 6 6 4.8 4.8 4 4.1 2.3 2.3 1.8 1.8 10 9.6 7.5 C02 (g/km) 280 285 298 383 531 506 396 396 498 498 601 579 1017 1036 1320 1320 237 248 319 Test C02*Fuel EC (9/L) 2380 2366 2384 2375 2390 2378 2376 2376 2390 2390 2404 2374 2339 2383 2376 2376 2370 2381 2393 Page C-l ------- Vehicle type and control technology Advanced Moderate Uncontrolled Diesel Heavy-Duty Vehicles Control Technology Advanced Moderate Uncontrolled Motorcycles Control Technology Non-Catalyst Control Uncontrolled Fuel EC (km/L) 7.2 7.2 5.7 2.4 2.4 2.2 10.8 8.9 CO2 (g/km) 330 331 415 987 1011 1097 219 266 Test C02*Fuel EC (9/L) 2376 2383 2366 2369 2426 2413 2365 2367 Page C-2 ------- |