1 **U NITED STA** 

**TES ENVIRONMENTA L PROTECTION A** **GENCY** NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWO OD ROAD ANN ARBOR, MI 48105 May 4, 20 12 OFFICE OF AIR AND RADIATION MEMORANDUM SUBJECT: PM Emissions Impacts FROM: Lauren Steele, Office of Transportation and Air Quality TO: Docket EPA
- HQ
- OAR
- 2011
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### E **stimate of Particulate Matter Emissions from**  **Regulated Emergency Vehicles**  The Heav y - Dut y Highway R ule was projected to reduce direct particulate matter ( PM ) exhaust emissions from the heav y- dut y on - road fleet b y 71 ,000 tons in 20 2 0 , and by 96 ,000 tons in 20 3 0. Inthat rule’s final Regulatory Impact Analy sis, EPA projected that in 2010 the control led heav y - duty

fleet would emit approximately 57,000 tons of direct exha ust PM emissions, decreasing to 15,000 tons in 2020 and 8,000 tons direct PM exhaust in 2030, as a result of that rule. 1 For purposes of this memo, we are considering that rule’s control case as the current fleet baseline scenario. As noted in Section VII .B of the proposed rule preamble, c lass 3 through 8 fire apparatus and ambulances represent about 0.8 percent of annual new heavy
- dut y truck registrations. 2 If we assume these vehicles have the same emissions profile over time as other vehicles , we could estimate that their annual emiss ions collectively may also represent a comparable fraction of the fleet emissions in a given year. For the ye ars projected in the RIA for the H eav y - D uty Highway R ule , this would indicate emergency vehicles may have emitted on the order of 5 00 tons direct exhaust PM in 2010, may emit about 1 00 tons in 2020 , and may emit about 6 0 tons in 2030. However, we have information that these vehicles have longer than average useful lives, leading to a slower fleet turnover rate. We al so have information that these vehicles have below average vehicle miles traveled, with a large fraction of their engine hours at low load or idle. While these two factors would affect the emissions inventory in opposite directions, they are

1 Final Regulatory Impact Analysis for the “ 2007 Heavy
- Duty Highway Rule ,” EPA420
- R
- 00
- 026, December 2000 , Chapter II Health and Welfare Concerns and Emissions Benefits, Table II.B
- 5, available at http://www.epa.gov/otaq/highway
- diesel/regs/ria
- ii.pdf 2 ICCT, May 2009, “Heavy
- Duty Vehicle Market Analysis: Vehicle Characteristics & Fuel Use , Manufacturer Market Shares .”2 unlikely to c ancel each other out. Because we do not have enough data to quantify how these factors affect the emission estimates, we will use the values presented above for purposes of the current anal ys is. On a per
- truck basis, the direct PM exhaust emissions from a certified engine would be 0.01 gram per brake
- horsepower
- hour. As an illustration, we have estimated what that might represent in terms of emissions from a truck operating at 200 horsepower ove r a typical ye ar with 1,200 operating hours . This would be representative of a 500
- hp pumper truck with an average engine operating load of 40 percent of capacit y . This illustration would yield a hy pothetical fire truck that would emit about 5.3 pounds of direct PM exhaust emissions in a year, or 0.002 tons per year, or 0.04 pounds in 8 hours. These estimates are provided as a basis for comparison, as the following sections explore some different scenarios. 

### Estimate of Particulate Matter Emissions from **Emergency Vehicles with Periodic**  **Uncontrolled Emissions** We expect manufacturers who choose to develop optional auxiliary emission control devices (AECD ’ s ) for emergency vehicles to employ

strategies that prevent the occurrence of abnormal conditions with r espect to the emission control sy stem. Where preventive strategies alone are not demonstrated to be failsafe, EPA expects there may be instances where it is justified to provide engine exhaust backpressure relief, either mechanical or through other means. While we expect this will not be a widespread solution, there may be cases where a relief valve may

be employed on a vehicle whose diesel particulate filter ( DPF ) became plugged frequentl y, allowing temporary emission control by

pass to occur as a last re sort to prevent engine failure. We expect manuf acturers would consider reduced PM control as an option of last resort. Nonetheles s, if it were to be employed with DPF’s on vehicles that frequently bec o me plugged , leading to temporary emission control laps es , there would be some potential emissions impacts
. Some factors to consider when estimating potential emission impacts include how many vehicles employ this option, how frequentl y these vehicles are in a condition of reduced PM control, the duration of e ach reduced control event, and the uncontrolled engine
- out PM emission rate. Without speculating what fraction of the fleet may employ this option of last resort, we will focus on a per
- truck estimate for this illustration. Inthis analy sis, we are using a low estimate of engine
- out PM at 0.06 g/bhp
- hr. 3 We are also estimating a high engine
- out PM rate of 0.2 g/bhp
- hr. We chose this as a high
- end value based on the case of a certified engine with a DPF that has a 95 percent removal efficiency
. The engin e - out emission rate would back
calculate to be 0.2 g/bhp
- hr in that case. We do not have specific information about an engine with higher engine
- out PM than this, though it is possible such engines are on the market. We are now going to continu e with our example of a truck with a 500
- hp engine operating at an average load of 40% , for a working power of 200 hp and 1,200 operating hours in a year. If this

3 NREL 2000, DESCE Final Report, test results interpolated for 15 ppm S fuel from results given at 3 and 350 ppm S fuel.3 vehicle has a regeneration interval of 25 engine hours, this example assumes a worst case where the DPF plugs during every regeneration cycle. That is, we assume it is not able to be actively regenerated due to engine operating conditions and reach es a backpressure sufficient to open a by pass every

25 engine hours
. We also estimate the operati ng time under by pass before the plugged DPF is regenerated and normal conditions resume may range from one to four hours. Table 1 presents the results of this illustrative example. **Table 1**  **: Per**  **- Truck**  **Temporary Bypass PM Em ission R**  **ates** Scenario Pounds per Year Tons Per Year Pounds Over Worst 8 H ours 100% Controlled Status 5.3 0.00 3 0.0 4 1
- hour b ypass each cycle at low engine
- out PM 6.3 0.003 0.0 6 1
- hour b ypass each cycle at high engine
- out PM 9.3 0.00 5 0. 1 2 4
- hour b ypass each cycle at low engine
- out PM 9.5 0.00 5 0. 12 4
- hour b ypass each cycle at high engine
- out PM 21.4 0.011 0. 37 As shown in Table 1 , the effects of by pass lead to a quadrupling of annual per
- truck emissions in the case of our high
- end estimate. In the last column, the value presented indicates the 8
- hour period includes a by pass of the length specified with the balance of the time in a controlled status. The final scenario indicates the 8
- hour PM emissions would be less than half a pound if during four of those hours the engine emitted PM at 0.2 g/bhp
- hr. One of the AECD options discussed in the preamble is an engine recalibration. The possibility exists that some manufacturers may choose to employ engine recalibration or alter other engine combustion p arameters to reduce engine
- out PM emissions , reduc ing the soot load to DPF’s . This would work to reduce the occurrence of, or prevent the situation where a DPF could plug and enter into the reduced PM control conditions discussed here. 

### Estimates of Partic **ulate Matter Emissions from Structural Fires**  In the comment letters EPA received urging swift action pro viding relief for emergency vehicles , comparisons were made regarding the magnitude of the pollution from a structural fire in relation to the tailpipe emissions of a fire truck. To provide some perspect ive on this, EPA is providing an example of one possible method of estimating emissions from structural fires, as de scribed in a 2001 report sponsored by EPA as part of its Emission Inventory Improvement Program, with its state regulatory partners . 4

4 Report for the Area Sources Committee of the Emission Inventory Improvement Program (EIIP), Volume III, Chapter 18, Struc ture Fires, January 2001.4 Following the second alternative method for estimating emissions from structural fires described in that report , some national average factors are emplo yed : an average frequency factor of the fires occurring over time in a population , a default fuel loading of tons burned per fire, and an emission factor of PM emitted per ton of fuel burned
. That 2001 document presented a frequency

factor of 2.3 fires per 1,000 residents based on 1994 data. 5 Italso included a PM emission factor of 10.8 lb per ton burned that was derived in 1972 and has been incorporated in both EPA and California methodologies
. 6 Those factors are employed in this anal ys is, along with a 2012 U.S. population estimate of 313 mi llion. 7 The estimate of fuel loading appears to be more variable, thus we present three values here. The 2001 EIIP report estimated a fuel loading of 1.15 tons burned per fire, while an updated CARB area source methodology

guideline estimates fuel loading at 1.28 tons burned per fire. 8 A similar guideline issued by the Bay Area AQMD estimates a fuel loading of 1.95 tons burned per fire
. 9 The methodology

for assessing this value yi elds variable results because it involves assumptions regarding the si ze an d value of a home, its combustible contents, and the percent l oss rate. Using these three different estimates of fuel loadings, EPA has estimated a range of likely emissions from structural fires in the U.S. The results are presented in Table 2. **Table 2**  **: Structural Fire Emission Estimates** Source Pounds PM per fire Tons PM per Year 2001 EIIP 12.4 4,500 1999 CARB 13.8 5,000 1999 BAAQMD 21.1 7,600 From this anal ys is, EPA estimates that something on the order of 4,000 to 8,000 tons of PM may be emitted in the U.S. each ye ar from structural fires , with each individual residential structure fire incident possibly emitting on the order of 10 to 20 pounds of PM. As a comparison, the baseline heav y - dut y fleet at the time of the Heav y - Duty Highway R ule emitted far more direct exhaust PM than is emitted by structural fires in the U.S. Since that time, the PM emissions from the fleet have been substantially reduced; making it likely that the fleet now emits less PM than is emitted by su ch fires. Comparing the estimates from individual fire incidents with the 8
- hour emission estimates of individ ual trucks, even using the high engine
- out PM estimate with 4
- hour by pass, the 8
- hour truck emission s would likely be two order s of magnitude les s polluting than the fire s .

5 Based on total fires reported for 1994 by FEMA with 1994 population data from the US Census Bureau; see EIIP Report at 18.5
- 2. 6 See 2001 EIIP; see also California ARB Area Source Methodology, Structural and Automobile Fires, March 1999, available at http://www.arb.ca.gov/ei/areasrc/ONEHTM/ONE7
- 14.HTM
. 7 Estimate based on U.S. Census Bureau statistics, retrieved May 2012 from http://www.census.gov/ 8 See Note 6 above. 9 Bay Area Air Quality Management District, August 2001, Area Source Methodology, Ac cidental Structural Fires, available at http://www.arb.ca.gov/ei/areasrc/districtmeth/BayArea/C750.pdf
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