Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001) / Chapter Skim
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5 Estimating Inspection and Maintenance Emissions Reductions Using the Mobile Model
5 Estimating Inspection and Maintenance Emissions Reductions Using the Mobile Model
Pages 118-145
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From page 118... ...
USE OF MOBILE IN REGULATORY APPLICATIONS The Clean Air Act and its amendments require that areas that have not met the National Ambient Air Quality Standards (NAAQS) develop state implementation plans (SIPs)
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From page 119... ...
During a conformity lapse, projects that are already under construction can proceed, but new projects requiring federal funding or approval cannot be advanced until the conformity lapse has been remedied. For both of these applications, states and regions outside California use EPA's MOBILE emissions factor mode} for estimating emissions and emissions reductions from mobile-source control programs such as I/M (California has its own emissions factor model, EMFAC)
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From page 120... ...
On the other hand, if states claim too much credit for I/M and the emissions reductions are not fully realized, then progress toward attaining clean air standards is hindered. It should be noted that MOBILE estimates emissions factors in grams per mile by vehicle class (e.g., passenger cars, light-duty trucks, and heavy-duty diesels)
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From page 121... ...
There have been only a few comparisons of emissions reductions estimated from program data or remote-sensing measurements to MOBILES predictions. These comparisons are shown in Table 5-2 for several I/M programs across the counky; evaluations for most ofthe I/M programs listed in the table were discussed in Chapter 3.
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From page 122... ...
. With these Tower emissions rates for future years in MOBlI-E6, as shown in Figure 5-l, the I/M credits are likely to be lower in MOBILES than in MOBILES.
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From page 123... ...
85 46 100 83 43 90 89 46 83 86-103 76-93 76-84 3-6 105-121 21 Cars, 209 Trucks, 72 14 aBoth program and MOBILES estimates are fleet average grams per mile emissions. Colorado audit estimated an 8% reduction in CO emissions for the IM240 program, compared with ~ 7°/O for the Serious Area CO Mode!
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From page 124... ...
fleet characterization inputs. The model estimates emissions credits for the effects of up to five I/M programs specified by the user.
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From page 125... ...
. · Vehicle classes covered (LDGV, light-duty gasoline truck (I DGT)
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From page 126... ...
This definition includes only one ofthe four types of noncomplying vehicles shown in Figure 5-2, and in the past, states have tended to estimate the compliance rate as the proportion of registered vehicles that actually take an I/M test and thus underestimate the true noncompliance rate and overstate the I/M benefits. In MOBlLE5, there is no default value for the compliance rate; it must be specified in the input file.
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From page 127... ...
Similarly, MOBlLE6 defines noncomplying vehicles as "vehicles which show up for the initial test, but drop out of the process prior to a successful passing result or a waiver" (EPA 1 999e)
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From page 128... ...
Waiver Rate Waiver rate refers to the fraction of vehicles that fail their initial tests but were never fully repairedbecause the repair cost limit (or some other criterion) has been met; these vehicles have complied with the program requirements but are still failing vehicles.
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From page 129... ...
For example, MOBILE has emissions rates rising over time as vehicles age and the emissions-control system deteriorates, but some ofthe fixed parameters (e.g., failure rates on these oldervehicles and age distribution of the fleet) stay constant.
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From page 130... ...
The same FTP databases that were used to determine fleet average emiss~ons were also used to determine emissions rates for normal and high emitters (by vehicle class, model-year group, and technology type)
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From page 131... ...
However, because the fleet average emissions rates are adjusted using the Dayton IM240 data, the Dayton data are thus used to determine the fraction (but not the absolute levels) of high and normal emitters.
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From page 132... ...
year 1981 and 1982 vehicles and is plotted on a logarithmic scale to reduce data scatter. Data from Roadside Testing Exhaust emissions test data cart also be obtained Dom vehicles subject to roadside tests.
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From page 133... ...
TIM Credits The I/M credits are applied to the fraction of the fleet that is identified and repaired from emissions levels considered to be of high-emitter status due to either malfunctioning of, or tampering with, the emissions-controT systems. The credit for I/M programs depends on several factors, including the identification rate, waiver rate, and after-repair emissions rates.
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From page 134... ...
20% (D 3 1 5% ~ 10% 0% 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 18O,000 200,000 Accumulated mileage FIGURE 5-4 Basic emissions rates of HC that have not been adjusted for I/M. Average emissions rates, normal- and high-emitter emissions rates, and the estimated fraction of high emitters in the fleet are shown.
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From page 135... ...
Note that the change in emissions as a function of mileage for the repaired vehicles is not the deterioration rate for the repaired vehicles; rather, these emissions rates are used to determine the I/M credit at a given age. Note also for this example that the EPA methodology results in the repaired vehicle emissions multiple ofthe normal emissions rate increasing from 0 to about ~ 00,000 miles and then decreasing until the repaired and normalemitter rates are the same at about 170,000 miles.
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From page 136... ...
The high emitters, therefore, consist ofthree types of vehicles: (~) the identified high emitters that are repaired (but with emissions rates higher than normal emitters)
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From page 137... ...
Emissions before I/M are the basic emissions rates described previously, and average emissions after I/M are calculated as the weighted average across subsets of vehicles as shown in Table 5-3.
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From page 138... ...
FH X FID X FNC FH X FID X FW FH X FID X FR .—N EH EH * 0.80 ER Note: The average for each vehicle-class, model-year, technology group is the weighted average emissions rate across five subsets of vehicles.
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From page 139... ...
Although no analyses have been published that indicate significantly greater emissions reductions for annual programs, if repair durability is less than 2 years, annual programs are likely to reduce emissions more than only a few percent from biennial programs. When MOBlLE6 is released, the additional credit modeled for annual programs should be compared with real-worId data.
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From page 140... ...
Some of these repairs will not be done or not be long-lasting, and the vehicle will revert back to high-emitter status just after the test. OBD Effects MOBlLE6 includes emissions reductions for vehicles equipped with OBDIT systems ( 1996 model years and later)
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From page 141... ...
Figure 5-7 (EPA 1999f) shows MOBlLE6 projected nonmethane HC basic emissions rates for light-duty Tier ~ vehicles with OBD systems from EPA's draft MoBlLE6 documentation (EPA ~ 999i)
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From page 142... ...
10.0 12.5 No OBO J No IM — —OBO / No IM - - - OBO I IM ] ~.0 17,5 20.0 FIGURE 5-7 MOBILE6 non-methane HC basic emissions rates for light-duty Tier 1 vehicles with OBD systems.
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From page 143... ...
The Clean Air Act allows California to regulate automobiles in the state and use its own computer models to predict emissions inventories. The California Air Resources Board (CARB)
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From page 144... ...
Like MOBILE, EMFAC has overpredicted emissions reductions from the state's I/M programs, thus generating SIP credits that were too large and contributing to problems in meeting air-quality standards. With EMFAC7G (the version prior to EMFAC2000)
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From page 145... ...
There are also a large number of assumptions internal to the model that significantly affectMOBlLE's emissions projections and I/M credits. These include the absolute number and average emissions of high emitters, average emissions of initially failing end passing vehicles, average repair effects, identibcation rates under different cutpoints, and OBD effects.
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