There are 2 general uses for remote sensing: Enforcement and Monitoring. There are two enforcement applications: Clean Screening (CS) and Gross Emitter Identification (GEI). The Monitoring application is generally referred to as I/M Program Evaluation (PE). Applied together, the three represent the most powerful supplement to traditional inspection and maintenance programs.
The USEPA formally recognized (and approved) each remote sensing application application through the issuance of guidance documents. Today, states are free to incorporate remote sensing as a supplemental enforcement tool in I/M programs and may consult either the General RSD Guidance (“the GEI guidance”) or the CS Guidance when designing their programs and quantifying the air quality impact of the remote sensing supplementI. The impact is quantified by modeling the emissions generated by the I/M program. MOBILE5a is the model currently used by states to quantify the benefit of their I/M programII. Guidance credit utilities contain the algorithms that drive the models and define the emissions reductions (commonly known as “credits”) gained or lost by either remote sensing GEI or CS, respectively.
The USEPA has also recognized PE as the third, and potentially most powerful, application of remote sensing. The PE draft guidance is currently being reviewed by government and industry stakeholders and is scheduled for release in late 2002.
This section presents remote sensing’s legislative history and reviews key studies and reports that lead to the widespread acceptance of all three remote sensing applications by the USEPA and state agencies.
The figure below is an evolutionary timeline of US remote sensing legislation overlaid with ESP’s AccuScan technology milestones.
Dr. Donald Stedman of the University of Denver is credited with inventing remote sensing. He built his prototype CO only device in 1987 under a USEPA grant. The concept of on-road emissions measurement was received with great skepticism by some and great enthusiasm by others.
The supporters were pitching RSD as the silver bullet that would replace I/M and save all of us from this necessary evil. The early skeptics, among them the USEPA, set out to prove it could not replace the I/M program it had develop and implemented over the 1980s. Glover and Clemmens (91) compared RSD results to IM240 resultsIII. Despite the lack of speed and acceleration data, Glover concluded RSD could identify a portion of the gross emitters, and touted its monitoring value. In his subsequent study, Whitney and Glover (1992) established definitively that RSD cannot replace I/M, but would serve as a fine supplement. IV
Among the early supporters of RSD was Texas Rep. Joe Barton. He lobbied to have a small, but critical, reference to remote sensing included in the Clean Air Act Amendments of 1990. The USEPA promulgated rules covering on-road testing in November 1992. EPA backed supplemental use of RSD from the beginning (early 90s), but grew tired of the “replacement” rhetoric. Phil Lorang (the individual responsible for drafting the 1992 0.5% rule and the 98 guidance document) wrote in an October 6, 1993 memo to Jay Messer, Acting Director of the USEPA’s Atmospheric Research and Exposure Assessment Laboratory; “On-road testing, such as RSD, is required as a supplement on a (for now) small fraction of vehicles (at least 0.5%). RSD cannot, however, replace the high-tech I/M test with equal benefit as one could infer from the press release. We imposed the RSD requirement in faithfulness to the CAA, but over the opposition of states, which viewed it as an extra burden and a technical uncertainty. Despite our support for RSD as a supplement to I/M, we are perceived by some to be biased against it because we do not agree that it can and should replace other motor vehicle I/M programs.”
All “enhanced” areas are required by the Clean Air Act Amendments to supplement their Enhanced I/M programs with an on-road/remote sensing element. The Clean Air Act Amendments require that a minimum of 0.5% of the eligible motor vehicle population in the I/M area be tested annually.
Section 51.371 of the Code of Federal Regulation (CFR) covering Enhanced I/M programs defines on-road testing as the measurement of HC, CO, NOx and/or CO2 emissions on any road or roadside in the non-attainment area or the I/M program area. On road testing is required in enhanced I/M areas and is an option for basic I/M areas.
The general requirements specified in CFR 51.371 are:
1. On-road testing is to be part of the emission testing system, but is to be a complement to testing otherwise required.
2. On-road testing is not required in every season or on every vehicle but shall evaluate the emission performance of 0.5% of the subject fleet, including any vehicles that may be subject to the follow-up inspection provisions of paragraph 4) below, each inspection cycle.
3. The on-road testing program shall provide information about the emission performance of in-use vehicles by measuring on-road emissions through the use of remote sensing devices or roadside pullovers including tailpipe emission testing. The program shall collect, analyze and report on-road sensing data.
4. Owners of vehicles that have previously been through the normal periodic inspection and passed final retest and found to be high emitters shall be notified that the vehicles are required to pass and out-of-cycle follow-up inspection; notification may be by mailing in the case of remote sensing on-road testing or through immediate notification if roadside pullovers are used.
Despite the legislative mandate, states managed to avoid the testing because of controversy surrounding the overall “enhanced” testing requirements, particularly centralized IM240 testing. States wanted flexibility to choose the I/M test and the I/M program design. The USEPA questioned the equivalence of others approaches. The California EPA and the USEPA agreed to study the matter in 1994. It was not until a 1995 California Air Resources Board (CARB) study determined the relative benefits of IM240 vs. ASM and the USEPA granted states flexibility to choose their I/M program test and design that the USEPA began enforcing the 0.5% RSD rule.
ESP performs eight 0.5% studies annually in the enhanced areas of CT, NY, MD, VA, IN, IL, PA, and CO.
The 1992 USEPA rule established the precedent for high emitter identification with language calling for out-of-cycle follow-up inspection. However, states interested in supplementing their programs with GEI had no basis for estimating the additional credit they would receive for implementing GEI. The community lacked guidance. The 1992 USEPA evaluation was accompanied by other independent industry studies that produced favorable conclusions. Among them was an April 1996 study by the Desert Research Institute that concluded that a GEI could reduce Orange County CO and HC emissions by 46 and 36 percent at a cost of $9 per vehicle. The I/M community was beginning to recognize the air quality benefits of remote sensing based GEI, and the USEPA came under increasing pressure to formalize guidance and a credit utility.
In September 1996, the EPA’s Office of Mobile Sources (Phil Lorang’s group) issued the “User Guide and Description for Interim Remote Sensing Program Credit Utility” which provides some credits for RSD programs. In the User guide, EPA-OMS admits it “faced a tradeoff between when its first formal guidance on RSD credits would be released and how comprehensive and representative those credits could be. The choice EPA has made is to provide its credits sooner than later, realizing that they may not be as large as they could be with more investment in time, and may not cover every case of interest to users. One tradeoff has been the availability of relevant data; EPA has chosen to make use of data collected up to and including the 1994-95 El Monte study; and not wait to receive and analyze data collected in Arizona or elsewhere in 1996 and 1997. The data from the Arizona RSD program will indeed be valuable in helping determine what RSD credits could be.” V
Colorado was one of the first states to comply with the 0.5% RSD testing requirement and had amassed a sizeable dataset by the time the 1998 GEI guidance was issued. Although Colorado was an “enhanced” I/M area, its air quality had improved substantially since it began testing motor vehicles and was looking for ways to lessen the burden of the I/M program on Colorado motorists.
Examination of its RSD dataset revealed that its cleanest on-road vehicles could be conveniently and effectively identified as “clean” without the need for a burdensome station-based test. Encouraged by the comparison of its 0.5% RSD data to previous and subsequent IM240 results on the same vehicle, Colorado elected to commission a more definitive clean screen evaluation in its northern city of Greeley. ESP’s predecessor company (RSTi) had provided the 0.5% data and was chosen to perform the Greeley study. The Greeley results showed low false passes and demonstrated that RSD was an effectively tool for clean screening. ESP prepared a formal report to the USEPA. Based on the Greeley data, the USEPA’s FACA Committee recommended a credit scheme that included clean screening up to 50% of the fleet with minimal loss of excess repairable emissionsVI. The Clean Screen guidance document was issued in late1998.
Figure 1: Slides from Clean Screening I/M Credits Presentation at 5/19/98 FACA Meeting
Congress’s Clean Air Act (CAA) Amendments and the USEPA’s I/M rule require biennial program effectiveness evaluation (a quantification of the mobile source emissions reduced by the I/M program).VII
In January 1998, EPA revised the I/M rule's original provisions for program evaluation by removing the requirement that the evaluation be based on IM240 or some equivalent, mass-emission transient test (METT) and replacing this with the more flexible requirement that the program evaluation methodology simply be "sound"VIII. In October 1998, EPA published a guidance memorandum that outlined what the Agency considered to be acceptable, "sound," alternative program evaluation methodsIX . All the methods approved in the October 1998 guidance were based on tailpipe testing and required comparison to Arizona's enhanced I/M program as a benchmark using a methodology developed by Sierra Research under contract to EPA. Even though EPA recognized that an RSD-based program evaluation method might be possible, a court-ordered deadline of October 30, 1998 for release of the guidance prevented EPA from approving an RSD-based approach at that time. EPA420-S-98-015, October 1998, Inspection and Maintenance Program Effectiveness Methodologies identifies four methods for program evaluation: The Sierra Research Method, The NYTEST (VMAS) Method, The RG240 Method, and the RSD fleet characterization method. It approves the first three while reserving judgment on RSD, which required further study. The most powerful use of remote sensing has unfortunately been the most neglected.
Today, the USEPA’s Dr. Jim Lindner, with the help of other government and industry stakeholders, has drafted a guidance document that recognizes the value of remote sensing program evaluation and identifies three RSD-based PE techniques. It is currently under review and comment is expected to be released in late 2002. The guidance recommends three methods (the Step Change, the Comprehensive, and the Reference Methods) for RSD-based program evaluation and considers the combination of RSD and one of the original three as the best evaluation tool going forward.
The Step Change and Comprehensive evaluation methods are quite similar. Remote sensing measurements are made on a fleet of vehicles in an I/M area. The fleet is then divided into two sub-fleets, based on whether or not individual vehicles have been tested under the current I/M program. The emissions of the two sub-fleets are then compared, after accounting for differences in vehicle type and age. The difference in the emissions of the tested fleet and the untested fleet is the apparent benefit of the I/M program in reducing emissions.
The Reference Method is designed to measure the full effect of an I/M program on a vehicle fleet, by comparing the emissions of a fleet subject to I/M with the emissions of a fleet not subject to I/M.
The USEPA considers the combination of remote sensing and I/M data to be the most effective tool for program effectiveness evaluation, a sentiment echoed by the National Research Council’s Committee on Emissions Inspection and Maintenance Programs.X
II There are a number of routes by which to obtain further and more detailed information about the MOBILE model. The best of these is the Modeling page within the Office of Mobile Sources Web site: www.epa.gov/omswww/models.htm A User’s Guide to MOBILE5a and MOBILE6 (currently under development are available there.
III Identifying Excess Emitters with a Remote Sensing Device: A Preliminary Analysis; Glover, Edward L. and William B. Clemmens, SAE Paper 911672 1991.
IV Evaluation of the Ability of Multiple Remote Sensing Devices to Identify High Emitters; Whitney, Kevin A. and Glover, Edward L., SAE Paper 922315, 1992.
VI The Denver 0.5% report, the Greeley Clean Screen report, and the FACA Committee report are available on the USEPA website: http://www.epa.gov/oms/rsd.htm
VII Section 182(c)(3)(C) of the CAA requires that all states subject to enhanced I/M biennially prepare a report to the Administrator which assesses the emissions reductions achieved by the program.
X Holmes, K. John, NRC Senior Staff Officer; Evaluating Vehicle Inspection and Maintenance Programs; National Research Council’s Committee on Vehicle Emissions Inspection and Maintenance Programs; Presentation at the 2001 Clean Air Conference, Estes Park, Colorado; September 12th, 2001 http://www.ncvecs.colostate.edu/cac.docs/cac18.docs/CAC17PrelimAgenda.htm
