Published in the Proceedings of the
6TH CRC ON-ROAD VEHICLE EMISSIONS WORKSHOP
San Diego, California
March 18-20, 1996

Tom Wenzel
Environmental Energy and Technologies Group
Lawrence Berkeley Laboratory
Berkeley, CA 94720

Marc Ross
Physics Department, University of Michigan
Ann Arbor, MI 48109

Two data sources have become available which allow more thorough characterization of the magnitude and causes of in-use emissions from vehicles with malfunctioning emissions control systems (ECS). Remote sensing (RS) surveys allow the collection of limited emission information on large numbers of vehicles, while "as-received" dynamometer studies allow analysis of detailed emission data on relatively small numbers of vehicles. We examined both types of data to determine the relationship between various vehicle attributes and high in-use emissions in relatively modern (MY87 to 89) cars.

CARB's 1991 remote sensing survey (conducted by the University of Denver) is large enough to calculate the malfunction probability of individual vehicle models, and to examine the relationship between ECS malfunction and technical attributes (such as type of fuel system or transmission) of those models. We found that five models have a probability of ECS malfunction at least 4 times that of all other cars. We have performed several checks (such as limiting the analysis to only those vehicles with multiple remote sensing "hits") that confirm the relationship between vehicle model and malfunction probability. We also examined the effect of RS testing site on malfunction probability and emissions.

We analyzed CARB's dynamometer testing of vehicles in the condition they were received (the Light Duty Vehicle Surveillance Program, or LDVSP, 12) to confirm our findings from the RS data. Our analysis finds the two sources of data quite consistent; vehicle models identified as having a high malfunction probability in the RS data dominate the malfunctioning vehicles in the LDVSP (as well as three other sets of dynamometer data). This result suggests changes in the current policies to reduce in-use emissions.

The LDVSP data provide accurate information on HC and NOx emissions as well as CO emissions. Comparison of the three pollutant emissions, under different driving conditions, may help in developing separate emission parameters for specific ECS failure modes. These failure mode-specific parameters can then be coupled with surveys of ECS failure modes (EPA's Tampering Surveys) to develop an inventory of emissions from ECS malfunction.

The understanding of emissions from vehicles with malfunctioning emissions control systems (ECS) has, to date, been rudimentary. While there has been some data on high-emitters of CO, the quantity of malfunction emissions of HC and NOx has primarily been estimated as the difference between estimates of total automotive emissions and measurements and estimates of other sources. In addition, the assumed structure of the malfunction emissions, such as their dependence on vehicle age and cause of malfunction, has essentially been based on vehicles with old ECS technologies and carburetors, in use when leaded gasoline was available. Part of the lack of information is due to the design of much of the "in-use" testing: Recruitment of vehicles depends on the voluntary participation of owners, and vehicles have often been screened to omit those which have something wrong that might be regarded as owner responsibility, such as a disconnected hose. While this may be appropriate for legal purposes it has made understanding of malfunction emissions difficult.

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