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Implications of Using MVEI 7f and MVEI 7g for Carbon Monoxide (CO) Conformity Determination


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Suggested Citation:
Leeman, Whitney R. and Tom P. Kear (1997) Implications of Using MVEI 7f and MVEI 7g for Carbon Monoxide (CO) Conformity Determination. Institute of Transportation Studies, University of California, Davis, Presentation Series UCD-ITS-RP-97-06

Presented at the Air & Waste Management Association's 90th Annual Meeting & Exhibition

The California Air Resources Board (CARB) developed updated versions of their motor vehicle emissions inventory (MVEI) models to more accurately predict impacts on air quality due to motor vehicle emissions. CARB submits MVEIs to the Environmental Protection Agency (EPA) with the state implementation plan (SIP), to support air quality attainment or maintenance plans and to set emission budgets for all counties within the state of California. Air quality attainment or maintenance plans are designed to achieve and maintain primary and secondary air quality standards promulgated under the Clean Air Act (CAA). Motor vehicle emission budgets, or allowable emissions of pollutants from motor vehicles, are determined using MVEI models. As MVEI models improve, budgets in the attainment or maintenance plans set with older models must still be met unless the SIP is revised.

Metropolitan Planning Organizations and the U.S. Department of Transportation must demonstrate that proposed transportation plans and programs are consistent with the SIP by showing that emissions associated with these plans and programs do not exceed emission budgets. Further, a specific project cannot create new or worsen existing "hot spots". This requirement is known as "conformity". To comply with the conformity requirement, the California Department of Transportation (CALTRANS) uses CARB's MVEI models to estimate emissions from proposed projects, even though the models were not developed or intended for this purpose.

The changes made to CARB's MVEI models have significant impacts on modeled emissions of carbon monoxide (CO). The purpose of this paper is to describe changes made to MVEI 7f that significantly impact prediction of modeled CO emission rates and total CO emissions. Using the South Coast Air Basin (SCAB) as an example of a CO non attainment area, MVEI programs were run for several calendar years to compare MVEI 7f CO emission rates and inventories for the SCAB with those predicted by MVEI 7g. The accuracy of CARB's MVEI models in terms of "real world" emissions is not addressed in this paper, rather, a description of the changes made to the MVEI models (particularly EMFAC) is given and the consequences of using the MVEI models for conformity is explored.