Impacts of motor vehicle inspection and maintenance on emission reductions in Southern California

The effectiveness of a proposed California mandatory annual vehicle inspection/ maintenance (I/M) program in reducing reactive hydrocarbon (RHC) and oxides of nitrogen (NO x ) emissions is evaluated in this report. Emission factors are derived from California in-use light duty passenger vehicle data by simple linear regression analysis for pre- and post-maintenance conditions. Percentage reductions in emissions are calculated, based on assumed vehicle fleet mixes, and compared with estimates from the California Air Resources Board (CARB) and the California South Coast Air Basin Air Quality Management Plan (AQMP). Future year estimates of RHC and NO x emissions predict smaller RHC reduction than the CARB in both 1982 and 1987. NO x reduction is underpredicted by the CARB in 1987. A comparison of reductions determined in this study with the South Coast Air Basin AQMP shows that the RHC reductions expected are equivalent; the AQMP NO x reduction is significantly lower. These results have significance in meeting future air quality goals for Southern California, and point out the effectiveness of an I/M program in reducing total RHC and NO x emissions from light duty passenger vehicles.