Emissions reduction benefits and cost-effectiveness of catalytic converter replacement for light-duty vehicles in the South Coast Air Basin

The older Light-duty vehicles (LDV) form a small segment of the on-road vehicle population in the South Coast Air Basin (SoCAB), however, contribute a significant portion of the ROG and NOx emissions. This study investigated emissions reduction benefits of replacing the oxygen (O2) sensor and catalytic converter ("catalyst") for older vehicles lacking an OBD system. Malfunctioning components such as the catalyst and O2 sensor increase vehicle's excess emissions, and can be easily replaced. Study vehicles underwent a Smog Check and FTP test at baseline and after component replacements and after adding mileage. A pre-pilot feasibility study conducted to investigate range of emissions benefits from these replacements showed relatively low benefits from the O2 sensor replacements compared to the catalyst replacements. A follow-up larger pilot study continued with O2 sensor and catalyst replacements and found similar results. Correlations of the ROG + NOx emissions benefits data with baseline ASM data indicated that high-emitter vehicles with ASM NOx above 400 ppm had higher emissions benefits from the O2 sensor replacement.; During this study three types of catalysts were compared for their conversion efficiency: older aftermarket catalyst, the OEM catalyst, and the newer OBDII complaint aftermarket ("OBDII catalyst"). The testing was done for "green" catalyst i.e. with zero to fifty miles, and "aged" catalyst where vehicles were recaptured after adding minimum 6000 miles. Results showed OBDII catalyst were comparable to the OEM catalyst, although costs were atleast 50% lower than average cost of OEM catalysts. The older aftermarket catalyst performance was inferior compared to the OEM catalyst when "green", and follow-up retesting of vehicles after adding mileage indicated emissions increased by more than 100% compared to baseline. Vehicles with OEM and OBDII catalyst replacements when recaptured after mileage increase, retained approximately 30% of the emissions benefits.; A cost-effectiveness estimate was done for OBDII catalyst replacement assuming implementation starting in 2008 and catalyst replacements done for the 1980-1995 light-duty vehicles. The cost-effectiveness on a per year basis is estimated to be approximately {dollar}24,000-{dollar}34,000 per ton of ROG+NOx decrease.