Effects of Ultra-Low Sulfur Gasoline on Emission from Tier 2 Vehicles in the In-Use Fleet. Final Report

摘要

Fuel sulfur content has long been understood to affect the performance of emission aftertreatment catalysts in light duty vehicles, where the sulfur and its oxides occupy active precious metal sites and oxygen storage materials, reducing the catalysts efficiency in destroying pollutants. Numerous studies have shown the direct impact of fuel sulfur levels above 30 ppm on emissions, data that formed the basis of the sulfur controls in EPA's Tier 2 rulemaking for light duty vehicle emissions, published in 2000. Following the successful implementation of the Tier 2 sulfur standards, new research has focused on the emission reduction potential of lowering sulfur levels below 30 ppm, particularly on Tier 2 and newer technology vehicles, under the hypothesis that increased reliance on the catalytic convertor will result in a higher sensitivity to fuel sulfur content. A 2005 study conducted jointly by EPA and several automakers found large decreases in NOx and HC emissions from vehicles meeting Tier 2 Bin 5 emission levels when operating on 6 ppm versus 32 ppm sulfur test fuel. In order to gain further understanding of how these emission reductions would translate into the in-use fleet, EPA conducted the study described here to assess the state of sulfur loading (poisoning) in typical in-use vehicles, as well as the effect of fuel sulfur level on these vehicles during subsequent mileage accumulation.