Regulations and Fuel Standards
Currently, EPA’s Tier 2 light-duty emissions regulation, finalized in December 1999, requires U.S. gasoline suppliers to meet a 30 ppm average sulfur level with a maximum refinery gate cap of 80 ppm and a 95 ppm retail sulfur cap. This requirement took effect in 2006. California’s gasoline sulfur cap, as required by ARB’s Low Emission Vehicle II (LEV II) program, reduced the gasoline sulfur cap from 60 ppm to 30 ppm in 2006 and that sulfur cap was further reduced to 20 ppm in 2012 for gasoline sold in California.
The state of California recognized the benefit of reducing sulfur in gasoline on the emission control of existing vehicles and the need for low sulfur fuel to optimize the performance of new vehicles designed to meet their stringent LEV II vehicle standards. As a result, California, in establishing its Phase II reformulated gasoline requirements, set an average sulfur level of 30 ppm, with a cap of 80 ppm sulfur in gasoline. In 2006, ARB further reduced the sulfur level to a cap of 20 ppm. Current gasoline sulfur levels in California average a bit below 10 ppm. For similar reasons, the European Union (EU) agreed to establish a two phase reduction in gasoline sulfur to <150 ppm in 2000 and <50 ppm in 2005. The EU further reduced its fuel sulfur levels to maximum of 10 ppm starting in 2009. Similarly, starting in April 2005, Japan reduced its fuel sulfur level to a maximum of 10 ppm for gasoline and diesel fuels, and South Korea has also reduced its gasoline sulfur limit to 10 ppm starting in 2009. China has recently committed to reducing its gasoline sulfur level to 10 ppm maximum by December 31, 2017.
In March 2013, EPA proposed its Tier 3 Motor Vehicle Emission and Fuel Standards, which includes creation of a national set of criteria pollutant standards largely harmonized with California’s LEV III emission standards, and proposed reduction in gasoline sulfur levels from the current 30 ppm average to a 10 ppm average across the nation starting in 2017. According to EPA, the feasibility of the proposed Tier 3 30 mg/mi NMOG+NOx 2025 fleet average exhaust emission standard depends on a degree of emissions control from exhaust catalyst systems that will require gasoline at 10 ppm sulfur or lower. The most likely control strategies would involve using exhaust catalyst technologies and powertrain calibration primarily focused on reducing cold-start emissions of NMOG and on reducing both cold-start and warmed-up emissions of NOx.
EPA notes that the impact of gasoline sulfur poisoning on exhaust catalyst performance and the relative stringency of the Tier 3 standards, particularly for larger vehicles and trucks, when considered together, make a compelling argument for the virtual elimination of sulfur from gasoline. While lowering gasoline sulfur to levels below 10 ppm would further help ensure in- use vehicle compliance with Tier 3 standards, EPA believes that a gasoline sulfur standard of 10 ppm would allow compliance by gasoline-fueled engines with a 2025 national fleet average of 30 mg/mi NMOG+NOx.
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