The effect of fuel sulfur on NH3 and other emissions from 2000–2001 model year vehicles

Atmospheric ammonia (NH3) is an important precursor to secondary particulate matter formation and information is currently scarce on NH3 emissions from advanced low-emission vehicles using low-sulfur fuels. With the continuing reduction in the level of sulfur in gasoline, it is important to understand how this change could impact NH3 emissions, particularly for advanced vehicle technologies. For this study, a total of 12 California-certified low-emission vehicles were tested with a gasoline containing 5, 30, and 150 ppmw sulfur and with both as-received and bench-aged catalysts. Vehicles were tested on each fuel/catalyst configuration over the federal test procedure (FTP) and US06 test cycles. Both regulated and NH3 emissions were measured in real-time. NH3 emission rates were generally lower than those of other regulated emissions over the FTP and in the range 14–21 mg mi−1 for the fleet. NH3 emission rates were approximately five times higher over the more aggressive US06 cycle compared to the FTP. NH3 emissions were primarily observed during transients, with higher emissions for more aggressive accelerations. Overall, the NH3 emission factors for the newer technology vehicles tested were lower that than those found in previous studies of older vehicle technologies. Sulfur did not affect NH3 emissions over the FTP, but higher NH3 emissions were found for increasing fuel sulfur levels over the US06. Sulfur effects were also observed for nitrogen oxides over the FTP and for all regulated emissions over the US06.