Depending on the operating conditions and the age of the converter, mean platinum emissions ranged from 7 to 123 ng m~3 corresponding to emission factors between 9 and 124 ng km~1. There were no statistically signi"cant di!erences between the four converter brands tested. The data from new (12}90 ng km~1) and old catalytic converters (9}26 ng km~1) installed on a medium-powered gasoline engine (1.8 l 66 kW) showed a tendency towards decreasing platinum emission with increasing use. The platinum emissions increased with rising simulated speed and exhaust temperature. The lowest mean emission from new converters (12 ng km~1) was found at a constant speed of 80 km h~1, the highest (90 ng km~1) at 130 km h~1. Using the US72 or the US72-EUDC test cycles the emission factors were higher (37 or 19 ng km~1) than at 80 km h~1 indicating that additional mechanical or thermal impacts enhance the platinum abrasion at cycle conditions. After installing catalytic converters tested with the 1.8 l engine on a smaller engine (1.4 l 44 kW), the platinum emissions measured at the US72 cycle and a high-speed condition (140 km h~1) were only 9 and 22 ng km~1, respectively. Platinum is almost exclusively emitted bound to aluminum oxide particles where (depending on the driving conditions) 43}74% of these emitted particles had aerodynamic diameters '10 lm. The alveolar fraction ((3 lm) was between 11 and 26% (1.8 l engine) and between 21 and 36% (1.4 l engine). If at all, soluble platinum is emitted in only very small quantities ()1%).