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FTP-UDDS (urban dynamometer driving schedule) exhaust particulate matter (PM) emission rates were determined for 361 light-duty gasoline (LDGV) and 49 diesel passenger vehicles ranging in model year (MY) from 1965 to 1997. LDGVs were recruited into four MY categories. In addition, special effort was made to recruit LDGVs with visible smoke emissions, since these vehicles may be significant contributors to the mobile source PM emission inventory. Both light and heavy-duty diesels where included in the passenger diesel test fleet, which was insufficient in size to separate into the same MY categories as the LDGVs. Vehicles were tested as-received in three areas: Denver, Colorado; San Antonio, Texas; and the South Coast Air Quality Management District, California. The average PM emission rates were 3.3, 79.9, 384 and 558 mg/mi for 1991-97 MY LDGVs, pre-1981 LDGVs, smoking LDGVs and the diesel vehicles, respectively.

In the USA, hydrogen sulfide emissions from three-way catalytic converter-equipped automobiles are effectively suppressed by the addition of nickel to catalyst formulations. This approach is generally not utilized in catalyst formulations for Europe because of European concern about the health, safety and environmental issues surrounding the use of nickel. A modified form of iron oxide has been identified which suppresses hydrogen sulfide emissions from three-way catalysts. This suppression has been achieved without affecting the fresh or aged performance of the catalyst, a problem often encountered with other materials. The performance and durability of catalyst formulations incorporating the new material are demonstrated with a variety of aging and evaluation protocols.

The emphasis on H2S emissions has increased in recent years due to significant levels being emitted by some single-bed three-way catalyst equipped vehicles. Studies to identify the mechanisms of H2S formation have suffered due to the sample time dependent wet chemical methods used for H2S analyses. A simple but effective dilution and sample system has been developed for use with a commercially available gold film H2S analyzer. This provides semi-continuous H2S analyses directly from the engine exhaust and has proven to be an excellent tool for defining the effects of vehicle operating conditions on H2S formation. Engine dynamometer studies have been used to investigate the effects of air/fuel, catalyst inlet temperature, and transient duration on sulfur storage and release over single-bed three-way catalyst systems.

Recent reports of significant H2S emissions from single-bed three-way catalyst equipped vehicles have prompted vehicle and laboratory studies of the mechanism of H2S formation over three-way catalysts. Vehicle studies have shown the occurrence of short duration H2S emissions significantly higher than fuel sulfur inlet levels under certain transient conditions. These emissions cannot be explained by the previously reported steady-state conversion of SO2 to H2S. Laboratory flow reactor studies have identified a second mechanism for H2S formation involving the rapid reductive release of sulfur stored on the catalyst surface. This mechanism can account for H2S emission levels which can significantly exceed inlet fuel sulfur levels for short durations. Results are presented to define factors which affect H2S formation under these two mechanisms and to determine methods for controlling these emissions under vehicle operation.

The sulfur dioxide to sulfur trioxide conversion has been measured for three different automotive exhaust catalysts. Two of the catalysts were 1975 production catalysts (Engelhard IIB and Matthey-Bishop 3C) and the third is a palladium catalyst on a monolith support. The carbon monoxide and propylene conversions were also measured so that the activity of the three catalysts for these gases could be compared to their sulfur dioxide activity. The measurements were made using a flow reactor with simulated exhaust gas and show that, while the carbon monoxide and propylene conversions were very similar for all three catalysts, there was a wide range of sulfur dioxide conversions. At 525°C and 73,000 hr-1 space velocity the sulfur dioxide conversion was 70% for the Engelhard IIB, 40% for the Matthey-Bishop 3C and from 25 to 70% for the palladium catalyst. The palladium catalyst has a range of conversions under these conditions which are associated with different states of the catalyst.