Platinum Group Elements in the Environment: Emissions and Exposure - Reviews of Environmental Contamination and Toxicology - page 116

The distribution size of particles emitted from the converter (carrier material) is
independent of the wear of the device.
The PGE emission rate and emission proportions among Pt/Pd/Rh depend on the
following parameters (Artelt et al. 1999b; Whiteley and Murray 2003; Hoppstock
and Sures 2004): speed of the vehicle, driving style (erratic stop-start flows),
engine type, type and age of the catalytic converter, and nature of additives used in
the fuel. Emissions may increase because of poor engine performance, for example,
erratic fuel ignition or excessively hot exhaust fumes, which can damage the cata-
lytic converter.
In practice, either direct or indirect approaches are used to determine the amount
of PGEs emitted from a VEC (Palacios et al. 2000b; Moldovan et al. 1999).
The indirect technique consists of determining traffic-related PGE emissions in
various environmental compartments, and comparing the obtained results with
traffic volume data for vehicles equipped with catalysts (Helmers and Mergel 1998;
Leœniewska et al. 2001). In the direct method, samples of exhaust fumes are
collected that appropriately represent released particle levels. Sampling can be
conducted under laboratory conditions by employing a computer-operated
dynamometer. Dynamometric experiments, aimed at direct measurement of Pt from
three-way catalysts, were performed on various engines and catalysts (Artelt et al.
1999b). The following parameters were considered while performing these
experiments: manufacturer of the catalyst, catalyst wear, cubic engine capacity
(displacement), and vehicle speed. The results (Artelt et al. 1999b) give rise to the
following conclusions:
• Pt concentrations in exhaust fumes range from 7 to 123 ng m −3 , which is equiva-
lent to the emission coefficient of 9-124 ng Pt km −1 .
• Similar emission levels were observed in catalytic converters of different designs
and manufactured by various producers.
• The amount of released Pt increases with rising simulated speed, reaching values
above 90 ng km −1 at 130 km hr −1 (for a new converter), and exhaust temperature.
• A three-way catalytic converter, in a car with a 1.4 L engine, shows a fourfold
decrease in emitted Pt when compared to a car with a 1.8 L engine.
• No significant differences in the amount of released Pt were found when three-
way catalytic converters (at various stages of wear) were compared at a speed of
80 km hr −1 .
• The amount of released Pt decreases with increasing catalytic converter wear;
this phenomenon was observed at higher velocities.
• Pt emissions were higher in city driving, when compared to driving with a mean
speed of ~80 km hr −1 , despite the fact that city driving is characterized as having
lower velocity and lower exhaust fume temperature.
A similar experiment was performed by Moldovan et al. (1999). The results also
demonstrated that PGEs are released at ng km −1 levels. Moreover, significant
amounts of Pd and Rh were found in a diesel catalyst labeled as Pt only. Similarly,
Pd and Rh were also found in exhaust fumes from these catalysts.