For many pollution control devices, the target removal efficiencies are specified as percentages. For catalytic converters in vehicles, however, the target removal efficiencies are either discussed in rather vague terms, such as "guaranteed performances" for 10 years or 100,000 miles, or are specified in grams/mile.
The g/mile specifications are based on standardized tests such as the EPA's FTP75 (see SAE Handbook, Section 13) and depend on vehicle class, weight and year of manufacture.
Perhaps the most authoritative source of information on these air pollutant emission factors for vehicles (analogous to those summarized for stationary emission sources in Table 4.2 of de Nevers, op. cit.) can be found at
http://www.epa.gov/oms/ap42.htm.
Here is an illustrative calculation for CO emissions.
Assume that the CO output from an automobile engine is 380 grams per gallon of gasoline before the exhaust gases enter the catalytic converter. Express this number as (a) % incomplete combustion and (b) CO emissions in g/mile.
(c) Determine the efficiency of the catalytic converter (in %) if the standard for this vehicle class is 2.10 g/km.
Make the (reasonable?) assumptions that gasoline can be represented as CH1.85, that its density is 0.7 g/cm3 and that the efficiency of the engine is 20 miles/gallon.
Answers: (a) ~7.1% (reasonable?); (b) 19 g/mile; (c) 82%.
lrr3@psu.edu (revised 10/18/98)