Vehicle Emissions Reduction

Another important reason to eliminate lead in gasoline is to allow the use of catalyst technology to reduce CO, HC and NOx emissions from vehicles.

The impact of leaded gasoline on catalyst performance was studied by the US EPA in 1984. Twenty-nine in-use automobiles with three-way catalyst emission control systems were misfueled with leaded gasoline in order to quantify the emissions effects. The vehicles used between four and twelve tanks of leaded gasoline with an average lead content of 1.0 grams Pb per gallon. Four different test programs were conducted with different misfueling intensities (rates) and mileage accumulation schedules. The US Federal Test Procedure (FTP) and several short tests were conducted at various stages.

The results of the program indicated that vehicle emissions are mainly affected by the amount of lead passing through the engine and secondarily by the rate of misfueling.

Based on the data, it was possible to develop quantitative relationships between lead consumption and HC, CO and NOx emissions. Emission levels for each of the 29 vehicles involved in the EPA program were normalized to the levels that existed prior to any lead contamination and then plotted as a function of the total amount of lead consumed.

Normalization made it possible to eliminate the influence of different emissions standards. Regression equations were then derived relating HC, CO and NOx emissions respectively to the grams of lead consumed by each vehicle.

Emissions of HC, CO and NOx generally increase steadily with continuous misfueling.

HC emissions increase the most rapidly on a percentage basis, followed by CO and, to a lesser extent, NOx.

Reasonably good correlations exist for the relationship between total lead consumed and emissions increases of each pollutant, especially for HC the pollutant most affected.

In the case of HC, approximately 90% of the variability in emissions can be explained by the lead exposure. More recent data tend to verify these results.