Carbon Dioxide (CO2) Tracer Technique for Modal Mass Exhaust Emission Measurement

The CO₂ tracer technique is a method of measuring automotive exhaust mass emissions during arbitrary modes of operation of a car on the 1972 federal emission test driving schedule. This technique allows modal mass measurements of low-emission cars based on undiluted exhaust gas concentrations. The CO₂ concentration at the tailpipe is compared with the CO₂ in the diluted stream to obtain exhaust flow. This flow, multiplied by tailpipe concentrations of hydrocarbon, carbon monoxide, and nitric oxide, and integrated over the driving mode, gives modal mass emissions. Problems associated with the lag between the time at which a transient maneuver takes place in the engine and the time at which measurements are recorded are also discussed.