The analysis of gaseous emissions from ULEV and SULEV automobiles requires very high levels of purity in the gases used for sample dilution, system purging, analyzer operation and analyzer calibration. These gases include as a minimum air, nitrogen, oxygen, hydrogen and helium.
The quality of these gases will vary depending on the “delivery system” - the method of generation, the quality of the distribution system and the type of storage. Methods of delivery range from “on site” gas generation to pressurized gas cylinders or cryogenic liquid storage. Distribution systems include tubing of carbon steel, copper, polymers or stainless steel.
Regardless of the method of delivery, the gas quality can vary. Increasingly stringent emission standards demand reduced variation in gas quality to improve test repeatability and accuracy. Variation can be reduced by either maintaining the quality at a fixed level of undesirable constituents, or by complete removal of all undesirable constituents via appropriate gas treatment.
Selected gas treatment methods were tested to demonstrate “part per billion” level concentrations of the undesirable constituents in gases relevant to emissions analysis.