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As automotive exhaust emission levels reduce, there is a need for increased sensitivity of the NOx measurement. This paper documents work performed to increase the sensitivity of the existing Rosemount NGA 2000 CLD Analyzer. The effects of sample flow rate, ozone flow rate and ozone supply gas were explored. Limit of Detection (LOD) and Converter Efficiency were evaluated. The goal of this optimization has been to provide a cost effective and expeditious method to improve the low level NOx measurement. Changing the ozone generator supply gas from air to oxygen and increasing the sample and ozone flow rates resulted in a LOD improvement from 17 ppb to 8 ppb.

Certification of flex-fueled vehicles to US Environmental Protection Agency (EPA) and California Air Resources Board (CARB) emission standards requires a flame ionization detector (FID) analysis for hydrocarbons, plus a separate analysis for alcohols. Alcohol analysis methods, such as those found in the California Non-Methane Organic Gas (NMOG) Test Procedures and in the Code of Federal Regulations (40 Part 86), involve the bubbling of vehicle sample gas (exhaust or evaporative) through sample impingers filled with water. The water is then analyzed by gas chromatography (GC) equipped with a FID. This method requires significant manual sample handling and transport, and may take many hours for analysis to be complete. After analysis is completed, the vehicle test results are post-processed, sometimes manually, to generate the final sample results. This report describes the direct bag analysis of ethanol with a photoacoustic gas analyzer.