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Chemiluminescense detectors (CLD) represent well-established instruments to measure the concentrations of the oxides of nitrogen (NOx) in raw as well as diluted automotive exhaust in accordance with the regulations in the United States of America and the European Community. Although the CLD offers the benefits of wide measuring ranges down to low concentrations with a fast response time, its drawbacks are characterized by quenching effects caused by carbon dioxide and water, by an adverse cost-benefit ratio, by the fact that ozone, a highly toxic gas, is necessary for operation, and by additional components needed, such as vacuum pumps and deozonizer. As a consequence, car manufacturers and agencies are looking for alternative analyzers for the measurement of NO in raw exhaust gas. Ultra-violet (UV) analyzers have potential to replace the CLD, as they offer advantages like low noise, no water and CO2 interference, less equipment for operation and reduced costs.

Increasing requirements for the result quality of exhaust emission analyzers and state of the art analyzer technology require a new point of view regarding measuring range definitions and linearization procedures. To make best use of the power of this analyzer technology, linearizaton procedures need reconsideration. Although for certification the linearization procedures to be applied on an emission analyzer are define clearly, for research and development applications, no prescriptions are existing. Therefore non sophisticated routines, that assist the full potential of new analyzers may be employed.

Bag emission measurements on Ultra Low Emission Vehicles require measurement sensitivities in the 1 ppm range for HC and NOx and measurement resolutions well below this to obtain sufficient accuracy and repeatability. Additionally, an analysis of the C2 to C12 components is required. In these emission ranges, adsorption, desorption, diffusion and chemical reaction processes may produce significant effects to the measuring values. Therefore, improvements are necessary to avoid this as far as possible. However, for physical reasons these effects cannot be eliminated completely. For example: Particle filters are not 100% efficient and particles will slowly contaminate the surfaces. Due to physical and chemical processes with some gas components, even stainless steel and Teflon can change their characteristics. Problems resulting from the physical and chemical effects and provisions to minimize the influences to the measuring accuracy and system stability are discussed.