Photoacoustic analyzer for the artifact-free parallel detection of soot and NO ₂ in engine exhaust

Soot particles and NO ₂ are among the most hazardous emissions from diesel combustion engines. Currently, no analytical system exists which allows for the simultaneous, time-resolved online analysis of these two components. Furthermore, state-of-the-art NO ₂ analyzers for exhaust gas require particle filtration prior to the analysis, which may induce artifacts and measurement errors. We present a photoacoustic instrument which overcomes these drawbacks. The sensitivity of the instrument (LODNO ₂ = 0.3 ppm, LOD _soot = 0.54 μg m ^-3, limit of detection/quantification) as well as the temporal resolutions are dictated by the needs of typical automotive applications. Also required for this specific application, we developed PA cells which can be heated to 80 °C, while the microphones maintain a temperature of 45 °C. Setup and specific parameters of the instrument are discussed, and the results of typical engine tests are compared to reference analytical instrumentation.