In-situ tailpipe soot emission monitoring for diesel engine exhaust using a quartz-enhanced photoacoustic spectroscopy sensor

An in-situ soot sensor for monitoring diesel engine exhaust in real-time has been developed and demonstrated in a very cold climate and high soot concentration environment. While existing exhaust gas measurements require either a sampling process or an additional conditioning system, the proposed sensor measures the exhaust gas directly while compensating for soot accumulation. The sensor's signal-to-noise ratio was improved through a combination of off-beam alignment, and acoustic micro-resonators. The sensor was calibrated in a laboratory environment using an optical particle counter (OPC) and a linear correlation of soot mass concentration and optical absorption was established. A single measurement takes about 1.3 s to complete including the analysis, while the measurement uncertainty and the minimum detection limit of the sensor were 0.134 × 10⁴ μg/m³ and 0.268× 10⁴ μg/m³, respectively. The sensor was then used to measure soot concentration of the diesel engine exhaust gas in Ulaanbaatar, Mongolia, during winter where it was used to measure soot concentration from exhaust manifold of several buses with varying levels of diesel particulate filter degradation. Overall, the proposed sensor provided unique advantages compared to existing soot sensors such as specificity and portability as well as being uniquely optimized for the intended environmental conditions.