An optoacoustic black carbon sensor for ship emission monitoring

Black carbon (BC) emitted from ship exhaust has negative impacts on both human health and the climate. Monitoring BC emissions and, potentially, introducing a regulatory framework, will depend on the availability of reliable techniques for the measurement of its emission. Current sensors enabling continuous monitoring are too expensive and require frequent maintenance. We have recently developed a low-cost optoacoustic (OptA) BC sensor, which spatially separates OptA detection from OptA excitation, and demonstrated its performance in the laboratory. The unique chamber-based design of the sensor allows for the spatial separation of its delicate quartz tuning fork (QTF) detector from BC particles, while reaching high sensitivity without the need for filters. In this work, we examine for the first time the sensor operation in a real environment, by implementing it on-board a roll-on-roll-off (RoRo) ferry transporting cargo and passengers (RoPax). We present longitudinal measurements of BC concentrations within the ship’s exhaust. We observe a strong linear correlation (R² = 0.9) between our OptA sensor to an aerosol absorption photometer, used for comparison. BC concentrations of the ships exhaust were measured directly from the funnel and BC emission factors were estimated based on simultaneously measured CO₂ content of the exhaust and the carbon content of the fuel. BC concentrations were found to vary depending on the fuel used, namely, marine gas oil (MGO) and methanol. For the latter significantly reduced BC concentrations were observed. We finally discuss the implications of the technology for low-cost and low-maintenance sensors for on-board BC monitoring and beyond.