Effect of Scrubber and Wet Electrostatic Precipitator on Secondary Aerosol Formation Potential of Marine Engine Exhaust

The number of scrubber installations in the global ship fleet has increased in recent years as a response to tightened sulfur regulations set by the International Maritime Organization. In addition to mitigating sulfur oxides, scrubbers have been shown to provide some added benefits in terms of reducing particles in the exhaust. Recently, it was shown that treating the exhaust gas with a combination of a scrubber and a wet electrostatic precipitator can significantly reduce particle number, mass, and black carbon concentrations in the exhaust of marine engines. In this study, the effect of the system on the secondary aerosol formation potential was investigated. The exhaust aerosol produced during heavy fuel oil combustion readily formed aged particle mass, with the majority of the mass consisting of sulfate. The combination of the scrubber and WESP reduced the aged PM to levels corresponding to air utilized for dilution of the exhaust. For sulfate, the detected reduction efficiency of the system was more than 99%. The system was also effective in reducing primary PM during both heavy fuel oil and marine diesel oil combustion. Reduced primary and aged particle mass concentrations could indicate benefits in terms of PM-related health and visibility effects.