Ship aerosol emissions and marine fuel regulations: Impacts on physicochemical properties, cloud activity and emission factors

Preprint, 2023

Marine regulations aim to reduce sulfur and nitrogen exhaust emissions from maritime shipping. Here, two compliance pathways
for reducing sulfur dioxide emissions, fuel sulfur content reduction and exhaust wet scrubbing, are studied for their eects on
physicochemical properties and cloud forming abilities of engine exhaust particles. A test-bed diesel engine was utilized to study
fresh exhaust emissions from combustion of non-compliant, high sulfur content fuel with (WS) and without (HiS) the usage
of a wet scrubber as well as a regulatory compliant, low sulfur content fuel (LoS). Particle number emissions are decreased
by [?] 99% when switching to LoS due to absence of 20-30 nm sulfate particles. While number emissions for WS are also
decreased, a shift in the sulfate mode towards larger sizes was found to increase particle mass emission factors by at least 31%.
Changes in the mixing state induced by the compliance measures are re
ected in the hygroscopicity of the exhaust particles.
Fuel sulfur reduction decreased cloud condensation nuclei emissions by at least 97% due to emissions of primarily hydrophobic
soot particles. Wet scrubbing increased those emissions, mainly driven by changes in particle size distributions. Our results
indicate that both compliance alternatives have no obvious impact on the ice forming abilities of 200 nm exhaust particles.
These detailed results are relevant for atmospheric processes and might be useful input parameters for cloud-resolving models
to investigate ship aerosol cloud interactions and to quantify the impact of shipping on the radiative budget.