Real-world emission characteristics of VOCs from typical cargo ships and their potential contributions to SOA and O₃ under low-sulfur fuel policies

Abstract. Mandatory use of low-sulfur fuel according to global sulfur limit regulation has reduced the emissions of SO2 and PM significantly on ships, while it also leads to very large uncertainty on VOCs emission. Therefore, on-board test of VOCs from 9 typical cargo ships with low-sulfur fuels in China were carried out in this study. Results showed that emission factor of VOCs (EFVOCs) varied largely from 0.09 to 3.01 g kg-1 fuel, with domestic coastal cargo ships (CCSs) had the highest levels and ocean-going vessels (OGVs) the lowest. The switch of fuels from heavy fuel oil (HFO) to diesel increased EFVOCs by 48 % on average, which enhanced both O3 and secondary organic aerosol (SOA) formation potentials, especially for OGVs. Besides, the use of low-sulfur fuels for OGVs also lead to significant increase of naphthalene emission. These indicated the implementation of globally ultra-low-sulfur oil policy in the near future needs to be optimized. Moreover, aromatics were the most important common contributors to O3 and SOA in ship exhausts, which need to be controlled with priority. It was also found that benzene, toluene, and ethylbenzene ratio of 0.5:0.3:0.2 on average could be considered as a diagnostic characteristic to distinguish ship emission from other emission sources.