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

Abstract

Mandatory use of low-sulfur fuel according to the global sulfur limit regulation has reduced the emissions of SO2 and particulate matter (PM) significantly on ships, and it also leads to a very large uncertainty in volatile organic compound (VOC) emissions. Therefore, an on-board test of VOCs from nine typical cargo ships with low-sulfur fuels in China was carried out in this study. Results showed that the emission factor of VOCs (EFVOCs) varied largely from 0.09 to 3.01 g kg−1 of fuel, with domestic coastal cargo ships (CCSs) having the highest level, followed by inland cargo ships (ICSs) and ocean-going vessels (OGVs). 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 potential, especially for OGVs. Besides, the use of low-sulfur fuels for OGVs also led to a significant increase in naphthalene emission. These indicated that the implementation of a global 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 as a matter of priority. It was also found that the benzene, toluene, and ethylbenzene ratio of 0.5:0.3:0.2 on average could be considered a diagnostic characteristic to distinguish ship emissions from other emission sources.