Enhanced emission of intermediate/semi-volatile organic matters in both gas and particle phases from ship exhausts with low-sulfur fuels

Abstract. The widespread utilization of low-sulfur fuels in compliance with global sulfur limit regulations has significantly mitigated the emissions of sulfur dioxide (SO₂) and particulate matter (PM) on ships. However, significant uncertainties still persist regarding the impact on intermediate/semi-volatile organic compounds (I/SVOCs). Therefore, on-board test of I/SVOCs from three ocean-going vessels (OGVs) and four inland cargo ships (ICSs) with low-sulfur fuels (< 0.50 % m/m) in China were carried out in this study. Results showed that the emission factors of total I/SVOCs were 881 ± 487, 1181 ± 421 and 1834 ± 667 mg (kg fuel)^-1 for OGVs with heavy fuel oil (HFO), marine gas oil (MGO) and ICSs with 0# diesel, respectively. The transition from low-sulfur content (< 0.50 % m/m) to ultra-low-sulfur content (< 0.10 % m/m) fuels had evidently enhanced the emission factor of I/SVOCs, with non-ignorable contribution from particle-phase I/SVOCs, thereby further amplifying the secondary organic aerosol formation potential (SOAFP). Fuel type, engine type, and operating conditions comprehensively influenced the emission factor level, composition, and volatility distribution of I/SVOCs. Notably, a substantial proportion of fatty acids had been identified in ship exhausts, necessitating heightened attention. Furthermore, organic diagnostic markers of hopanes, in conjunction with the C_18:0 to C_14:0 acid ratio, could be considered as potential markers for HFO exhausts. The findings suggest that there is a necessity to optimize the implementation of a global policy on ultra-low-sulfur oil in the near future.