Emission speciation of volatile and intermediate volatility organic compounds from a marine engine: effect of engine load, fuel type and photochemical aging

The enforcement of global fuel sulfur content (FSC) regulations has significantly reduced SO₂ and particulate matter (PM) emissions from ships. However, the impact of the International Maritime Organization's (IMO) sulfur reduction policy on gaseous hydrocarbon emissions, including volatile and intermediate volatility organic compounds (VOCs/IVOCs), remains underexplored. In this study, a 4-stroke single cylinder marine engine was operated using marine gas oil (MGO, FSC = 0.01%) and low-sulfur heavy fuel oil (LS-HFO, FSC = 0.5%) across various engine loads, ranging from 20 kW to a maximum of 80 kW. Emissions were photochemically aged in the oxidation flow reactor “PEAR,” simulating an equivalent photochemical aging period from 1.4 ± 0.2 to 4.6 ± 0.8 days related to the OH· exposure. Emission factors (EFs) of all targeted VOCs/IVOCs varied significantly, ranging from 20.0 ± 2.5 to 180 ± 20 mg kWh⁻¹ and from 26.0 ± 11.0 to 280 ± 100 mg kWh⁻¹ from a high (80 kW) to low engine load (20 kW) for MGO and LS-HFO, respectively. Monoaromatics dominated total fresh emissions for MGO (64%) and LS-HFO (76%), followed by alkanes. Naphthalene and alkylated naphthalene content declined more than monoaromatic and alkane content, thus changing the VOC/IVOC emission pattern after photochemical aging. Estimated SOA from targeted VOC/IVOC precursors accounted for 41% of the measured secondary organic aerosol (SOA) for MGO, while a lower contribution (34%) was observed for LS-HFO at 20 kW engine load, highlighting the role of unmeasured VOCs/IVOCs in SOA formation. Expanding the research on the effects of atmospheric aging on marine emissions will offer valuable insights into this underexplored area.