Abstract. Limiting the fuel sulfur content (FSC) is a widely adopted approach to reduce ship emissions of sulfur dioxide (SO2) and particulate matters (PM) particularly in emission control areas (ECA), but its impact on the emission of volatile organic compounds (VOCs) is still not well understood. In this study, emissions from ships at berth in Guangzhou, south China, were characterized before and after implementing the fuel switch policy with a FSC limit of 0.5 % in the Pearl River Delta ECA in south China. After implementing the fuel switch policy, the emission factors (EFs) of SO2 and PM2.5 for coastal vessels dropped by 78 % and 56 % on average, respectively; the EFs of non-methane hydrocarbons (NMHCs), however, reached 1807 ± 1746 mg/kg, about 15 times that of 118 ± 56.1 mg/kg before implementing the new policy. This dramatic increase in the emission of NMHCs might be largely due to the replacement of high-sulfur residual fuel oil with low-sulfur diesel or heavy oils, which are typically more rich in short-chain hydrocarbons. Moreover, reactive alkenes overtook alkanes to become the dominant group among NMHCs and low carbon number NMHCs, such as ethylene, propene and isobutane, became the dominant species after the new policy. As a result of the largely elevated EFs of reactive alkenes and aromatics after the new policy, for per kilogram of fuel burned, emitted NMHCs had nearly 29 times larger ozone formation potentials (OFPs) and about 2 times higher secondary organic aerosol formation potentials (SOAFPs). Unlike coastal vessels, river vessels in the region used diesel fuels all along and were not affected by the fuel switch policy, but their EFs of NMHCs were even 90 % larger than that of coastal vessels after implementing the new policy, with about 120 % larger fuel-based OFPs and 70–140 % larger SOAFPs. The results from this study suggest that while the fuel switch policy could effectively reduce SO2 and PM emissions and thus help combat PM2.5 pollution, it would also lead to greater emissions of reactive VOCs, that may threatens ozone pollution control in the harbor cities. This change for coastal or ocean-going vessels, along with the large amounts of reactive VOCs from river vessels, raises regulatory concerns for ship emissions of reactive VOCs.
The impact of marine shipping and its DECA control on air quality in the Pearl River Delta, China