Abstract
Abstract. Limiting fuel sulfur content (FSC) is a widely adopted approach for reducing ship emissions of sulfur dioxide (SO2) and particulate matter (PM), particularly in emission control areas (ECAs), but its impact on the emissions of volatile organic compounds (VOCs) is still not well understood. In this study, emissions from ships at berth in Guangzhou, southern China, were characterized before and after the implementation of the fuel switch policy (IFSP) with an FSC limit of 0.5 % in the Pearl River Delta ECA (ECA-PRD). After IFSP, the emission factors (EFs) of SO2 and PM2.5 for the coastal vessels decreased by 78 % and 56 % on average, respectively; however, the EFs of the VOCs were 1807±1746 mg kg−1, approximately 15 times that of 118±56.1 mg kg−1 before IFSP. This dramatic increase in the emissions of the VOCs might have been largely due to the replacement of high-sulfur residual fuel oil with low-sulfur diesel or heavy oils, which are typically richer in short-chain hydrocarbons. Moreover, reactive alkenes surpassed alkanes to become the dominant group among the VOCs, and low-carbon-number VOCs, such as ethylene, propene and isobutane, became the dominant species after IFSP. As a result of the largely elevated EFs of the reactive alkenes and aromatics after IFSP, the emitted VOCs per kilogram of fuel burned had nearly 29 times greater ozone formation potential (OFP) and approximately 2 times greater secondary organic aerosol formation potential (SOAFP) than those before IFSP. Unlike the coastal vessels, the river vessels in the region used diesel fuels consistently and were not affected by the fuel switch policy, but the EFs of their VOCs were 90 % greater than those of the coastal vessels after IFSP, with approximately 120 % greater fuel-based OFP and 70 %–140 % greater SOAFP. The results from this study suggest that while the fuel switch policy could effectively reduce SO2 and PM emissions, and thus help control PM2.5 pollution, it will also lead to greater emissions of reactive VOCs, which may threaten ozone pollution control in harbor cities. This change for coastal or ocean-going vessels, in addition to the large amounts of reactive VOCs from the river vessels, raises regulatory concerns for ship emissions of reactive VOCs.
Highlights
World seaborne trade volumes are estimated to account for over 80 % of the total global merchandise trade (UNCTAD, 2016)
The fuel sulfur content (FSC) for the tested coastal vessels decreased from 2.2 ± 0.5 % on average before implementation of the fuel switch policy (IFSP) to 0.4 ± 0.5 % after IFSP, there were some ships, such as ship G, which violated the regulation with an FSC still above the limit of 0.5 % (Table 1)
The ship fuel was transferred from residual fuel oil to diesel oil or heavy oil (Fig. S1 in the Supplement), and the compositions of the fuels used by the coastal vessels tended to have more low-carbon-number hydrocarbons, as demonstrated by their total ion chromatograms, than those of coastal vessels before IFSP (Fig. S2)
Summary
World seaborne trade volumes are estimated to account for over 80 % of the total global merchandise trade (UNCTAD, 2016). An important intervention policy by the International Maritime Organization (IMO) to reduce ship emissions is the designation of emission control areas (ECAs) where a more stringent limit of fuel sulfur content (FSC) is implemented (IMO, 2017). This ECA approach has resulted in significant improvements in ambient air quality for coastal areas (Lack et al, 2011; Tao et al, 2013; Contini et al, 2015; Zetterdahl et al, 2016). With the increasingly stringent control over land-based emissions sources, limiting ship emissions has gradually stood out as an effective measure to control air pollution in coastal zones
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