Compliance and port air quality features with respect to ship fuel switching regulation: a field observation campaign, SEISO-Bohai

Since 1 January 2017, ships berthed at the core ports of three designated “domestic emission control areas” (DECAs) in China should be using fuel with a sulfur content less than or equal to 0.5 %. In order to evaluate the impacts of fuel switching, a measurement campaign (SEISO-Bohai) was conducted from 28 December 2016 to 15 January 2017 at Jingtang Harbor, an area within the seventh busiest port in the world. This campaign included meteorological monitoring, pollutant monitoring, aerosol sampling and fuel sampling. During the campaign, 16 ship plumes were captured by the on-shore measurement site, and 4 plumes indicated the usage of high-S_F (S_F refers to the sulfur content of marine fuels). The average reduction of the mean ΔNO_x∕ΔSO₂ ratio from high-sulfur plumes (3.26) before 1 January to low-sulfur plumes (12.97) after 1 January shows a direct SO₂ emission reduction of 75 %, consistent with the sulfur content reduction (79 %). The average concentrations of PM_2.5 (particulate matter with a diameter less than 2.5 µm), NO_x, SO₂, O₃ and CO during campaign were 147.85 µg m⁻³, 146.93, 21.91, 29.68 ppb and 2.21 ppm, respectively, among which NO_x reached a maximum hourly concentration of 692.6 ppb, and SO₂ reached a maximum hourly concentration of 165.5 ppb. The mean concentrations of carbonaceous and dominant ionic species in particles were 6.52 (EC – elemental carbon), 23.10 (OC – organic carbon), 22.04 (${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2}-}$), 25.95 (${\mathrm{NO}}_{\mathrm{3}}^{-}$) and 13.55 (${\mathrm{NH}}_{\mathrm{4}}^{+}$) µg m⁻³. Although the carbonaceous species in particles were not significantly affected by fuel switching, the gas and particle pollutants in the ambient air exhibited clear and effective improvements due to the implementation of low-sulfur fuel. Comparison with the prevailing atmospheric conditions and a wind map of SO₂ variation concluded a prompt SO₂ reduction of 70 % in ambient air after fuel switching. Given the high humidity at the study site, this SO₂ reduction will abate the concentration of secondary aerosols and improve the acidity of particulate matter. Based on the enrichment factors of elements in PM_2.5, vanadium was identified as a marker of residual fuel ship emissions, decreasing significantly by 97.1 % from 309.9 ng m⁻³ before fuel switching to 9.1 ng m⁻³ after regulation, which indicated a crucial improvement due to the implementation of low-sulfur fuels. Ship emissions were proven to be significantly influential both directly and indirectly on the port environment and the coastal areas around Bohai Bay, where the population density reaches over 650 people per square kilometer. The results from this study report the positive impact of fuel switching on the air quality in the study region and indicate a new method for identifying the ship fuel type used by vessels in the area.