Abstract
Abstract. Exhaust emissions from shipping are a major contributor to particle concentrations in coastal and marine areas. Previously, the marine fuel sulfur content (FSC) was restricted globally to 4.5 m/m%, but the limit was changed to 3.5 m/m% at the beginning of 2012 and further down to 0.5 m/m% in January 2020. In sulfur emission control areas (SECA), the limits are stricter: the FSC restriction was originally 1.50 m/m%, but it decreased to 1.00 m/m% in July 2010 and again to 0.10 m/m% in January 2015. In this work, the effects of the FSC restrictions on particle number concentrations (PNCs) and particle number size distributions (NSDs) are studied in the Baltic Sea SECA. Measurements were made on a small island (Utö, Finland; 59∘46′50 N, 21∘22′23 E) between 2007 and 2016. Ship plumes were extracted from the particle number size distribution data, and the effects of the FSC restrictions on the observed plumes as well as on the ambient concentrations were investigated. Altogether, 42 322 analyzable plumes were identified during the 10-year measurement period. The results showed that both changes in the FSC restrictions reduced the PNCs of the plumes. The latter restriction (to 0.10 m/m% in January 2015) also decreased the ambient particle number concentrations, as a significant portion of particles in the area originated from ship plumes that were diluted beyond the plume detection limits. The overall change in the PNCs of the plumes and ambient air was 27 and 32 %, respectively, for the total FSC change from 1.50 m/m% to 0.10 m/m%. The decrease in the plume particle number concentration was caused mostly by a decrease in the concentration of particle sizes of between approximately 33 and 144 nm. The latter restriction also reduced the geometric mean diameter of the particles, which was probably caused by the fuel type change from residual oil to distillates during the latter restriction. The PNC was larger for the plumes measured at daytime than for those measured at nighttime, likely because of the photochemical aging of particles due to UV light. The difference decreased with decreasing FSC, indicating that a lower FSC also has an impact on the atmospheric processing of ship plumes.
Highlights
Particulate matter (PM) from shipping contributes to a significant fraction of PM10, PM2.5, and PM1 in European coastal areas (1 %–7 %, 1 %–14 %, and ≥ 11 %, respectively) (Viana et al, 2014)
Not all of the emissions from these distant shipping lanes are expected to be detected as plumes, as they are probably too diluted to be unidentifiable by the detection method
The main focus of this work was to investigate the effects of the fuel sulfur content (FSC) restrictions on ship plumes; shipping emissions are expected to contribute to the ambient particle number concentrations (PNCtot, including background concentrations, particle number concentration in the plume (PNCpl), and the part of PNCe that was not considered as valid plumes) at Utö
Summary
Particulate matter (PM) from shipping contributes to a significant fraction of PM10, PM2.5,, and PM1 in European coastal areas (1 %–7 %, 1 %–14 %, and ≥ 11 %, respectively) (Viana et al, 2014). In multiple studies, shipping has been reported to be a significant contributor to atmospheric particle number concentrations (PNCs) both in the sea and in coastal areas, especially in the ultrafine size range (Ausmeel et al, 2019; Gobbi et al, 2020; Karl et al, 2020; Kivekäs et al, 2014; Kukkonen et al, 2016; Zanatta et al, 2020). Fuel sulfur content (FSC) has a large effect on the formed particles, and it has been reported to have a strong correlation with particle mass and number concentrations in ship exhaust emissions (Alföldy et al, 2013; Diesch et al, 2013). In sulfur emission control areas (SECAs) the FSC limit is lower and was changed from 1.50 m/m% to 1.00 m/m% in July. The impacts of photochemical aging on ship exhaust plumes are investigated
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