Ship plumes in the Baltic Sea Sulfur Emission Control Area: chemical characterization and contribution to coastal aerosol concentrations

Abstract

In coastal areas, there is increased concern about emissions from shipping activities and the associated impact on air quality. We have assessed the ship aerosol properties and the contribution to coastal particulate matter (PM) and nitrogen dioxide (NO₂) levels by measuring ship plumes in ambient conditions at a site in southern Sweden, within a Sulfur Emission Control Area. Measurements took place during a summer and a winter campaign, 10 km downwind of a major shipping lane. Individual ships showed large variability in contribution to total particle mass, organics, sulfate, and NO₂. The average emission contribution of the shipping lane was 29±13 and 37±20 ng m⁻³ to PM_0.5, 18±8 and 34±19 ng m⁻³ to PM_0.15, and 1.21±0.57 and 1.11±0.61 µg m⁻³ to NO₂, during winter and summer, respectively. Sulfate and organics dominated the particle mass and most plumes contained undetectable amounts of equivalent black carbon (eBC). The average eBC contribution was 3.5±1.7 ng m⁻³ and the absorption Ångström exponent was close to 1. Simulated ageing of the ship aerosols using an oxidation flow reactor showed that on a few occasions, there was an increase in sulfate and organic mass after photochemical processing of the plumes. However, most plumes did not produce measurable amounts of secondary PM upon simulated ageing.