Black Carbon in the Marine Atmosphere: Concentration and Mixing State From Coastal to Remote Atlantic Regions

Abstract Black carbon (BC) from maritime emissions plays a critical role by influencing radiation, cloud processes, and atmospheric dynamics in the marine atmosphere. These impacts depend on BC concentration and mixing state with other aerosol components. However, in situ observations of BC over oceans remain scarce, and the influence of the marine environment on the evolution of BC mixing state is not well understood. Here, we present shipborne measurements aboard the research sailing yacht S/Y Eugen Seibold during 10 Atlantic Ocean cruises. The data set spans 1,120 of measurement hours from near‐coastal regions to remote ocean areas. In oceanic regions extending from tens to thousands of kilometers offshore, 1‐min averaged BC concentrations were typically around 100 ng m −3 , suggesting a well‐mixed marine background. Despite the relatively small variability in BC mass concentrations, the mixing state of BC exhibits substantial differences between nearshore and remote oceanic regions. High number fractions (>50%) of BC particles without core‐shell morphologies, characterized by BC externally attached to non‐BC materials, were observed in near‐coastal regions and decreased to ∼20% in remote oceanic regions. In ship‐impacted regions, small freshly emitted BC particles tend to coagulate with other aerosol particles and forming non‐core‐shell attached structures, while high relative humidity (RH > 85%) tends to promote the formation of thick coatings. Our results provide new insights into climate‐relevant properties and underscore the importance of coagulation and hygroscopic processing for the mixing state of BC in the marine atmosphere.