Using shipboard and satellite measurements we explore the environmental factors affecting the number concentration of aerosols with diameter 100 < D < 1000 nm over a cluster of three mesoscale (~10-100 km) eddies in the North Atlantic. Strongest sensitivity to environmental conditions was found in the 400 < D < 1000 nm size range. In this size range particle concentrations were closely linked to the surface wind speed, indicating in-situ production of sea spray aerosols by wind driven processes. Particle concentrations were also affected by mesoscale variability in oceanic conditions at the vicinity of an anti-cyclonic eddy. In addition, a distinct aerosol population possibly produced at a distance of ~1000-2000 km from the study area was identified. The results highlight the importance of oceanic and atmospheric mesoscale processes in determining the characteristics of aerosols over the marine environment.