New data concerning the chemical composition of atmospheric aerosol particles in two radial size-ranges, 0.08 < r < 0.8 µ and 0.8 < r < 8 µ, were obtained during a four-week period on the Atlantic coast. The samples were analyzed for the five components, Na+, Cl−, SO4−−, NH4+, NO3−, and later also for NO2−, ClO3− and Mg++. The large particles, with 0.08 < r < 0.8 µ, consisted nearly entirely of sulfate and ammonia, as was found in previous investigations in central Europe. Besides these substances, the giant particles, with 0.8 < r < 8 µ, contained variable, though sometimes considerable, amounts of nitrate and sodium chloride. Up to wind speeds of at least Beaufort 5, the production of sea-salt particles seems thus to be limited to radii above 0.8 µ. The components NO2−, ClO3− and Mg++ were not found to be present above the limit of detection.