Abstract. In the AEROATLAN project we study the composition of aerosols collected over  ∼ 5 years at Izaña Observatory (located at  ∼ 2400ma.s.l. in Tenerife, the Canary Islands) under the prevailing westerly airflows typical of the North Atlantic free troposphere at subtropical latitudes and midlatitudes. Mass concentrations of sub-10µm aerosols (PM₁₀) carried by westerly winds to Izaña, after transatlantic transport, are typically within the range 1.2 and 4.2µgm⁻³ (20th and 80th percentiles). The main contributors to background levels of aerosols (PM₁₀ within the 1st–50th percentiles = 0.15–2.54µgm⁻³) are North American dust (53%), non-sea-salt sulfate (14%) and organic matter (18%). High PM₁₀ events (75th–95th percentiles  ≈ 4.0–9.0µgm⁻³) are prompted by dust (56%), organic matter (24%) and non-sea-salt sulfate (9%). These aerosol components experience a seasonal evolution explained by (i) their spatial distribution in North America and (ii) the seasonal shift of the North American outflow, which migrates from low latitudes in winter (∼ 32°N, January–March) to high latitudes in summer (∼ 52°N, August–September). The westerlies carry maximum loads of non-sea-salt sulfate, ammonium and organic matter in spring (March–May), of North American dust from midwinter to mid-spring (February–May) and of elemental carbon in summer (August–September). Our results suggest that a significant fraction of organic aerosols may be linked to sources other than combustion (e.g. biogenic); further studies are necessary for this topic. The present study suggests that long-term evolution of the aerosol composition in the North Atlantic free troposphere will be influenced by air quality policies and the use of soils (potential dust emitter) in North America.