Articles | Volume 17, issue 12
Research article
20 Jun 2017
Research article |  | 20 Jun 2017

Impact of North America on the aerosol composition in the North Atlantic free troposphere

M. Isabel García, Sergio Rodríguez, and Andrés Alastuey

Abstract. In the AEROATLAN project we study the composition of aerosols collected over  ∼  5 years at Izaña Observatory (located at  ∼  2400 m a.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-10 µm aerosols (PM10) carried by westerly winds to Izaña, after transatlantic transport, are typically within the range 1.2 and 4.2 µg m−3 (20th and 80th percentiles). The main contributors to background levels of aerosols (PM10 within the 1st–50th percentiles  =  0.15–2.54 µg m−3) are North American dust (53 %), non-sea-salt sulfate (14 %) and organic matter (18 %). High PM10 events (75th–95th percentiles  ≈  4.0–9.0 µg m−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.

Short summary
We measured the composition of the aerosols linked to transatlantic transport from North America to Izaña Observatory, Tenerife. The eastward-moving depressions prompt aerosols export. The seasonal shift of the westerlies stream over the aerosol sources prompts seasonality in the aerosol composition. High loads of dust, organics and sulfate occur in spring and elemental carbon occurs in summer. Aerosol population in the westerly winds over the North Atlantic is dominated by dust and organics.
Final-revised paper