Influence of the surface microlayer on atmospheric deposition of aerosols and polycyclic aromatic hydrocarbons

11 pages, 6 figures.-- Printed version published Jul 2007.Supplementary material available: Dependence of deposition velocity on aerosol size and wind speed (1 page, 1 figure, 1 extra reference).Atmospheric dry deposition is an important process for the introduction of aerosols and pollutants to aquatic environments. The objective of this paper is to assess, for the first time, the influence that the aquatic surface microlayer plays as a modifying factor of the magnitude of dry aerosol deposition fluxes. The occurrence of a low surface tension (ST) or a hydrophobic surface microlayer has been generated by spiking milli-Q water or pre-filtered seawater with a surfactant or octanol, respectively. The results show that fine mode (2.7 μm), even though there is an enhanced deposition due to the surface microlayer for some sampling periods, the effect is not observed consistently. This is due to the importance of gravitational settling for large aerosols, rendering a lower influence of the aquatic surface on dry deposition fluxes. ST (mN m-1) is identified as one of the key factor driving the magnitude of PAH dry deposition fluxes (ng m-2 d-1) by its influence on PAH concentrations in deposited aerosols and deposition velocities (vd, cm s-1). Indeed, vd values are a function of ST as obtained by least square fitting and given by Ln(vd) = -1.77 Ln(ST) + 5.74 (r2 = 0.95) under low wind speed (average 4 m s-1) conditions.S.d.V. acknowledges a predoctoral fellowship from the Catalan Autonomous Government. This work was funded by the Spanish Ministry of Education and Science, and the European Commission through the AMIGOS, MIMOSA and AIRWIN projects.Peer reviewe

Influence of the surface microlayer on atmospheric deposition of aerosols and polycyclic aromatic hydrocarbons

11 pages, 6 figures.-- Printed version published Jul 2007.Supplementary material available: Dependence of deposition velocity on aerosol size and wind speed (1 page, 1 figure, 1 extra reference).Atmospheric dry deposition is an important process for the introduction of aerosols and pollutants to aquatic environments. The objective of this paper is to assess, for the first time, the influence that the aquatic surface microlayer plays as a modifying factor of the magnitude of dry aerosol deposition fluxes. The occurrence of a low surface tension (ST) or a hydrophobic surface microlayer has been generated by spiking milli-Q water or pre-filtered seawater with a surfactant or octanol, respectively. The results show that fine mode (2.7 μm), even though there is an enhanced deposition due to the surface microlayer for some sampling periods, the effect is not observed consistently. This is due to the importance of gravitational settling for large aerosols, rendering a lower influence of the aquatic surface on dry deposition fluxes. ST (mN m-1) is identified as one of the key factor driving the magnitude of PAH dry deposition fluxes (ng m-2 d-1) by its influence on PAH concentrations in deposited aerosols and deposition velocities (vd, cm s-1). Indeed, vd values are a function of ST as obtained by least square fitting and given by Ln(vd) = -1.77 Ln(ST) + 5.74 (r2 = 0.95) under low wind speed (average 4 m s-1) conditions.S.d.V. acknowledges a predoctoral fellowship from the Catalan Autonomous Government. This work was funded by the Spanish Ministry of Education and Science, and the European Commission through the AMIGOS, MIMOSA and AIRWIN projects.Peer reviewe