Sources, nature and influence on climate of marine airborne particles

Airborne particles (aerosol) collected at Cape Grim, Tasmania, in February 2006 in baseline conditions were examined by transmission electron microscopy. Particles recognised as marine exopolymer gels, and aggregates of insoluble organic particles that have diameters of similar to 40 nm, formed 9% of the particles larger than 200 nm. Once watersoluble compounds were removed by dialysis, the proportion rose to 30%. The gels and exopolymers were mainly of marine algal and bacterial origin. Their highly surface-active properties make them potentially environmentally important in the aerosol because of their ability to act as cloud condensation nuclei. The chemical constitution of particles in the 80-200-nm diameter size range is controversial, and widely varying estimates of the proportion of sea salt they contain have been published. Possible reasons for this are discussed. The present work supports the lowest estimate.