When:       Friday 8 February 2013

Time:         11h30

Venue:      The Avogadro, Chemistry Building, Room 3.22

Organic aerosols (OA) are ubiquitous in the atmosphere and play important roles in the climate system. They can cool Earth’s surface by scattering sunlight or serve as nuclei for water droplets and ice crystals in clouds and precipitation. The properties and origin of organic aerosol particles are, however, still poorly understood, and their effects are among the largest uncertainties in the current understanding of climate. One of the few continental regions where aerosols can be studied under near-natural conditions is the Amazon Basin. We applied scanning transmission X-ray microscopy with near edge X-ray absorption fine structure (STXM-NEXAFS) analysis to investigate the morphology, mixing state and chemical composition of aerosol samples from the Amazon Basin. The Amazonian OA particles comprised a mixture of homogeneous droplets and droplets having internal structures due to atmospheric aging. In spite of the similar morphological appearance, the Amazon samples showed considerable differences in elemental and functional group composition. As an unexpected finding, the NEXAFS spectra revealed clearly resolved potassium (K) signals for all analyzed particles in addition to the dominant organic component. During the rainy season and in the absence of anthropogenic influence, active biota is regarded to be the major potassium source. The direct influence of rainforest biota on the number concentration of cloud condensation nuclei may be important for the development of the Amazonian rainforest ecosystem, and it may also be generally relevant for the evolution of ecosystems and climate on global scales and in the Earth’s history.

Contact person: Dr Patricia Forbes, Ph: (012) 420 5426