AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Aerosols over the Remote Forest Regions of Amazonia and Siberia Investigated by STXM-NEXAFS
MEINRAT O ANDREAE, Christopher Pöhlker, Paulo Artaxo, Eugene Mikhailov, Alexey Panov, Arthur L. D. Kilcoyne, Ulrich Pöschl, Bärbel Sinha, Kenia T. Wiedemann, Max Planck Institute for Chemistry
Abstract Number: 14 Working Group: Remote and Regional Atmospheric Aerosols
Abstract We investigated the morphology and chemical composition of aerosol samples from remote forest environments in the Amazon Basin and Central Siberia, using Scanning Transmission X-ray Microscopy - Near Edge X-ray Absorption Fine Structure (STXM-NEXAFS) analysis in combination with other microanalytical techniques. The NEXAFS spectra were used to estimate the elemental ratios of C, N and O, as well as the chemical bonding state of these elements. In addition, we characterized the distributions of some other elements, such as K, Ca, and Fe. The aim of this study was to investigate the microphysical and chemical properties of remote background aerosols and their internal mixing state. The samples were collected over several seasons at both sites and represent a range of conditions, from nearly pristine background to anthropogenically polluted.
The Amazonian aerosol during the rainy season was found to be dominated by drop-like organic particles in the fine mode (often in internal mixture with solid particles), and Primary Biological Aerosol Particles (PBAP) in the coarse mode. Liquid organic aerosol coatings were also frequently observed on the PBAPs. Unexpectedly, most SOA particles showed the presence of variable amounts of K, with K mass fractions decreasing with increasing particle size. Furthermore, the spectra exhibit characteristic signal patterns for different functional groups. In most cases, the spectrum near the C-edge is dominated by either the hydroxyl or the carboxylate signal, but prominent peaks for ketone carbonyls, alkanes and alkenes have also been observed. During the dry season, particle number concentrations were 2-3 times higher than in the wet season, and soot particles, often in internal mixture with organics and inorganic ions were frequent. K-rich particles were less abundant than during the rainy season, but (presumably biogenic) SOA still formed a considerable part of the aerosol population.
Over Siberia, large PBAPs were much less frequent than over the Amazon forest, whereas soil dust and combustion-related particles were common constituents of the coarse fraction. In the fine fraction, pollution related particles were always present and usually dominant, as evidenced by the presence of ammonium sulfate and soot carbon. SOA usually occurred as internal mixture with ammonium sulfate. Our results document the pervasive influence of anthropogenic emissions even in the most remote parts of the continental atmosphere.