Single Particle Analysis of Atmospheric Aerosol Particles

Atmospheric aerosol particles show large spatial and temporal variations in their properties and concentrations which are caused by parameters such as the short life-time, varying source properties and source strength as well as transformations during transport. Airborne particulate matter (PM) is therefore a complex mixture of many different chemical species originating from a variety of sources both of natural (forest fire, desert dust) and anthropogenic origin (industrial emissions, road traffic, domestic heating). Aerosol particles are still one of the major uncertainty factors for the assessment of climate change as well as of their effects on human health and the built environment, including cultural heritage monuments and buildings.

The project aims investigating aerosol particle shape, mixing state, morphology and elemental  composition  based on single particle analysis using Scanning Electron Microscopy coupled with Energy Dispersive Analysis (SEM+EDS). It is the first time that such a work is performed in Portugal. This work would benefit from and complement to the ongoing FCT funded project PTDC/AAC-CLI/104925/2008 entitled “Aerosol composition in Southwestern Iberia: properties and sources”.

The analytical approach in this project has been proven as one of the most suitable for the characterization of the elemental composition for source apportionment of PM, in general more useful than the bulk elemental composition, also with respect to their potential effects on human health. The unique capabilities of SEM+EDS will allow for the particle-size-resolved collection of elemental composition data. This information is essential for the identification of the particles and their source-apportionment.  Furthermore, it can help to identify mineralogical phases. For example, heavy metals (such Cu, Zn, Ni) or other elements (such as Pb and/or  Br) may be used to distinguish road traffic aerosol sources from other sources, whereas the presence of V may be indicative of oil as opposed to coal fossil fuel combustion sources. For selected particles, the spatial 2D distribution of the elements will be obtained by elemental mapping. This provides the mixing state of the particles and, therefore, can yield more information of the particle’s atmospheric processing history. The analytical work will be distributed between the Institute of Applied Geosciences (Darmstadt University of Technology) and the Centro de Geofisica of the University of Evora. In Germany, a low vacuum FEI Quanta FEG ESEM electron microscope with capability to decrease the loss of volatile matter will be used. In Portugal, a Hitachi S-3700N LV SEM interfaced with a Bruker X-Flash EDS and software for automated particle analysis is available.

The project inherently envisages frequent exchange visits between core members of the Portuguese and German teams to share experiences and to discuss analytical problems arising from the monitoring campaigns. It would therefore greatly benefit from the extra funding for travel available through this Acçôes Integradas Luso-Alemanha program.