NUCLEAR MICROPROBE ANALYSIS AND SOURCE APPORTIONMENT OF INDIVIDUAL ATMOSPHERIC AEROSOL-PARTICLES

In atmospheric aerosol research, one key issue is to determine the sou rces of the airborne particles. Bulk PIXE analysis coupled with recept or modeling provides a useful, but limited view of the aerosol sources influencing one particular site or sample. The scanning nuclear micro probe (SNM) technique is a microanalytical technique that gives unique information on individual aerosol particles. In the SNM analyses a 1. 0 mum size 2.4 MeV proton beam from the Oxford SNM was used. The trace elements with Z > 11 were measured by the particle induced X-Tay emis sion (PIXE) method with detection limits in the 110 ppm range. Carbon, nitrogen and oxygen are measured simultaneously using Rutherford back scattering spectrometry (RBS). Atmospheric aerosol particles were coll ected at the Brazilian Antarctic Station and at biomass burning sites in the Amazon basin tropical rain forest in Brazil. In the Antarctic s amples, the sea-salt aerosol particles were clearly predominating, wit h NaCl and CaSO4 as major compounds with several trace elements as Al, Si, P, K, Mn, Fe, Ni, Cu, Zn, Br, Sr, and Pb. Factor analysis of the elemental data showed the presence of four components: 1) soil dust pa rticles; 2) NaCl particles; 3) CaSO4 with Sr; and 4) Br and Mg. Stront ium, observed at 20-100 ppm levels, was always present in the CaSO4 Pa rticles. The hierarchical cluster procedure gave results similar to th e ones obtained through factor analysis. For the tropical rain forest biomass burning aerosol emissions, biogenic particles with a high orga nic content dominate the particle population, while K, P, Ca, Mg, Zn, and Si are the dominant elements. Zinc at 10-200 ppm is present in bio genic particles rich in P and K. The quantitative aspects and excellen t detection limits make SNM analysis of individual aerosol particles a very powerful analytical tool.