DEPTH-RESOLVED CHEMICAL-ANALYSIS OF ENVIRONMENTAL MICROPARTICLES BY SECONDARY MASS-SPECTROMETRY

Secondary neutral and ion mass spectrometry (SNMS and SIMS) have been used for the depth-resolved analysis of environmental microparticles dispersed in outdoor-air. Although these particles contain a variety of ionic and molecular compounds, elemental quantitation has been found possible using plasma-based SNMS. Detection limits down to a few ppm and a depth resolution reaching about 20 nm have been attained. The total elemental composition is given for aerosol particles sampled in the vicinity of a busy highway. Matrix-dependent effects limit the accuracy to about +/- 40%. The measured variation of erosion rates for different materials allows an estimation of the depth scale with a similar accuracy. Analysis of submicron aerosol particles shows carbon compounds to be enriched within an outer layer of 200 nm. The measurement of the CH cluster reveals the content of organic hydrogen to be also increasing towards the surface. Dynamic SIMS is employed for chemical characterization. Ammonium sulfate is found to be the major component inside the particles. Sodium nitrate was identified within more coarse particles.