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 d ispersed 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 a nd a depth resolution reaching about 20 nm have been attained. The tot al elemental composition is given for aerosol particles sampled in the vicinity of a busy highway. Matrix-dependent effects limit the accura cy to about +/- 40%. The measured variation of erosion rates for diffe rent materials allows an estimation of the depth scale with a similar accuracy. Analysis of submicron aerosol particles shows carbon compoun ds 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 incr easing towards the surface. Dynamic SIMS is employed for chemical char acterization. Ammonium sulfate is found to be the major component insi de the particles. Sodium nitrate was identified within more coarse par ticles.