The Use of STIM and PESA to Measure Proles of Aerosol Mass and Hydrogen Content, Respectively, across Mylar Rotating Drums Impactor Samples

A method has been developed for measuring proŽ les of aerosol mass on thin (480 1g/cm2) Apiezon-L coatedMylar Ž lms employed in rotating drum aerosol impactor samplers using the ion beam analysis technique scanning transmission ion microscopy (STIM). The greased Mylar Ž lms are excellent impaction substrates and possess excellent uniformity in projected density, making them an ideal substrate for STIM analysis. The uniformity in projected density of a Ž lm enables STIM with a 3 MeV proton beam to produce proŽ les of aerosol mass with an accuracy of better than 90% and a mass sensitivity approaching 10 1g/cm2. Further, we have extended proton elastic scattering analysis (PESA) to the same Ž lms, achieving measurement of an organic surrogate. Although the Ž lms contain » 20 1g/cm2 hydrogen, the spatial uniformity in Ž lm hydrogen content enables PESA with a 3 MeV proton beam to produce proŽ les of hydrogen arising solely from the aerosols with an accuracy to within § 1 1g/cm2 and a mass sensitivity of » 1 1g/cm2. These measurements when combined with synchrotron-x-ray  uorescence (S-XRF) measurements on the same Ž lm allow mass closure, sum of species versus measured mass, a key quality assurance protocol, to be approached. All 3 techniques were applied to very Ž ne and ultra-Ž ne particles collected in Fresno, CA, November, 2000 by slotted DRUM samplers. Temporal resolution in the resulting proŽ les was · 6 h. The dramatic changes in composition versus size and time, and new types of elemental correlations unseen in PM2.5 Ž lters, will be major assets in correlating