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

摘要

A method has been developed for measuring profiles of aerosol mass on thin (480 #mU#g/cm~2) Apiezol-l coated Mylar films employed in rotating drum aerosol impactor samplers using the ion beam analysis technique scanning tramission ion microscopy (STIM). The greased Mylar films are excellent impaction substrates and possess excellent uniformity in projected density, making them an ideal substrate for STM analysis. The uniformity in project ed density of a film enables STIM with a 3 MeV proton beam to produce profiles of aerosol mass with an accuracy of better than 90 and a mass sensitivity approaching 10 #mu#g/cm~2. Further, we have extended proton elastic scattering analysis (PESA) to the same films, achieving measurement of an organic surrogate. Although the films contain approx 20 #mu#g/cm~2 hydrogen, the spatial uniformity in film hydrogen content enables PESA with a 3 MeV proton beam to produce profiles of hydrogen arising solely from the aerosols with an accuracy to within (+-) 1 #mu#g/cm~2 and a mass sensitivity of approx 1 #mu#g/cm~2. These measurements when combined with synchrotron-x-ray fluorescence (S-XRF) measurements on the same film allow mass closure, sum of species versus measured mass, a key quality assurance protocol, to be approached. All 3 techniques were applied to very fine and ultra -fine particles collected in Frenso, CA, November, 2000 by slotted DRUM samplers. Temporal resolution in the resulting profiles was < = 6 h. The dramatic changes in composition versus size and time, and new types of elemental correlations unseen in PM_2.5 filters, will be major assets in correlating aerosols and health impacts, visibility degradation, and the effects of aerosols on colimate.