Ph. Mcmurry et al., ELEMENTAL COMPOSITION AND MORPHOLOGY OF INDIVIDUAL PARTICLES SEPARATED BY SIZE AND HYGROSCOPICITY WITH THE TDMA, Atmospheric environment, 30(1), 1996, pp. 101-108
Particles from the Minneapolis atmosphere were segregated according to
hygroscopicity using a tandem differential mobility analyzer (TDMA) a
nd collected with a specially designed aerodynamic focusing impactor f
or elemental analysis. Areal deposit densities obtained using the focu
sing impactor are up to a factor of 100 greater than those obtained us
ing a conventional single-jet impactor, thereby reducing required samp
ling times by the same factor. A Philips CM30 scanning transmission el
ectron microscope (STEM) equipped with an EDAX super ultra-thin-window
detector was used to analyze for carbon and heavier elements. For the
limited sample of 0.3-0.4 pm summertime aerosols examined in this stu
dy, less hygroscopic particles included chain agglomerates (similar to
55%), irregular shapes (similar to 33%), spheres and flakes (< 10% ea
ch) and contained mostly carbon, while more hygroscopic particles were
liquid droplets that contained sulfur and sometimes carbon or ionic s
pecies such as sodium or potassium.