Particles from the Minneapolis atmosphere were segregated according to hygroscopicity using a tandem differential mobility analyzer (TDMA) and collected with a specially designed aerodynamic focusing impactor for elemental analysis. Areal deposit densities obtained using the focusing impactor are up to a factor of 100 greater than those obtained using a conventional single-jet impactor, thereby reducing required sampling times by the same factor. A Philips CM30 scanning transmission electron 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 μm summertime aerosols examined in this study, less hygroscopic particles included chain agglomerates (~ 55%), irregular shapes (~ 33%), spheres and flakes (< 10% each) and contained mostly carbon, while more hygroscopic particles were liquid droplets that contained sulfur and sometimes carbon or ionic species such as sodium or potassium.
Bibliographical noteFunding Information:
Acknowledgments This research was supported by the Electric Power Research Institute (Grant No. EPRI RP2023-11) and by a U.S. DOE Graduate Fellowship for the Global Change Program (ML). Components of the aerodynamic focusing impactor were purchased with funds provided by a grant from Applied Materials.
- Aerosol water content
- Chemical composition
- Electron microscopy impactor
- Hygroscopic growth
- Mixing characteristics