AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aerosol Morphology Transformations from Humidity Cycling
Thuong Phan, Hemanta Timsina, Dabrina Dutcher, TIMOTHY RAYMOND, Ryan Snyder, Bucknell University
Abstract Number: 558 Working Group: Aerosol Physics
Abstract The magnitude of aerosol effects on climate strongly depends on size, morphology, and interaction with water. An investigation of these characteristics is essential to both assess the impacts of aerosols as well as their laboratory generation methods. In this work, we investigated the impact on the size and morphology of several compounds through the use of mobility sizing and an atomic force microscopy (AFM) imaging combined with humidification cycling. Some pure chemical species exhibited a change in size and morphology after the humidity cycling process while others did not. Some chemicals formed different types of crystals and/or morphologies depending on the drying and rewetting process.
Dry particles were also collected using a PIXE impactor and analyzed under the AFM. For one chemical species, a bimodal size distribution was produced from fast drying of dilute, atomized aerosol. The AFM image of the 28 nm mode of dry particles shows mostly spherical particles while the 110 nm mode image shows a mixture of rounded and sharp-edged particles. The humidity cycled particles were also collected and analyzed under the AFM. These particles consistently produced 50 nm unimodal size distributions. In other words, the particles crystallize to different forms when they are rehumidified and redried, re-arranging their structures and forming only one type of crystal. The effect occurred both when size-selected 28 nm or 110 nm particles were individually sent through the rehumidification and redrying process - the resulting mode was always 50 nm. We conclude that the 28 and 110 nm modes were simply different mobility shapes of the same total mass that were able to restructure to a common 50 nm mobility size upon exposure to a humid atmosphere. These results have implications for all laboratory aerosol generation methods, interpretations from these laboratory studies, and atmospheric aerosol processing transformations.