AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Effect of Relative Humidity on the Composition and Structure of Ambient Secondary Organic Aerosol Particles from the SOAS Field Campaign
AMY BONDY, Sydney Niles, Rachel O'Brien, Victor Nhliziyo, Steve Bertman, Paul Shepson, Ryan Moffet, Kerri Pratt, Andrew Ault, University of Michigan
Abstract Number: 405 Working Group: Aerosol Chemistry
Abstract During the summer of 2013, atmospheric particles were collected during the Southern Oxidant and Aerosol Study (SOAS) to improve our understanding of how these particles are contributing to a relative cooling regionally through light scattering. Measurements focused on single particle analysis of aerosols collected in Centreville, Alabama, a rural forested location. Secondary organic aerosol (SOA) in particular has been found with varying compositions and liquid-liquid phase separation of components leading to a range of internal structures. These phase separations and structures have been probed using chemical imaging techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). The effect of varying relative humidity (RH) and specifically the number of RH cycles were studied to determine how these factors impacted SOA structure. For this lab-based study, optical microscopy and Raman microspectroscopy were used to image single particles to study size and morphology, as well as analyze the change in functional group signals while the RH was varied. Initially inorganic salts, organonitrate, and organosulfate standards, compounds likely to be present in ambient SOA, were tested in a RH-controlled cell to investigate which functional groups changed as the RH changed. In the second phase of the experiment, SOA particles collected on substrates during SOAS were examined to determine how ambient particles containing multiple chemical species behave under changing RH conditions. The improved understanding of these aerosol particles can be used to explore how sources and atmospheric processing change particle structure, and how the altered optical properties impact air quality and climate on a regional scale.