The southeast United States has been cooling in comparison to the rest of the U.S. due secondary organic aerosol (SOA) formed from the interaction of biogenic and anthropogenic aerosol sources. To study this phenomenon the Southern Oxidant and Aerosol Study (SOAS) took place in southeast United States during the summer of 2013. Impacted particles were collected during SOAS and complex liquid-liquid phase separation was observed using scanning electron microscopy (SEM) and scanning transmission x-ray microscopy near edge x-ray absorption fine structure (STXM-NEXAFS). In many particles, inorganic and organic phases within the particles were neither homogeneously mixed nor in a core shell structure indicating that a more viscous organic phase may be present. Image processing of SEM images of aerosol particles from the study was used to quantify the internal structure complexity of SOA particles and their day-to-day variability. Additionally, laboratory-based experiments using ammonium sulfate with either alpha-4-dihydroxy-3-methoxy-benzeneacetic acid (HMMA) or poly ethylene glycol (PEG-400), were used to examine the relationship between relative humidity (RH) and the complexity of the internal structure of SOA particles to gain a more thorough understanding of the phenomena observed from SOAS. Organic-inorganic mixed particles were atomized, impacted, and then subjected to different numbers of RH cycles to determine whether increasing and decreasing water content changed internal structure. As the particles were subjected to a greater number of RH cycles, the internal structure complexity increased, suggesting that there is a relationship between RH and the complexity of the internal structure of SOA. This analysis can be used to provide insight into the optical properties of organic-inorganic mixtures in the atmosphere, and thus their impact on climate.

Secondary organic aerosol (SOA): Analyzing degree of internal complexity and effect of changing relative humidity (RH)

251st National Meeting (2016)

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