Spectro-microscopy of Ambient Aerosol Particles: Water Vapor Uptake from the Southern Great Plains site & Preliminary Results from GoAmazon

Description

We present a novel method to measure the mass-based hygroscopicity of particles while characterizing their elemental and carbon functional group compositions. Since mass-based hygroscopicity is insensitive to particle geometry, it is advantageous for probing the hygroscopic behavior of atmospheric particles, which can have irregular morphologies. Combining scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDX), scanning transmission X-ray microscopy (STXM) analysis, and in situ STXM humidification experiments, this method was validated using laboratory-generated, atmospherically relevant particles. Then, the hygroscopicity and elemental composition of 15 complex atmospheric particles were analyzed by leveraging quantification of C, N, and O from STXM, and complementary elemental quantification from SEM/EDX. We found three types of hygroscopic responses, and correlated high hygroscopicity with Na and Cl content. The mixing state determined for 158 particles broadly agreed with those of the humidified particles, indicating the potential to infer the atmospheric hygroscopic behavior from a selected subset of particles. During the second intensive portion of the DOE GoAmazon campaign we collected samples at the T3 and ZF2 sites for subsequent single particle and other analyses. Single particle spectro-microscopy techniques (STXM/NEXAFS & CCSEM/EDX) are used to measure the composition and mixing state of the ensemble of aerosol particles collected at the T3 site during reports of particle “rebound” and “no rebound”. In collaboration (A. Batemen, S. Martin- Harvard, K. Adachi-Japan, & P. Buseck-Arizona) samples containing only the rebound particles were analyzed. These preliminary results show that this sample has a mixing state distinctly different the “full ensemble” samples that contained all particle types including those that rebounded as well as those that didn’t. The “rebound” sample contains mostly partiles that fall into the organic carbon + elemental carbon mixing state. These particles substantial sp2 hybridization (C=C bonds), however, they lack soot inclusions.