Diverse Chemical Mixing States of Aerosol Particles in the Southeastern United States

Abstract

Abstract. Aerosols in the atmosphere are chemically complex with thousands or more chemical species distributed in different proportions across individual particles in an aerosol population. An internal mixing 15 assumption, with species present in the same proportions across all aerosols, is used in many models and calculations of secondary organic aerosol (SOA) formation, cloud activation, and aerosol optical properties. However, many of these effects depend on the distribution of species within individual particles, and important information can be lost when internal mixtures are assumed. Herein, we show that during the Southern Oxidant and Aerosol Study (SOAS) in Centreville, Alabama, at a rural, forested 20 location, that aerosols frequently are not purely internally mixed, even in the accumulation mode (0.2-1.0 µm). A range of aerosol sources and mixing states were obtained using computer controlled scanning electron microscopy with energy dispersive X-ray spectroscopy (CCSEM-EDX) and scanning transmission X-ray microscopy-near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). Particles that were dominated by SOA and inorganic salts were the majority of particles by 25 number fraction from 0.2-5 microns with an average of 78% SOA in the accumulation mode. However, during certain periods contributions by sea spray aerosol (SSA) and mineral dust were significant to accumulation (22 % SSA and 26 % dust) and coarse mode number concentrations (38 % SSA and 63% dust). The fraction of particles containing key elements (Na, Mg, K, Ca, and Fe) were determined as a Atmos. Chem. Phys. Discuss., https://doi

Joint Impacts of Acidity and Viscosity on the Formation of Secondary Organic Aerosol from Isoprene Epoxydiols (IEPOX) in Phase Separated Particles

“…Raw data was processed using SPIP 6.2.6 software (Image Metrology, Hørsholm, Denmark) to measure particle height and radius. 58 Scanning electron microscopy (SEM) images were also obtained by examining particles using a FEI Helios 650 Nanolab-Dualbeam electron microscope equipped with a high angle annular dark field (HAADF) detector operated at an accelerating voltage of 10.0 kV, a current of 0.80 nA, and pressures ranging from 10 −3 to 10 −5 Pa.…”

α-Pinene-Derived organic coatings on acidic sulfate aerosol impacts secondary organic aerosol formation from isoprene in a box model

“…While laboratory experiments of IEPOX uptake are often performed using pure inorganic seed, one critical assumption invoked in the CMAQ model is that the aerosol with which IEPOX reacts consists of one homogeneous, internally mixed phase consisting of all organic and inorganic particulate components with no diffusion limitations. In the polluted boundary layer, it is known that acidic sulfate particles rarely exist in pure form (Hatch et al, 2011) and in the southeast US sulfate is almost always mixed with organic material at the individual particle level (Bondy et al, 2018a). Further, these particles may not be homogeneously mixed, and thus, have both diffusion limitations and reduced solubility (Craig et al, 2017;Hatch et al, 2011).…”