PNNL

Abstract

The chemical composition of respiratory particles is of interest because the viability of any viruses and bacteria in the particles has been shown to depend on this factor. Using computer controlled scanning electron microscopy/energy dispersive x-ray spectroscopy (CCSEM/EDX), we analyzed the size-resolved chemical composition of >5000 respiratory particles collected from two healthy human subjects, quantitatively at nanometer-scale spatial resolution. Nearly all the desiccated particles were smaller than 1 ?m, and the mode of the size distribution was ~0.1 ?m. Particles were heterogeneous in composition, with some particles richer in carbon and others in sodium, while some particles contained both elements. Based on the particles’ elemental composition, we classified them into five categories: 48-56% were organic, 40-50% were Na-rich salt, 0.3-0.5% were P-rich salt, 0.1-0.8% were K-rich salt, and 1-2.5% were mixed salt. Finally, we found that smaller particles are enriched in organic material while larger ones are dominated by Na-rich salt. This study advances our understanding of the chemical microenvironment to which pathogens are exposed while transmitting between hosts.