AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Silicon is a Nearly Ubiquitous Component of Ambient Nanoparticles
BRYAN R. BZDEK, M. Ross Pennington, Andrew J. Horan, Christopher A. Zordan, Murray Johnston, University of Delaware
Abstract Number: 208 Working Group: Urban Aerosols
Abstract This work presents quantitative elemental composition measurements of individual 20-25 nm atmospheric nanoparticles using the Nano Aerosol Mass Spectrometer. Measurements were conducted in urban (Wilmington, Delaware), suburban (Pasadena, California), rural (Lewes, Delaware), and remote (Hyytiälä, Finland) environments. The nonmetal silicon was found to be present in a low but substantial abundance in a surprisingly large fraction of the nanoparticles measured in environments impacted by humans. For example, more than 48% of the nanoparticles studied during a summertime campaign in Lewes, DE, contained Si with an abundance greater than 1% elemental mole fraction. A campaign in Pasadena, CA, found that more than 40% of the nanoparticles studied contain Si > 1% elemental mole fraction. On the other hand, nanoparticles analyzed in the remote boreal forest contained barely any Si. These observations suggest that nanoparticulate Si tends to be observed more frequently in impacted (rather than remote) environments. Diurnal trends indicate that Si is more abundant during the daytime, suggesting photochemical formation of low-volatility Si-containing compounds from higher volatility precursors. Measurements made in the same location during different seasons show substantial seasonal dependencies on Si content. Combined with meteorological data, these observations suggest local (rather than regional) sources for the Si. In summary, these observations indicate nearly ubiquitous, local sources of Si in environments impacted by human activity. By making assumptions about the molecular species contributing to nanoparticulate Si (e.g. assigning Si to SiO2 or various siloxanes), the atmospheric burdens of these species can reach several tens of ng/m3. These observations suggest a more refined understanding of the sources, reaction pathways, and sinks of organosilicon compounds in the atmosphere is required.