AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Quantitative and Time-Resolved Nanoparticle Composition Measurements during New Particle Formation
BRYAN R. BZDEK, Andrew Horan, M. Ross Pennington, Joseph DePalma, Murray Johnston, University of Delaware
Abstract Number: 40 Working Group: Remote and Regional Atmospheric Aerosols
Abstract The elemental composition of 20 nm diameter nanoparticles during new particle formation (NPF) days was measured quantitatively and with high time resolution in a rural/coastal environment with the Nano Aerosol Mass Spectrometer (NAMS). Nanoparticle chemical composition was dynamic during NPF days, and changes in composition did not necessarily correlate with changes in aerosol mass or number concentration. During NPF, nanoparticle composition shifts towards a more inorganic composition. Relative to previous measurements during NPF with NAMS, in this study we identify time-dependent chemical composition changes that are related to different stages of NPF. The particle phase sulfur mole fraction during NPF is quantitatively explained by condensation of sulfuric acid. This is a remarkable observation as it validates existing models describing the sulfuric acid contribution to NPF and it demonstrates the importance of developing models to explain satisfactorily incorporation of other species (e.g. nitrogen-containing and carbonaceous matter) into growing nanoparticles. Nitrogen is shown to exist in excess of that required to neutralize sulfuric acid, indicating a substantial, additional nitrogen-based growth process. Carbonaceous matter is the most abundant component of the growing nanoparticles, although it is the inorganic components that are preferentially enhanced. The results will be compared to observations made by NAMS during NPF in other environments. Although certain aspects (such as the contribution of sulfuric acid to nanoparticle growth) appear to be general characteristics of NPF, other aspects (such as the identity of certain growth species) may be relevant only in certain environments.