AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Nanoparticle Chemical Composition During New Particle Formation
BRYAN R. BZDEK, M. Ross Pennington, Murray Johnston, University of Delaware
Abstract Number: 410 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract The Nano Aerosol Mass Spectrometer (NAMS) permits quantitative measurement of the atomic composition of individual nanoparticles between 7 and 30 nm diameter. NAMS was deployed to urban, rural/coastal, and remote environments in order to determine the composition of 15-21 nm mobility diameter nanoparticles during new particle formation (NPF) events. In all three environments, only small changes in nanoparticle atomic composition were observed during NPF relative to composition before and after the events. These changes indicated a shift towards increased inorganic nanoparticle content during NPF (more nitrogen and sulfur, less carbon). Nonetheless, nanoparticles in this size range still contained a significant organic component, characterized by a high carbon content. For each environment, chemical composition changes did not correlate with changes in the event growth rate, suggesting (1) that a consistent source exists for all events at a given site and (2) that the driving forces affecting particle growth are physical (i.e. solar radiation, mixing, meteorology) rather than chemical and impact all chemical constituents of the particle in a roughly similar manner. Nonetheless, chemical composition is found to depend on parameters such as temperature or snow pack. NAMS-measured elemental sulfur content can be related quantitatively to ambient gas-phase sulfuric acid during NPF through the gamma parameter. Agreement between measured particulate sulfur and gas-phase sulfuric acid concentrations indicates that the assumption of collision-limited condensational growth of sulfuric acid is suitable for 10-20 nm diameter particles. Current work focuses on the contributions of organic matter and nitrogen-containing species such as base molecules (amines, ammonia) to particle growth.