AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Difference in Particle Formation at a Mountain-top Location in Colorado during the Spring and Summer: Modeling and Comparison with Observations
FANGQUN YU, Anna Gannet Hallar, University at Albany
Abstract Number: 332 Working Group: Advances in the Physics and Chemistry of New Particle Formation and Growth
Abstract New particle formation (NPF) is a major source of atmospheric particles with important climatic and environmental impacts, and a firm understanding of dominant mechanism(s) of NPF in the atmosphere remains to be achieved. NPF has been observed frequently at Storm Peak Laboratory (SPL), a high elevation mountain-top observatory in Colorado. Analysis of recently available continuous measurements of condensation nuclei larger than 10 nm as well as particle size distributions reveals significant difference in the NPF during the Spring and Summer at SPL. Model simulations based on a global chemical transport model (GEOS-Chem) coupled with a size-resolved (sectional) advanced particle microphysics (APM) model are used to interpret in-depth the nucleation phenomena at SPL, focusing in this study on one Spring month (March 2012) and one Summer month (July 2012). The model, with nucleation rates calculated based on the ion-mediated nucleation mechanism, captures well the observed persistent daily nucleation events in March (almost every day) and very few NPF in July. While UV-B flux is ~ 50% higher in July, OH concentrations of the two months are comparable, probably as a result of much larger concentration of volatile organic carbons (VOCs) in the summer. Based on the model simulations, the monthly mean sulfuric acid gas concentration in July is a factor of ~ 2.5 lower than that in March but the concentration of condensable (low volatile highly oxidized) secondary organic gases is a factor of 4 higher in July. The high nucleation rates in March and the lack of nucleation in July indicate that sulfuric acid plays a much more important role in the initial nucleation process although organics compounds contribute significantly to the particle growth. Other factors contributing to the large difference in NPF at SPL during the Spring and Summer will also be discussed.