AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Vertically Resolved Concentration and Liquid Water Content of Atmospheric Nanoparticles at the US DOE Southern Great Plains Site
HAIHAN CHEN, Anna Hodshire, John Ortega, James Greenberg, Peter H. McMurry, Annmarie Carlton, Jeffrey R. Pierce, David Hanson, James Smith, University of California, Irvine
Abstract Number: 564 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract Most previous field studies of new particle formation (NPF) have been performed at or near ground level, but some measurements suggest that nucleation can be altitude dependent. Lower temperature and high relative humidity (RH) at higher altitudes can favor nucleation and growth pathways that are not important at ground level. Vertically resolved studies of NPF are thereby needed to better understand the chemical species and mechanisms driving NPF, as well as adequately assess the impacts of NPF on cloud formation and climate. We report measurements of 10-20 nm diameter particle number concentrations from ground level to 1000 m above ground during the 2013 New Particle Formation Study at the Atmospheric Radiation Measurements Southern Great Plains site in Lamont, Oklahoma. The measurements were performed using a tethered balloon carrying two condensation particle counters that were configured for two different particle cut-off diameters. Those observations are compared to data from three scanning mobility particle sizers at the ground level to examine the spatial and temporal profiles of NPF. We observed that 10-20 nm diameter particles were generated at the top region of the boundary layer, and were then rapidly mixed throughout the boundary layer. We estimate liquid water content (LWC) of newly formed particles using ground-based measurements of particle hygroscopicity obtained with a Humidified Tandem Differential Mobility Analyzer and vertically-resolved relative humidity and temperature measured with a Raman Lidar. Our estimates of liquid water content suggest that nanoparticles typically contain up to 50% water by volume in ambient air. The effect of LWC of newly formed particles on particle growth is examined by the MABNAG nanoparticle growth model. The modelling results indicate that the increased liquid water content of nanoparticles at high RH greatly enhances the partitioning of water soluble species like organic acids into ambient nanoparticles.