INVITED ABSTRACT
Mixing State and Compositional Effects on CCN Activity and Droplet Growth Kinetics of Size-Resolved CCN in an Urban Environment

LUZ TERESA PADRO (1), Richard H. Moore (1), Xialou Zhang (1), Neeraj Rastogi (1,2), Jessie Creamean (3), Lindsay Hatch (3), Andrew Ault (3), Kimberly A. Prather (3), Rodney J. Weber (1), and Athanasios Nenes (1)

(1) Georgia Institute of Technology, (2) University of Toronto, (3) University of California San Diego

     Abstract Number: 748
     Last modified: May 14, 2010

Abstract
The effect of aerosol composition (especially from organic species) on the cloud droplet formation process is highly variable and is currently the largest source of uncertainty in aerosol-cloud-climate interaction studies. These uncertainties can be largely constrained by in-situ size-resolved Cloud Condensation Nuclei (CCN) measurements of atmospheric aerosols. We present a complete characterization of aerosols and CCN sampled during the 2008 AMIGAS campaign which took place in Atlanta, GA. The city of Atlanta offers a unique environment were the interactions between biogenic and anthropogenic emissions contribute to the formation and transformation of particulate matter. CCN concentrations were measured using the Streamwise Thermal Gradient CCN Chamber (STGC1), size distributions from a Scanning Mobility Particle Sizer, and chemical composition from two Particle-Into-Liquid-Samplers, one coupled to an ion chromatograph and the other to a Total Organic Carbon Analyzer, and an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS). Size-resolved CCN data was collected using the Scanning Mobility CCN Analysis (SMCA2) method, where the monodisperse ambient aerosol from a Differential Mobility Analyzer (operated in scanning mode) is concurrently introduced into a STGC and a Condensation Particle Counter. Inversion of the concentration timeseries from both instruments yields the activation ratio (i.e., fraction of particles that become CCN) and size of activated droplets, as a function of dry mobility diameter and supersaturation. The daily trend of the CCN activity and droplet growth kinetic of the size-resolved CCN are presented and compared to chemical composition measurements. Furthermore, the measured ATOFMS mixing state is compared to the CCN mixing state derived from our measurements. Inferences about the impact of photochemistry and mixing on CCN activity, hygroscopic water uptake, and droplet growth kinetics are carried out. Finally we quantify the predictive uncertainty associated with simplifying compositional assumptions (e.g., size-invariant composition, organic insoluble/soluble with constant hygroscopicity) when used to predict CCN concentrations.