Measurements of cloud condensation nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals 1School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
15 Apr 2011
2School of Earth & Atmospheric Sciences, Georgia Institute of Technology Atlanta, GA, 30332, USA
Received: 28 November 2010 – Published in Atmos. Chem. Phys. Discuss.: 21 December 2010 Abstract. This study reports laboratory measurements of cloud condensation nuclei
(CCN) activity and droplet activation kinetics of aerosols dry generated
from clays, calcite, quartz, and desert soil samples from Northern Africa,
East Asia/China, and Northern America. Based on the observed dependence of
critical supersaturation, sc, with particle dry diameter, Ddry, we
found that FHH (Frenkel, Halsey and Hill) adsorption activation theory is a
far more suitable framework for describing fresh dust CCN activity than
Köhler theory. One set of FHH parameters (AFHH ∼ 2.25 ± 0.75, BFHH ∼ 1.20 ± 0.10) can adequately reproduce the
measured CCN activity for all species considered, and also explains the
large range of hygroscopicities reported in the literature. Based on a
threshold droplet growth analysis, mineral dust aerosols were found to
display retarded activation kinetics compared to ammonium sulfate.
Comprehensive simulations of mineral dust activation and growth in the CCN
instrument suggest that this retardation is equivalent to a reduction of the
water vapor uptake coefficient (relative to that for calibration ammonium
sulfate aerosol) by 30–80%. These results suggest that dust particles
do not require deliquescent material to act as CCN in the atmosphere.
Revised: 01 April 2011 – Accepted: 01 April 2011 – Published: 15 April 2011
Citation: Kumar, P., Sokolik, I. N., and Nenes, A.: Measurements of cloud condensation nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals, Atmos. Chem. Phys., 11, 3527-3541, doi:10.5194/acp-11-3527-2011, 2011.