Hygroscopicity distribution concept for measurement data analysis and modeling of aerosol particle mixing state with regard to hygroscopic growth and CCN activation 1Max Planck Institute for Chemistry, 55020 Mainz, Germany
2Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
Received: 08 December 2009 – Published in Atmos. Chem. Phys. Discuss.: 18 January 2010 Abstract. This paper presents a general concept and mathematical framework of particle
hygroscopicity distribution for the analysis and modeling of aerosol
hygroscopic growth and cloud condensation nucleus (CCN) activity. The
cumulative distribution function of particle hygroscopicity, H(κ, Dd) is defined as the number fraction of particles with a given dry
diameter, Dd, and with an effective hygroscopicity parameter smaller
than the parameter κ. From hygroscopicity tandem differential mobility
analyzer (HTDMA) and size-resolved CCN measurement data, H(κ, Dd) can be derived by solving the κ-Köhler model equation.
Alternatively, H(κ, Dd) can be predicted from measurement or
model data resolving the chemical composition of single particles.
Revised: 03 August 2010 – Accepted: 05 August 2010 – Published: 12 August 2010
A range of model scenarios are used to explain and illustrate the concept,
and exemplary practical applications are shown with HTDMA and CCN measurement
data from polluted megacity and pristine rainforest air. Lognormal
distribution functions are found to be suitable for approximately describing
the hygroscopicity distributions of the investigated atmospheric aerosol
For detailed characterization of aerosol hygroscopicity distributions,
including externally mixed particles of low hygroscopicity such as freshly
emitted soot, we suggest that size-resolved CCN measurements with a wide
range and high resolution of water vapor supersaturation and dry particle
diameter should be combined with comprehensive HTDMA measurements and
size-resolved or single-particle measurements of aerosol chemical
composition, including refractory components. In field and laboratory
experiments, hygroscopicity distribution data from HTDMA and CCN measurements
can complement mixing state information from optical, chemical and
volatility-based techniques. Moreover, we propose and intend to use
hygroscopicity distribution functions in model studies investigating the
influence of aerosol mixing state on the formation of cloud droplets.
Citation: Su, H., Rose, D., Cheng, Y. F., Gunthe, S. S., Massling, A., Stock, M., Wiedensohler, A., Andreae, M. O., and Pöschl, U.: Hygroscopicity distribution concept for measurement data analysis and modeling of aerosol particle mixing state with regard to hygroscopic growth and CCN activation, Atmos. Chem. Phys., 10, 7489-7503, doi:10.5194/acp-10-7489-2010, 2010.