AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Scanning Supersaturation CPC Applied as a Nano-CCN Counter for Size-resolved Analysis of the Hygroscopicity and Chemical Composition of Nanoparticles
Zhibin Wang, HANG SU, Xin Wang, Nan Ma, Alfred Wiedensohler, Ulrich Poeschl, Yafang Cheng, Max Planck Institute for Chemistry
Abstract Number: 142 Working Group: Aerosol Physics
Abstract Knowledge on the chemical composition and hygroscopicity is essential for understanding the formation and evolution of atmospheric aerosol particles. However, relatively little information is available for nanoparticles due to experimental difficulties. We present the design of a nano-cloud condensation nuclei (nano-CCN) counter for the purpose of measuring size-resolved hygroscopicity and interpreting chemical compositions of sub-10 nm particles. Advanced than the previous study, here we extend the use of counting efficiency spectra of condensation particle counter (CPC) and link it to the analysis of CCN activation spectra, which provides a theoretical basis for the modification of CPC to a nano-CCN counter. Since CCN hygroscopicity has been demonstrated as an effective parameter reflecting organic and inorganic mass fractions, the nano-CCN counter may thus provide size-resolved information on the chemical composition of sub-10 nm nanoparticles.
By using calibration aerosols, we show the importance of using activation fraction of aerosol samples to calibrate supersaturation distribution inside CPC and its use in further retrieval of aerosol hygroscopicities. Measurement procedures and data analysis methods are demonstrated through laboratory experiments with monodisperse particles of diameter down to 2.5 nm, where sodium chloride, ammonium sulfate, sucrose and tungsten oxide can be easily discriminated by different characteristic supersaturations of water droplet formation. A near-linear relationship between hygroscopicity parameter kappa and organic mass fraction is also found for sucrose-ammonium sulfate mixtures. Though named nano-CCN counter, the design is not limited to the water-CPC, but also applies to CPCs of other working fluid. We suggest that a combination of scanning supersaturation CPCs with multiple working fluids may provide further insight into the chemical composition of nanoparticles and the role of organic and inorganic compounds in the initial steps of atmospheric new particle formation and growth.