Aerosol & Air Quality

Research Group Dr. Yafang Cheng

Key Topics

    Thermodynamic and kinetics of nanoparticles
    Multiphase chemistry in haze, fog and cloud
    Black carbon and its climate effects (project leader: Dr. Nan Ma)

Methods

    Classical thermodynamic theories
    Molecular dynamic simulations
    Regional and global atmospheric model simulations
    Innovative development and application of instrumentation: nano-H/V-TDMA, nano-CCNC, size-resolved single- particle fluorescence spectrometer, Atomic Force Microscopy, etc.
    Long-term aircraft measurements

Research highlight:

New 3D phase diagram: Cheng et al. Size dependence of phase transitions in aerosol nanoparticles. Nature Communications, 2015 http://www.nature.com/ncomms/2015/150114/ncomms6923/full/ncomms6923.html

Phase transitions of nanoparticles are of fundamental importance in atmospheric sciences, but current understanding is insufficient to explain observations at the nano-scale. In particular, discrepancies exist between observations and model predictions of deliquescence and efflorescence transitions and the hygroscopic growth of salt nanoparticles. Here we show that these discrepancies can be resolved by consideration of particle size effects with consistent thermodynamic data. We present a new method for the determination of water and solute activities and interfacial energies in highly supersaturated aqueous solution droplets (Differential Köhler Analysis). Our analysis reveals that particle size can strongly alter the characteristic concentration of phase separation in mixed systems, resembling the influence of temperature. Owing to similar effects, atmospheric secondary organic aerosol particles at room temperature are expected to be always liquid at diameters below ~20 nm. We thus propose and demonstrate that particle size should be included as an additional dimension in the equilibrium phase diagram of aerosol nanoparticles.

Hot paper (top 0.1%) in Web of Science: Zheng, G. J. et al. Exploring the severe winter haze in Beijing: the impact of synoptic weather, regional transport and heterogeneous reactions. Atmos. Chem. Phys. 15, 2969-2983, doi:10.5194/acp-15-2969-2015 (2015).

Launch of the CARIBIC Aircraft Observation of Black Carbon (CAOBC) project: The black carbon is the second most important anthropogenic climate-warming agent after carbon dioxide. Despite of its importance, the estimated climate forcing of black carbon is subject to large uncertainties. In this project, we perform black carbon measurements with a single particle soot photometer (SP2) installed in the CARIBIC container onboard of a Lufthansa passenger aircraft. The figure below shows the areas with data from previous flight routes (red dots).

Recent research activity:

15.06.2016 Invited Talk at 'CLOUD-TRAIN' workshop, Frankfurt (Yafang Cheng, Hang Su, T. Koop, E. Mikhailov, U. Poeschl, Size dependence of phase transition in aerosol nanoparticles, CLOUD-TRAIN workshop, Frankfurt, 15 June 2016)

Job opportunities:

Postdoctoral and Ph.D positions are open in my group. We are particular interested in experienced posdoc with MD simulation skill to study the nano-size effect and interface phenomena. Please send your CV, a short research statement, and a list of 2-3 references to Dr. Yafang Cheng (yafang.cheng@mpic.de).