Filters

2015 - 20192

More filters

2019 - 20202
Reset filters

Settings

search.filters.applied.f.access: openAccess × Author: Ma, N. × Author: Wiedensohler, A. × End date: 2019 × Start date: 2010 × Has files: Yes × Subject: hygroscopicity × Subject: supersaturation ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Scanning supersaturation condensation particle counter applied as a nano-CCN counter for size-resolved analysis of the hygroscopicity and chemical composition of nanoparticles
    (München : European Geopyhsical Union, 2015) Wang, Z.; Su, H.; Wang, X.; Ma, N.; Wiedensohler, A.; Pöschl, U.; Cheng, Y.
    Knowledge about the chemical composition of aerosol particles is essential to understand their formation and evolution in the atmosphere. Due to analytical limitations, however, relatively little information is available for sub-10 nm particles. We present the design of a nano-cloud condensation nuclei counter (nano-CCNC) for measuring size-resolved hygroscopicity and inferring chemical composition of sub-10 nm aerosol particles. We extend the use of counting efficiency spectra from a water-based condensation particle counter (CPC) and link it to the analysis of CCN activation spectra, which provides a theoretical basis for the application of a scanning supersaturation CPC (SS-CPC) as a nano-CCNC. 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 κ and organic mass fraction is also found for sucrose-ammonium sulfate mixtures. The design is not limited to the water CPC, but also applies to CPCs with other working fluids (e.g. butanol, perfluorotributylamine). We suggest that a combination of SS-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.
  • Thumbnail Image
    Item
    Characterization of aerosol properties at Cyprus, focusing on cloud condensation nuclei and ice-nucleating particles
    (Göttingen : Copernicus GmbH, 2019) Gong, X.; Wex, H.; Müller, T.; Wiedensohler, A.; Höhler, K.; Kandler, K.; Ma, N.; Dietel, B.; Schiebel, T.; Möhler, O.; Stratmann, F.
    As part of the A-LIFE (Absorbing aerosol layers in a changing climate: aging, LIFEtime and dynamics) campaign, ground-based measurements were carried out in Paphos, Cyprus, to characterize the abundance, properties, and sources of aerosol particles in general and cloud condensation nuclei (CCN) and ice-nucleating particles (INP) in particular. New particle formation (NPF) events with subsequent growth of the particles into the CCN size range were observed. Aitken mode particles featured k values of 0.21 to 0.29, indicating the presence of organic materials. Accumulation mode particles featured a higher hygroscopicity parameter, with a median k value of 0.57, suggesting the presence of sulfate and maybe sea salt particles mixed with organic carbon. A clear downward trend of k with increasing supersaturation and decreasing dcrit was found. Super-micron particles originated mainly from sea-spray aerosol (SSA) and partly from mineral dust. INP concentrations (NINP) were measured in the temperature range from-6:5 to-26:5 °C, using two freezing array-type instruments. NINP at a particular temperature span around 1 order of magnitude below-20 °C and about 2 orders of magnitude at warmer temperatures (T >-18 °C). Few samples showed elevated concentrations at temperatures >-15 °C, which suggests a significant contribution of biological particles to the INP population, which possibly could originate from Cyprus. Both measured temperature spectra and NINP probability density functions (PDFs) indicate that the observed INP (ice active in the temperature range between-15 and-20 °C) mainly originate from long-range transport. There was no correlation between NINP and particle number concentration in the size range> 500 nm (N>500 nm). Parameterizations based on N>500 nm were found to overestimate NINP by about 1 to 2 orders of magnitude. There was also no correlation between NINP and particle surface area concentration. The ice active surface site density (ns) for the polluted aerosol encountered in the eastern Mediterranean in this study is about 1 to 3 orders of magnitude lower than the ns found for dust aerosol particles in previous studies. This suggests that observed NINP PDFs such as those derived here could be a better choice for modeling NINP if the aerosol particle composition is unknown or uncertain.