Articles | Volume 15, issue 1
Atmos. Chem. Phys., 15, 393–409, 2015
Atmos. Chem. Phys., 15, 393–409, 2015

Research article 13 Jan 2015

Research article | 13 Jan 2015

Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

P. J. DeMott1, A. J. Prenni1,*, G. R. McMeeking2, R. C. Sullivan3, M. D. Petters4, Y. Tobo1,**, M. Niemand5, O. Möhler5, J. R. Snider6, Z. Wang6, and S. M. Kreidenweis1 P. J. DeMott et al.
  • 1Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523-1371, USA
  • 2Droplet Measurement Technologies, Boulder, CO, USA
  • 3Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA
  • 4Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA
  • 5Institute for Meteorology and Climate Research – Atmospheric Aerosol Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 6Department of Atmospheric Sciences, University of Wyoming, Laramie, WY, USA
  • *now at: Air Resources Division, National Park Service, Denver, CO, USA
  • **now at: National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan

Abstract. Data from both laboratory studies and atmospheric measurements are used to develop an empirical parameterization for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RHw) are taken as a measure of the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterization developed follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 μm diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A calibration factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RHw of 105% vs. maximum fractions active at higher RHw. Instrumental factors that affect activation behavior vs. RHw in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this calibration factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization, including calibration correction, to predictions of the immersion freezing surface active site density parameterization for mineral dust particles, developed separately from AIDA experimental data alone, shows excellent agreement for data collected in a descent through a Saharan aerosol layer. These studies support the utility of laboratory measurements to obtain atmospherically relevant data on the ice nucleation properties of dust and other particle types, and suggest the suitability of considering all mineral dust as a single type of ice nucleating particle as a useful first-order approximation in numerical modeling investigations.

Short summary
Laboratory and field data are used together to develop an empirical relation between the concentrations of mineral dust particles at sizes above 0.5 microns, approximated as a single compositional type, and ice nucleating particle concentrations measured versus temperature. This should be useful in global modeling of ice cloud formation. The utility of laboratory data for parameterization development is reinforced, and the need for careful interpretation of ice nucleation data is emphasized.
Final-revised paper