1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Woodhouse
Lane, Leeds, LS2 9JT, UK
2College of Life and Environmental Sciences, University of Exeter, Penryn, TR10 9EZ, UK
3Department of System Biology, Harvard University, Harvard Medical School, Boston, USA
4Department of Chemistry, University of British Columbia, Vancouver, BC, V6T1Z1, Canada
5Pacific Northwest National Laboratory, Atmospheric Sciences and Global Change Division, P.O. Box 999 MS K-24, Richland, WA 99352, USA
6School of Physics and Centre for Climate and Air Pollution Studies, Ryan Institute, National University of Ireland Galway, Galway, Ireland
7Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523-1371, USA
8Italian National Research Council (CNR), Institute of Environmental Sciences and Climate (ISAC), via P. Gobetti 101, 40129 Bologna, Italy
Received: 14 Sep 2016 – Discussion started: 21 Sep 2016
Abstract. Ice-nucleating particles (INPs) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. The atmospheric INP concentration changes by orders of magnitude from terrestrial to marine environments, which typically contain much lower concentrations. Many modelling studies use parameterizations for heterogeneous ice nucleation and cloud ice processes that do not account for this difference because they were developed based on INP measurements made predominantly in terrestrial environments without considering the aerosol composition. Errors in the assumed INP concentration will influence the simulated amount of ice in mixed-phase clouds, leading to errors in top-of-atmosphere radiative flux and ultimately the climate sensitivity of the model. Here we develop a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Underestimation of INP concentrations in some terrestrial locations may be due to the neglect of INPs from other terrestrial sources. Our model indicates that, on a monthly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important over remote oceans and they dominate over the Southern Ocean. However, day-to-day variability is important. Because desert dust aerosol tends to be sporadic, marine organic aerosols dominate the INP population on many days per month over much of the mid- and high-latitude Northern Hemisphere. This study advances our understanding of which aerosol species need to be included in order to adequately describe the global and regional distribution of INPs in models, which will guide ice nucleation researchers on where to focus future laboratory and field work.
Revised: 16 Feb 2017 – Accepted: 01 Mar 2017 – Published: 15 Mar 2017
Vergara-Temprado, J., Murray, B. J., Wilson, T. W., O'Sullivan, D., Browse, J., Pringle, K. J., Ardon-Dryer, K., Bertram, A. K., Burrows, S. M., Ceburnis, D., DeMott, P. J., Mason, R. H., O'Dowd, C. D., Rinaldi, M., and Carslaw, K. S.: Contribution of feldspar and marine organic aerosols to global ice nucleating particle concentrations, Atmos. Chem. Phys., 17, 3637-3658, doi:10.5194/acp-17-3637-2017, 2017.