Ice-Nucleating Particle Spectra Relevant for Mixed-Phase Clouds from the Tropics to the Arctic Measured from a Research Aircraft

Ice-Nucleating Particles (INPs) are the subset of aerosol particles which can trigger ice-nucleation of the cloud droplets at higher temperatures than required for homogeneous nucleation. This results in a series of microphysical process which can deplete liquid water in mixed-phased clouds and dramatically alter their radiative properties. The ice-nucleating ability of aerosol particles strongly depends on its composition, which makes the INP concentrations vary considerably across different locations. Understanding correctly the sources and transport of INPs is particularly important since the representation of INPs in some models can affect the flux of radiation, which has a significant effect on the earth’s temperature (Lohmann and Diehl, 2006; Tan et al., 2016; Vergara-Temprado et al., 2018). Hence, we need to improve our understanding of the global distribution of INPs.

Here we use a filter based technique to measure atmospheric INPs on top of filters which have been collected on board of the BAe-146 FAAM aircraft in a range of contrasting environments, from the tropics to the Arctic. INP measurements are carried out in parallel with a compositional analysis using Scanning Electron Microscopy (SEM), in order to obtain the size-segregated composition of the atmospheric aerosol particles (Sanchez-Marroquin et al., 2019). This double analysis has been applied in three field campaigns in very contrasting locations: UK, Iceland and Alaska (we also compare with a published dataset in Cape Verde where we used the same technique (Price et al., 2018)).

We clearly show that the INP concentration spectra in the different environments are very different (scattering more than 12 ^oC at a given concentration), but that there is also a great deal of variability at single locations (Fig. 1). Aerosol samples dominated by Saharan dust with large concentrations of INPs were collected in Cape Verde (Price et al., 2018). The samples collected in the UK were very heterogeneous in composition, and the INP concentrations were not as high as in Cape Verde at lower temperatures, but at above about -15°C some of the spectra have higher concentrations. This is consistent with a local, probably biogenic INP source which has been inferred from ground based measurements (O'Sullivan et al., 2018). Icelandic samples were dominated by the presence of local re-suspended volcanic material, which we find is an effective ice-nucleator, with the potential to contribute significantly to INP population at mid- to high-latitudes (Sanchez-Marroquin et al., In prep). Both the aerosol and INP concentrations in Alaska were very low. Our results also show that most of the measured INP concentrations can be explained based on the aerosol surface area of the sample, and particularly the presence of mineral dust.

This study helps to understand the sources and distributions of INPs at different locations, showing its high spatial variability which presumably leads to variability in ice and supercooled water content in clouds around the world. This is particularly relevant since there are very few INP measurements around the globe and we are yet to quantify all INP sources.

References

Lohmann, U. and Diehl, K. 2006. Sensitivity Studies of the Importance of Dust Ice Nuclei for the Indirect Aerosol Effect on Stratiform Mixed-Phase Clouds. Journal of the Atmospheric Sciences. 63(3), pp.968-982.

O'Sullivan, D., Adams, M.P., Tarn, M.D., Harrison, A.D., Vergara-Temprado, J., Porter, G.C.E., Holden, M.A., Sanchez-Marroquin, A., Carotenuto, F., Whale, T.F., McQuaid, J.B., Walshaw, R., Hedges, D.H.P., Burke, I.T., Cui, Z. and Murray, B.J. 2018. Contributions of biogenic material to the atmospheric ice-nucleating particle population in North Western Europe. Sci Rep. 8(1), p13821.

Petters, M.D. and Wright, T.P. 2015. Revisiting ice nucleation from precipitation samples. Geophysical Research Letters. 42(20), pp.8758-8766.

Price, H.C., Baustian, K.J., McQuaid, J.B., Blyth, A., Bower, K.N., Choularton, T., Cotton, R.J., Cui, Z., Field, P.R., Gallagher, M., Hawker, R., Merrington, A., Miltenberger, A., Neely Iii, R.R., Parker, S.T., Rosenberg, P.D., Taylor, J.W., Trembath, J., Vergara-Temprado, J., Whale, T.F., Wilson, T.W., Young, G. and Murray, B.J. 2018. Atmospheric Ice-Nucleating Particles in the Dusty Tropical Atlantic. Journal of Geophysical Research: Atmospheres. 123(4), pp.2175-2193.

Sanchez-Marroquin, A., Hedges, D.H.P., Hiscock, M., Parker, S.T., Rosenberg, P.D., Trembath, J., Walshaw, R., Burke, I.T., McQuaid, J.B. and Murray, B.J. 2019. Characterisation of the filter inlet system on the BAE-146 research aircraft and its use for size resolved aerosol composition measurements. Atmospheric Measurement Techniques Discussions. pp.1-35.

Tan, I., Storelvmo, T. and Zelinka, M.D. 2016. Observational constraints on mixed-phase clouds imply higher climate sensitivity. Science. 352(6282), pp.224-227.

Vergara-Temprado, J., Miltenberger, A.K., Furtado, K., Grosvenor, D.P., Shipway, B.J., Hill, A.A., Wilkinson, J.M., Field, P.R., Murray, B.J. and Carslaw, K.S. 2018. Strong control of Southern Ocean cloud reflectivity by ice-nucleating particles. Proc Natl Acad Sci U S A. 115(11), pp.2687-2692.

CAPTION: Figure 1. INP concentration measurements at different locations. Data has been compared with the range of typical INP concentrations at various locations and sessions from (Petters and Wright, 2015). (*) All the Cape Verde data was obtained by (Price et al., 2018). Circles represent data significantly above the limit of detection while crosses represent upper limits.