Size-resolved measurements of ice-nucleating particles at six locations in North America and one in Europe

Ryan H Mason ,C Chou,J A Huffman,M Brintnell,W M Lassar,A M Macdonald,T C J Hill,W R Leaitch,C L Schiller,D Toom-Sauntry,Kaitlyn J Suski ,Victoria E Irish ,Ryan Dickie ,Andrew W.g Platt ,Pablo Elizondo ,Jonathan P D Abbatt ,Roland Sarda‐Estève ,Paul J Demott ,Roger Wong ,Kyle M Pierce ,Meng Si ,Mike Elsasser ,Allan K Bertram

doi:10.5194/acp-16-1637-2016

Abstract

Abstract. Detailed information on the size of ice-nucleating particles (INPs) may be useful in source identification, modeling their transport in the atmosphere to improve climate predictions, and determining how effectively or ineffectively instrumentation used for quantifying INPs in the atmosphere captures the full INP population. In this study we report immersion-mode INP number concentrations as a function of size at six ground sites in North America and one in Europe using the micro-orifice uniform-deposit impactor droplet freezing technique (MOUDI-DFT), which combines particle size-segregation by inertial impaction and a microscope-based immersion freezing apparatus. The lowest INP number concentrations were observed at Arctic and alpine locations and the highest at suburban and agricultural locations, consistent with previous studies of INP concentrations in similar environments. We found that 91 ± 9, 79 ± 17, and 63 ± 21 % of INPs had an aerodynamic diameter > 1 µm at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. In addition, 62 ± 20, 55 ± 18, and 42 ± 17 % of INPs were in the coarse mode (> 2.5 µm) at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. These results are consistent with six out of the nine studies in the literature that have focused on the size distribution of INPs in the atmosphere. Taken together, these findings strongly suggest that supermicron and coarse-mode aerosol particles are a significant component of the INP population in many different ground-level environments. Further size-resolved studies of INPs as a function of altitude are required since the size distribution of INPs may be different at high altitudes due to size-dependent removal processes of atmospheric particles.

Highlights

Ice-nucleating particles (INPs) are a unique class of aerosol particles that catalyze ice formation under atmospheric conditions
High-elevation sites can receive large quantities of dust, which can act as efficient INPs at lower temperatures (Chou et al, 2011), but this was unlikely during our measurement period based on the low INP number concentrations
INP number concentrations in the immersion mode as a function of size and droplet freezing temperature were determined at six locations across North America and one in Europe

Summary

Introduction

Ice-nucleating particles (INPs) are a unique class of aerosol particles that catalyze ice formation under atmospheric conditions. A variety of particle types have been identified as INPs, including mineral dust, black carbon, volcanic ash, glassy aerosols, and primary biological particles such as bacteria, fungal spores, and pollen (see reviews by Szyrmer and Zawadzki, 1997; Möhler et al, 2007; Ariya et al, 2009; Després et al, 2012; Hoose and Möhler, 2012; Murray et al, 2012; Yakobi-Hancock et al, 2013). Only a small fraction of aerosol particles nucleate ice (e.g., Rogers et al, 1998), INPs are important since they can lead to changes in the properties and lifetimes of mixed-phase and ice clouds, Published by Copernicus Publications on behalf of the European Geosciences Union. Mason et al.: Size-resolved measurements of ice-nucleating particles affecting climate and precipitation (Baker, 1997; Lohmann and Feichter, 2005; Baker and Peter, 2008; DeMott et al, 2010; Creamean et al, 2013)

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Results

Conclusion