Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

C Chou,O Stetzer,Z A Kanji,U Lohmann,E Weingartner,Z Jurányi

doi:10.5194/acp-11-4725-2011

C Chou, O Stetzer + Show 4 more

Open Access

https://doi.org/10.5194/acp-11-4725-2011

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Abstract

Abstract. The new portable ice nucleation chamber (PINC) developed by the Institute for Atmospheric and Climate Sciences of ETH Zurich was operated during two measurement campaigns at the high alpine research station Jungfraujoch situated at 3580 m a.s.l, in March and June 2009. During this time of the year, a high probability of Saharan dust events (SDE) at the Jungfraujoch has been observed. We used an impactor with a cutoff size of 1 μm aerodynamic diameter and operated the system at −31 °C and relative humidities of 127 % and 91 % with respect to ice and water, respectively. Investigation of the ambient number concentration of ice nuclei (IN) in the deposition nucleation mode and during a SDE in the free troposphere is reported. The results discussed in this paper are the first continuous IN measurements over a period of several days at the Jungfraujoch. The average IN concentration found during the campaign in March was 8 particles per liter whereas during the campaign in June, the average number concentration was higher up to 14 particles per liter. Two SDEs were detected on 15 and 16 June 2009. Our measurements show that the SDEs had IN number concentration up to several hundreds per liter. We found the best correlation between the number concentration of the larger particle fraction measured by an optical particle counter and the IN number concentration during a Saharan dust event. This correlation factor is higher for particles larger than 0.5 μm meaning that a higher concentration of larger particles induced higher IN number concentration. No correlation could be found between the black carbon mass concentration and the variations in IN number concentration.

Highlights

Atmospheric aerosols contribute to the largest uncertainty in the global radiative forcing since pre-industrial times (Forster et al, 2007)
At higher temperatures the formation of ice in clouds is triggered by heterogeneous nucleation which is divided into four sub-processes: Immersion, condensation, contact and deposition nucleation (Vali, 1985)
The main objective of this study is to focus on the deposition nucleation mode, so it is crucial that the particles sampled are dry

Summary

Introduction

Atmospheric aerosols contribute to the largest uncertainty in the global radiative forcing since pre-industrial times (Forster et al, 2007). Many laboratory studies as for example Mason and Maybank (1958); Isono et al (1959); Roberts and Hallett (1968); Schaller and Fukuta (1979); Pruppacher and Klett (1997); DeMott (2002); Zuberi et al (2002); Archuleta et al (2005); Mangold et al (2005); Kanji and Abbatt (2006); Knopf and Koop (2006); Mohler et al (2006); Marcolli et al (2007); Eastwood et al (2008); Welti et al (2009); Kulkarni and Dobbie (2010) have shown that mineral dust is a good ice nucleus (IN) in both immersion and deposition nucleation mode and usually initiate nucleation at rather high temperatures and low relative humidities This statement is supported by field studies (DeMott et al, 2003b; Richardson et al, 2007; Klein et al, 2010) where high concentrations of mineral dust led to a significant increase in the ice crystal number concentration. Previous studies by Vali et al (1976); Published by Copernicus Publications on behalf of the European Geosciences Union

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