Abstract

Abstract. In this work we describe the Horizontal Ice Nucleation Chamber (HINC) as a new instrument to measure ambient ice-nucleating particle (INP) concentrations for conditions relevant to mixed-phase clouds. Laboratory verification and validation experiments confirm the accuracy of the thermodynamic conditions of temperature (T) and relative humidity (RH) in HINC with uncertainties in T of ±0.4 K and in RH with respect to water (RHw) of ±1.5 %, which translates into an uncertainty in RH with respect to ice (RHi) of ±3.0 % at T > 235 K. For further validation of HINC as a field instrument, two measurement campaigns were conducted in winters 2015 and 2016 at the High Altitude Research Station Jungfraujoch (JFJ; Switzerland, 3580 m a. s. l. ) to sample ambient INPs. During winters 2015 and 2016 the site encountered free-tropospheric conditions 92 and 79 % of the time, respectively. We measured INP concentrations at 242 K at water-subsaturated conditions (RHw = 94 %), relevant for the formation of ice clouds, and in the water-supersaturated regime (RHw = 104 %) to represent ice formation occurring under mixed-phase cloud conditions. In winters 2015 and 2016 the median INP concentrations at RHw = 94 % was below the minimum detectable concentration. At RHw = 104 %, INP concentrations were an order of magnitude higher, with median concentrations in winter 2015 of 2.8 per standard liter (std L−1; normalized to standard T of 273 K and pressure, p, of 1013 hPa) and 4.7 std L−1 in winter 2016. The measurements are in agreement with previous winter measurements obtained with the Portable Ice Nucleation Chamber (PINC) of 2.2 std L−1 at the same location. During winter 2015, two events caused the INP concentrations at RHw = 104 % to significantly increase above the campaign average. First, an increase to 72.1 std L−1 was measured during an event influenced by marine air, arriving at the JFJ from the North Sea and the Norwegian Sea. The contribution from anthropogenic or other sources can thereby not be ruled out. Second, INP concentrations up to 146.2 std L−1 were observed during a Saharan dust event. To our knowledge this is the first time that a clear enrichment in ambient INP concentration in remote regions of the atmosphere is observed during a time of marine air mass influence, suggesting the importance of marine particles on ice nucleation in the free troposphere.

Highlights

  • Clouds and aerosols continue to cause the largest uncertainty in the current assessment of global climate change (e.g., Boucher et al, 2013)

  • In winter 2015, the JFJ experienced free troposphere (FT) conditions during 79 % of the sampling time, with no specific increase in ice-nucleating particle (INP) concentrations during boundary layer influence, while in winter 2016 the site was in the FT 92 % of the time and an event of increased INP concentration was observed during boundary layer influence, which is excluded from the comparison of campaign averages in this study

  • We demonstrated that Horizontal Ice Nucleation Chamber (HINC), based on the design of the UT-continuous-flow-diffusion chambers (CFDCs) (Kanji and Abbatt, 2009), was successfully deployed to sample ambient INP concentrations

Read more

Summary

Introduction

Clouds and aerosols continue to cause the largest uncertainty in the current assessment of global climate change (e.g., Boucher et al, 2013). Cells or cell fragments and exudates of phytoplankton species were found to be ice active (Knopf et al, 2011; Alpert et al, 2011; Wilson et al, 2015), and biological material during phytoplankton blooms might play an important role for ice nucleation (Prather et al, 2013; DeMott et al, 2016) These marine aerosols can be submicrometer in size In addition to laboratory studies, which aim to understand the physical processes of ice nucleation and determine key aspects of aerosols acting as INPs, it is crucial to quantify the total number concentration of ambient INPs in an environment relevant for clouds containing ice and to address the question of their variability in space and time. Two events of anomalously high INP concentrations from the winter 2015 campaign are discussed to investigate the origin of these INPs

Technical description
HINC validation and verification
Sample preparation
Accuracy of temperature and RH in HINC
Summary of validation and verification experiments
Field measurements
Location
Aerosol particle measurements
Cloud water samples
Back trajectories and source sensitivities
Assessment of free-tropospheric conditions
Results
Field measurements of INPs: winters 2015 and 2016
Case studies
Case 2 February 2015: marine air
Case 6 February 2015
Conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call