Uncertainty in counting ice nucleating particles with continuous flow diffusion chambers

Sarvesh Garimella,Robert O David,Daniel A Rothenberg,Michael Rösch,Martin J Wolf,Daniel J Cziczo,Chien Wang,Zamin A Kanji

doi:10.5194/acp-17-10855-2017

Abstract

Abstract. This study investigates the measurement of ice nucleating particle (INP) concentrations and sizing of crystals using continuous flow diffusion chambers (CFDCs). CFDCs have been deployed for decades to measure the formation of INPs under controlled humidity and temperature conditions in laboratory studies and by ambient aerosol populations. These measurements have, in turn, been used to construct parameterizations for use in models by relating the formation of ice crystals to state variables such as temperature and humidity as well as aerosol particle properties such as composition and number. We show here that assumptions of ideal instrument behavior are not supported by measurements made with a commercially available CFDC, the SPectrometer for Ice Nucleation (SPIN), and the instrument on which it is based, the Zurich Ice Nucleation Chamber (ZINC). Non-ideal instrument behavior, which is likely inherent to varying degrees in all CFDCs, is caused by exposure of particles to different humidities and/or temperatures than predicated from instrument theory of operation. This can result in a systematic, and variable, underestimation of reported INP concentrations. We find here variable correction factors from 1.5 to 9.5, consistent with previous literature values. We use a machine learning approach to show that non-ideality is most likely due to small-scale flow features where the aerosols are combined with sheath flows. Machine learning is also used to minimize the uncertainty in measured INP concentrations. We suggest that detailed measurement, on an instrument-by-instrument basis, be performed to characterize this uncertainty.

Highlights

Aerosol particles affect the climate system via their ability to interact with radiation and act as the sites upon which water condenses to form liquid and ice clouds (Pruppacher and Klett, 1997; Seinfeld and Pandis, 2006; Boucher et al, 2013)
The results presented here indicate that neither the reported thermodynamic conditions nor results from a single timing test capture the full variability of flam in the SPectrometer for Ice Nucleation (SPIN) Continuous flow diffusion chambers (CFDCs)
We show that it is variable in Zurich Ice Nucleation Chamber (ZINC) and SPIN

Summary

Introduction

Aerosol particles affect the climate system via their ability to interact with radiation and act as the sites upon which water condenses to form liquid and ice clouds (Pruppacher and Klett, 1997; Seinfeld and Pandis, 2006; Boucher et al, 2013) Those that facilitate ice crystal formation above the temperature or below the humidity of homogeneous freezing are called ice nucleating particles (INPs) and affect the formation and persistence of mixed-phase and cirrus clouds (Forster et al, 2007). Measurements of INP concentration using CFDCs have been used to construct model parameterizations that relate the formation of ice crystals to temperature and aerosol particle number and size (DeMott et al, 2010, 2015; Tobo et al, 2013). The use of CFDC data for parameterization of ice formation in such models highlights the need for assessing the accuracy and bias of such measurements

Methods

Results

Conclusion