RP 8: Chemical and mineralogical characterization of ice nuclei and ice particle residuals

PD Dr. Martin Ebert

Institute for Applied Geosciences, Technical University Darmstadt

Prof. Dr. Stephan Weinbruch

Institute for Applied Geosciences, Technical University Darmstadt

Dr. Heinz Bingemer

Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt/Main

Assistance: Daniel Weber (PhD student), Anja Danielczok (PhD student)

The Environmental Scanning Electron Microscope (ESEM) is one of our major tools to characterize ice nucleating particles (INP) and ice particle residuals (IPR) chemically and mineralogically in environmental samples. During INUIT-1 we analyzed INP and IPR by coupling the ESEM to various instruments that allow to discriminate INP, ice crystals or IPR from the total airborne aerosol particles, such as

• the Fast Ice Nucleus chamber FINCH (University of Frankfurt, RP1)
• the ICE Counter-flow Virtual Impactor ICE-CVI (TROPOS,  Leipzig, RP2)
• the Ice-Selective Inlet ISI (Paul Scherer Institute, external partner)
• the Ice Nucleus counter FRIDGE (University of Frankfurt, RP8)

FINCH is a dynamic flow reactor that activates airborne INP into ice crystals for subsequent counting and for collection onto substrates. ICE-CVI and ISI are virtual impactors that separate small ice particles in a counterflow of a dry air from unactivated aerosol.  INP and IR are then collected by inertial separation in a nozzle-type impactor onto boron substrates for SEM analysis. FRIDGE is a system which first precipitates aerosol particles electrostatically onto Si substrates, followed by activation of INP on a cold stage, photography (Figure 1), counting and ESEM analysis.

The chemical composition, mixing-state, morphology and size of INP/IPR is studied in detail by electron microscopy of individual particle analysis. Additionally information about the mineralogical phase composition of silicate particles will be obtained by transmission electron microscopy. To improve quality and comparability of all results instrument intercomparison workshops at the AIDA laboratory (RP7) and in open air at Storm Peak Laboratory (CO, U.S.A.) were conducted in 2015.

During INUIT Phase 2, INP/IPR samples for electron microscopy characterization will be received by all 4 methods during “in-cloud” and “out-of-cloud” measurement periods at the Jungfraujoch research station, Switzerland in 2017 and by FINCH and FRIDGE during an “out-of-cloud” experiment in 2016 in Cyprus.

ESEM analysis and the FRIDGE sampling strategy are combined in long term measurements at the Taunus Observatory site to address the following questions in a ‘climatological’ sense:

• what is the mean abundance and seasonal variability of deposition/condensation freezing INP over central Europe as a function of airmass, trajectory, local parameters?
• Which components (mineral dust, metals, biological particles, soot) make up the main composition of INP? Is it seasonally variable?
• Is the abundance and nucleation property (i.e. activated fraction) of atmospheric INP affected by anthropogenic emissions of urban Frankfurt?
• What are the relative contributions of immersion INP vs. deposition INP?

Furthermore, the Darmstadt group of RP8 will continue to collect and characterize (XRD and ESEM) large amounts of ambient aerosols (up to several grams), which are suitable to be used in lab campaigns in LACIS and AIDA. This way, for the first time lab experiments will be performed with ambient aerosols instead of standard or artificial aerosols.