Ice nucleation; Aerosol-cloud interaction; Laboratory and field studies; Clouds; Mineral Dust; Freezing; Aerosol-Cloud-Interactions
Kanji Zamin, Welti André, Chou Cédric, Stetzer Olaf and Lohmann Ulrike (2013), Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles, in Atmos. Chem. Phys.
Chou C., Stetzer O., Weingartner E., Juranyi Z., Kanji Z.A. and Lohmann U (2011), Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps, in Atmos. Chem. Phys.
Ladino L., Stetzer O., Lüönd F., Welti A., Lohmann U., Contact freezing experiments of kaolinite particles with cloud droplets, in Journal of Geophysical Research
Ladino Luis, Stetzer Olaf, Hattendorf Bodo, Günther Detlef, Croft Betty, Lohmann Ulrike, Experimental Study of Collection Efficiencies between Submicron Aerosols and Cloud Droplets, in Journal of the Atmospheric Sciences
Hoyle C.R., Pinti V., Welti A., Zobrist. B., Marcolli C., Luo B., Hoeskuldsson A., Mattsson H.B., Stetzer O., Thorsteinsson T., Larsen G., Peter T., Ice nucleation properties of volcanic ash from Eyjafjallajokull, in Atmospheric Chemistry and Physics
, 11(18), 9911-9926.
The formation of ice is an important factor, which determines the microphysical and radiative properties of clouds. As a consequence, the lifetime of clouds and precipitation patterns are influenced and ultimately the climate. Ice can form by homogeneous freezing or by heterogeneous nucleation on pre-existing airborne particles. Heterogeneous nucleation may be sub-divided into three mechanisms. Some aerosol particles like mineral dusts from desert regions are known to be good ice nuclei. The radiative forcing of greenhouse gases is generally well understood but there is still a lack of knowledge about the influence of anthropogenic aerosol emissions on clouds and their respective radiative forcings through the so-called aerosol indirect effect. The formation of ice is one of the largest uncertainties in this context. For example, anthropogenic emissions can lead to an increase in ice nuclei and accelerate precipitation by enhancing the formation of precipitation-sized particles through the Bergeron-Findeisen process. On the other hand, emissions of soluble aerosols or trace gases can reduce the efficiency of natural ice nuclei to initiate freezing with an opposite effect on climate. A greater understanding of the ice nucleation mechanism and the effect of anthropogenic emissions on it is required in order to improve our ability to simulate these processes. With an improved knowledge it will be possible to assess if the net effect of the anthropogenic aerosol enhances or reduces its ability to form ice in clouds and to estimate the respective radiative forcings. In this proposal, we will address the following questions:1.Which aerosol is most active in which heterogeneous freezing mechanism?2.In which direction and to which degree is their ice nucleation activity influenced by atmospheric trace gases and organic components?3.Can these ageing processes be linked to certain chemical signatures in these aerosols?4.Can we use the chemical signatures of ice nuclei found in the laboratory to understand ice nuclei measurements obtained in the field?The complex nature of the nucleation mechanism, for which there is still no comprehensive theoretical model available yet, suggests a step-wise approach under idealized and well controlled conditions in a laboratory setting. Hence, we propose a set of ice nucleation experiments with surrogates for well-known atmospheric ice nuclei like kaolinite, montmorillonite, illite in the laboratory, where different ice nucleation mechanisms will be studied simultaneously. The effects of anthropogenic emissions will then be studied by the controlled exposure of these aerosols to various reactive gases like NH3, O3, SO2, NO, and NO2. These aged aerosols will then again be measured with our ice nucleation instruments. In parallel, the aerosols will be physically and chemically characterized. The conditions for ageing will then be modified stepwise towards more complex scenarios including organic substances and colder temperatures, which are more realistic to the real atmosphere. Time permitting, other aerosols will also be studied such as mineral dusts sampled from different deserts or combustion related particles like soot. Parallel to these measurements, our ice-nucleus counter PINC will be coupled to an aerosol mass spectrometer (ATOFMS) with a counterflow virtual impactor. This combination will allow us to measure the chemical signature of those particles, which had formed ice in the PINC instrument. This combination will first be tested and characterized in the laboratory using the aerosols from the above-mentioned ageing experiments. In a final step, the coupled PINC-ATOFMS system and other instruments will be deployed in a field campaign to study ice nucleation with ambient aerosols. The data taken here will be compared with our laboratory data to identify chemical signatures and to understand the dominant ice nuclei population in the real atmosphere.