Influence of Aerosol Chemical Composition and Size on Heterogeneous Ice Formation under Mid-Upper Troposphere Conditions
Event details
| Date | 21.07.2011 |
| Hour | 09:15 |
| Speaker | Zaminhussein Kanji |
| Location | |
| Category | Conferences - Seminars |
Atmospheric aerosols play a pivotal role in climate and air quality. One key uncertainty in predicting future climate is the contribution of various chemical and physical processes to the radiative balance of the Earth. In particular the physical properties of aerosols such as size and solubility and chemical properties such as surface/bulk reactivity resulting in chemical composition changes. Depending on these properties aerosols are involved in cooling/warming the atmosphere directly via interaction with incoming solar radiation (aerosol direct effect) or via their ability to act as cloud condensation or ice nuclei and thus play a role in cloud formation (indirect effect). Ice nuclei are particles that trigger ice formation on their surface either directly from the vapour or liquid phase (heterogeneous ice nucleation).
The current work addresses how the chemical composition and size/surface area of various tropospherically relevant aerosols influence conditions of temperature (T) and relative humidity (RH) required for heterogeneous ice formation conditions in the mid-upper troposphere regime (253 – 220K)? Motivation for this comes first the importance of being able to predict ice formation accurately so as to understand the hydrological cycle since the ice is the primary initiator of precipitation forming clouds. Second the tropospheric budget of water vapour an especially active greenhouse gas is strongly influenced by ice nucleation and growth. Third ice surfaces in the atmosphere act as heterogeneous surfaces for chemical reactions of trace gases (e.g. SO2 O3 NOx) and therefore being able to accurately estimate ice formation rates and quantify ice surface concentrations will allow a more accurate calculation of trace gas budgets in the troposphere.
Ice formation measurement techniques and aerosol generation methods were developed validated and implemented in order to address the above question. A number of tropospherically relevant particulates with naturally-varying and laboratory-modified surface chemistry/structure were investigated for their ice formation efficiency based on highest T and lowest RH required for ice formation.
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- Christina Treier