Aerosol particles as ice crystal seeds in the troposphere: From nano-pores to clouds
Conferencia de Zamin Kanji
21 de Agosto del 2017 de 12:00 hrs
Aerosols and clouds play an important role for the composition of the Earth’s troposphere. As such their physical and chemical interactions need to be well understood to predict the role of the troposphere in balancing the Earth’s radiation budget and predicting weather and future climate. Aerosols can induce cloud droplet formation, ice crystal formation via heterogeneous or homogeneous nucleation resulting in changing the microphysical properties of a cloud and its ability to persist, dissipate or precipitate. Aerosol physical and chemical properties are important in order to predict how they interact with water and water vapour.
Select aerosol particles called Ice Nucleating Particles (INP) have the required chemical and/or physical properties to induce ice crystal formation in a cloud at temperatures (T) above -38 °C and relative humidity with respect to water (RHw) of 100%. Below this temperature, INPs can induce ice formation for conditions of RHw << 100%. For conditions where T < -38 °C and RHw is close to or approaches 100%, homogeneous freezing can occur, rendering the contribution of INPs to the freezing process negligible.
In this work, we will explore the dependency of particles to act as INPs based on their physical and chemical properties and environmental conditions. Particle morphology on the nanometre scale, composition of micron and sub-micron particles, T and RH will be considered in evaluating the impact on heterogeneous ice nucleation processes. This work aims to answer if currently identified aerosols and ice nucleation mechanisms can explain the abundance of ice in clouds observed in the troposphere? What other processes need to be considered in order to accurately predict ice crystal numbers in the atmosphere. Can we specifically identify which properties constitute an INP and what is the molecular identity of an ice nucleation site? Lastly, can there be one grand unifying ice nucleation theory for heterogeneous ice nucleation? To answer these questions, research is designed via laboratory studies of controlled particle systems and field observations of ambient INPs.