AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Measurements of Removal Rate of Interstitial Aerosols in a Cloudy, Turbulent Environment
ABU SAYEED MD SHAWON, Gregory Kinney, Prasanth Prabhakaran, Jesse C. Anderson, Raymond Shaw, Will Cantrell, Michigan Technological University
Abstract Number: 51 Working Group: Aerosols, Clouds and Climate
Abstract Aerosol-cloud interactions influence climate by affecting the Earth’s radiative budget; they are an uncertainty in assessing anthropogenic effects on climate change. Since aerosols are one of the required ingredients to form cloud droplets, understanding their removal mechanisms is a key aspect to understand this interaction. Forming cloud droplets (activation) becomes the dominant removal mechanism for aerosols that are too big to be highly diffusive and too small to have an appreciable settling velocity. Traditionally, the probability of activation can be described by the chemical composition and the size distribution of the aerosol using the Köhler equation. However, in a turbulent environment, the temperature and water vapor pressure become fluctuating quantities, and so does the saturation ratio. Hence, considering the effects of fluctuating saturation ratio is important in understanding the activation process of an aerosol along with its size and chemical composition.
We investigated this removal mechanism in Michigan Tech’s turbulent mixing chamber (also known as the π chamber), where we can create sustained cloud conditions through moist Rayleigh Bénard convection. In steady state conditions, we have measured the size distribution of interstitial aerosols, residual particles (i.e., the particles left after sampling and drying cloud droplets), and cloud droplets. All these experiments suggest that in a turbulent environment, since the saturation ratio fluctuates in time and space, there is no longer a sharp correspondence between the size and activation. Therefore, we have considered a numerical approach to obtain an approximation of the saturation ratio and its fluctuation in a system by using hydrated aerosol and droplet size distribution. We have also explored the relative contributions of aerosol number concentration and chemical composition.