AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Laboratory Measurements of the Removal of Interstitial Aerosol in a Cloudy Turbulent Environment
SARITA KARKI, Will Cantrell, Kamal Kant Chandrakar, David Ciochetto, Gregory Kinney, Raymond Shaw, Michigan Technological University
Abstract Number: 138 Working Group: Aerosols, Clouds, and Climate
Abstract Aerosol properties such as number concentration, chemical composition and size influence many cloud properties including the probability for precipitation and hence the cloud’s lifetime. Also, an increase in the number of aerosol particles can lead to an increase in cloud droplet number and decrease the effective droplet radius, which results in an increase in the cloud's albedo for a constant liquid water path. In response, clouds serve as a dominant removal mechanism for intermediate sized aerosol particles. This feedback between aerosol and cloud is the process of cloud cleansing through which, for example, cloudy, polluted air from a continent is slowly transformed into cloudy, clean air of a maritime environment.
We have simulated this process and measured aerosol-cloud feedbacks in Michigan Tech’s cloud chamber, where we can create and sustain a mixing cloud for hours to days. In these experiments, once cloud properties reach steady state, the aerosol source is turned off to initiate the cloud cleansing process. The decay in cloud and aerosol properties are then recorded as a function of time.
Our data suggest that for aerosol particles with dry diameters between about 40 and 100 nm, the principal removal mechanism is activation which proceeds in a two-stage process; i.e. decay of interstitial aerosol concentration occurs slowly at first, then more rapidly as the cloud becomes cleaner. Smaller particles of diameters about 10 to 20 nm are not activated as readily, but removed through convective diffusion to cloud droplets. (Particles of this size are also lost by diffusion to chamber surfaces.) The cloud cleansing process thus demonstrates a simplified version of evolution of polluted clouds to a maritime state.