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The Effect of Cirrus Clouds on Climate and ChemistryEPA Grant Number: U915367
Title: The Effect of Cirrus Clouds on Climate and Chemistry
Investigators: Prenni, Anthony J.
Institution: University of Colorado at Boulder
EPA Project Officer: Just, Theodore J.
Project Period: September 1, 1998 through January 1, 2001
Project Amount: $51,352
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Air Quality and Air Toxics , Fellowship - Atmospheric Sciences
The objectives of this research project are to: (1) measure the efficiency of soot as a heterogeneous nucleus for ice formation; and (2) improve the ability of atmospheric models to determine the effect of soot on cirrus cloud formation.
An experimental technique for measuring heterogeneous ice nucleation on soot and sulfuric acid-coated soot particles has been designed. For these experiments, a fluidized bed has been built to generate a constant output (approximately 105 particles per cm3) of dry, solid soot particles in the sub-µm size range. Particles generated using the fluidized bed are coated with sulfuric acid using a linear temperature drop oven. Using this method, solid soot particles and liquid sulfuric acid particles pass through a flow tube oven where high temperature (400°C) vaporizes the sulfuric acid but not the soot. As the aerosol cools, a linear temperature gradient across the oven ensures that each solid particle becomes coated with sulfuric acid, and that sulfuric acid does not homogeneously nucleate. The soot/sulfuric acid particles are exposed to a predetermined amount of water vapor to create a soot/sulfuric acid aerosol of desired composition. The aerosol passes into a temperature-controlled flow tube where ice nucleation from the mixed aerosol can be monitored using Fourier transform infrared (FTIR) spectroscopy at tropospheric temperatures and humidities. From these experiments, we will determine the efficiency of soot as a heterogeneous nucleus for ice.