Aerosol particle light scattering at a perturbed mid-latitude continental northern hemisphere site and its dependence on relative humidity, wavelength of light, particle size and composition
Koloutsou-Vakakis, Sotiria
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https://hdl.handle.net/2142/22149
Description
Title
Aerosol particle light scattering at a perturbed mid-latitude continental northern hemisphere site and its dependence on relative humidity, wavelength of light, particle size and composition
Author(s)
Koloutsou-Vakakis, Sotiria
Issue Date
1996
Doctoral Committee Chair(s)
Rood, Mark J.
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Environmental Sciences
Language
eng
Abstract
Recent model predictions indicate that sulfate aerosol particles cause radiative forcing of the same magnitude but of opposite sign than the forcing caused by anthropogenic greenhouse gases. The spatial and temporal variability of parameters used in the models are highly uncertain resulting in uncertain model predictions of the aerosol radiative forcing. Such parameters related to aerosol particle properties and direct radiative forcing are: the hygroscopic growth factor (f(RH)), the upscatter fraction ($\beta$), and the mass scattering efficiency, ($\alpha$). These three parameters can be estimated from regional measurements of total light scattering and back-scattering coefficients as functions of relative humidity, particle composition and size, and wavelength of light.
To take and validate such measurements: (i) an ambient aerosol monitoring station was designed and built for continuous ambient aerosol measurements, south of Bondville, in Central Illinois, U.S.A., (ii) instrumentation that measures aerosol particle light scattering coefficients under controlled relative humidity conditions was designed, built, calibrated and tested, (iii) a model was developed that estimates hygroscopic particle growth under the assumption of thermodynamic equilibrium and for metastable particles, (iv) experiments with laboratory generated aerosol particles were completed to calibrate the instrumentation and test the models, and (v) tests for closure were completed using the experimental and modeled results.
Examination of the measurements to date, showed that about 95% of the aerosol gravimetric mass (dp $\le$ 1 $\mu$m), at Bondville, that is identifiable with ion chromatography consists of NH$\sb4\sp+$ and SO$\sb4\sp{2-}$. Mean values and standard deviations for f(RH) were in the range 1.1 $\pm$ 0.4 to 2.3 $\pm$ 1.1 depending on wavelength and direction of scattering. Mean values and standard deviations for b were in the range 7.0% $\pm$ 1.4% to 21.7% $\pm$ 4.18% depending on relative humidity and wavelength. $\rm\alpha\sb{so\sbsp{4}{2-}}$ (estimated with multiple linear regression) was 8.25 m$\sp2$/g.
A model, was developed to test closure. The model integrates results from thermodynamic equilibrium calculations and experimental data on metastable particles, with light scattering modeling. Tests for closure indicated that the water insoluble component of the aerosol, which is not accounted for by ion chromatography, can be very important in modifying the optical properties of the aerosol.
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