Date of Award
Spring 2023
Project Type
Dissertation
Program or Major
Chemistry
Degree Name
Doctor of Philosophy
First Advisor
Margaret Greenslade
Abstract
Aerosols are important because of their direct and indirect impact on the energy budget of Earth. Characterizing and understanding the physical, chemical, and optical properties of aerosols is beneficial to decrease uncertainties on the Earth’s energy budget estimations and improve climate models. Field studies characterize the real conditions and cases; however, controlling all variables, including the weather, is impossible, so only a snapshot can be obtained. Laboratory work can be a great support for field studies because controlling experimental conditions on a smaller scale is easier and targets can be achieved. Laboratory optical property studies of aerosol, even single chemical aerosol components, allow the development of scientific knowledge and direct connections so field cases can be represented by models. Here, vanillic acid, which is a biomass burning tracer that can be characterized as carbonaceous was the chemical target. Its physical property, the complex refractive index (CRI) across the wavelength ranges from 270-600 nm, which is important in climate calculations and can be used to calculate optical properties was determined from two particle generation methods. First, the imaginary part, k values, of the CRI were obtained. For wet generation, the k values were calculated from the UV/Vis absorption of vanillic acid solutions, while for dry generation, the UV/Vis reflectance of vanillic acid powder was used. The obtained k values for the wet and dry generation methods were in the range of 0.000-0.388 and 0.000-0.498, respectively. Then, the aerosol extinction differential optical absorption spectrometer (AE-DOAS) was used with a scanning mobility particle sizer (SMPS) to obtain extinction and particle size distribution of the aerosol samples, respectively. By merging the experimental results with Mie theory in closure, the real part of the CRI, n values, was obtained. Several experimental factors within the experimental setup were carefully constrained, characterized, and optimized. Focused consideration was given to the particle size distributions. The n values were found across the wavelengths from 270-600 nm to be 1.65-1.43 for wet-generated vanillic acid, but for dry-generated aerosol, the n values are 1.49-1.66 in wavelengths between 330-600 nm. Generally, the dry-generated particles have a larger n value in comparison to the wet-generated samples at a single wavelength. The potential origins of the differences are discussed though it should be noted that the error bars are overlapping. The obtained n values for vanillic acid are also compared with the previously reported values for organic and brown carbon and show good agreement.
Recommended Citation
Hosseinpour Hashemi, Vahid, "A COMPARISON OF THE SPECTROSCOPICALLY DETERMINED COMPLEX REFRACTIVE INDICES ACROSS UV/VIS WAVELENGTHS FOR VANILLIC ACID FROM TWO AEROSOL GENERATION METHODS" (2023). Doctoral Dissertations. 2765.
https://scholars.unh.edu/dissertation/2765