Graduation Year
2025
Document Type
Master's Thesis
Degree
Master of Science
Program
Biological Science
Program Director
Patti Culross, MD, MPH
First Reader
Christine Koh, PhD
Second Reader
Randall Hall, PhD
Abstract
Aerosols are small airborne particles that change with changing environments in terms of temperature, pressure, chemicals, pH, and oxygen levels. These changes in aerosols’ physical and chemical properties in real time have been monitored using the techniques of Dynamic light scattering (DLS) and Ultraviolet (UV) absorption spectroscopy. The oxidation of two types of aerosols, bioaerosol and organic aerosol, were studied using the above techniques. Bioaerosols are suspended particulates in the air that either contain living organic components or are biological in nature, including bacteria, viruses, fungi, pollen, and microbial toxins. Among these diverse bioaerosols, bacterial aerosols containing Bacillus cereus or Escherichia coli were studied. Their physical property such as size distribution was monitored after the bacterial aerosols were under oxidative stress. Bacterial aerosols’ size is closely related to their viability with larger bacterial aerosols having higher viability chances. As Bacillus cereus and Escherichia coli are different in sporing and nonsporing, respectively, they were found to form different distributions in aerosol sizes. Although they formed different sized particles, both bacterial aerosols showed two size distributions. The sporing bacterium, Bacillus cereus, produced a spore with the mean size of 914 nm and a larger aggregate with a mean size of 3350 μm. The nonsporing bacterium, Escherichia coli, formed a Smaller fragments at 30 nm in size and a large aggregate with a mean diameter of 170 μm. The two bacterial aerosols responded differently to oxidative stresses caused by 70% isopropanol or 10% bleach. Large aggregates of B. cereus were destroyed by both stressors, but spores of B. cereus were fragmented by 10% bleach or were aggregated into particles of a few spores by 70%isopropanol. Instead of being destroyed, large aggregates of E. coli increased or remained the same size under both stressors, while the small fragments either broke down further or remained intact. This implies that different bacteria, especially sporing and nonsporing bacteria, should be treated differently when airborne to effectively change their viability. These findings are important in the formulation of strategies to reduce the spread of airborne pathogens and understanding their impacts on environmental and human health in general. Organic aerosol is a product of air pollution and consists of volatile organic compounds (VOCs). Catechol, a benzene ring with two hydroxyl (-OH) groups attached to adjacent carbon atoms, is an industrial product and a precursor to toxic polyaromatic hydrocarbons (PAHs) and dangerous radicals. Polymerization of catechol was seen visually as discoloration and spectroscopically. The rate of the polymerization process was controlled to be able see intermediates or products in depth and also to understand the chemistry of catechol that is airborne instead of in bulk solution. The aerosolized catechol showed new results, double peak (at 272 nm and 280 nm) in the UV absorbance spectra, that represents two different electronic transitions, possibly allowed by its intermolecular interaction in cis- or trans- isomer. Oxidation of the catechol aerosol revealed that there are different reaction pathways for when oxygen is deprived (0%) or plentiful (20%). With 20% Oxygen in the air of the solution or aerosol, the aerosol’s absorbance spectra showed no change upon pH changes, but the solution’s absorbance spectra demonstrated extended polymerization in alkaline conditions. When Oxygen was removed from the air, there was an indication that the aromatic ring might have opened to form trans, trans-muconic acid at higher pH with no evidence of discoloration that represents extensive polymerization. Most importantly, with 0% Oxygen in the air, there is a strong possibility that an important radical species in catechol oxidation, the semiquinone radical, is observed in the alkaline conditioned (pH 9 and 11) aerosols.