The proponents of non-conventional lightning protection devices claim that these devices are superior to the conventional Franklin Rod. Lack of systematic study and insufficient field data make it difficult to compare the non-conventional lightning protection devices with the conventional ones. Previously, the performance of various air terminals was studied by comparing the emission current through various dissipation devices in the MSU High Voltage Laboratory. The study of emission current from the air terminals gives an idea about the space charge developing over them. However, it does not show the behavior of air terminals to attract or repel lightning strikes. The present study presents the measurements of critical flashover (CFO) voltage of the air terminals. The CFO voltage shows the ability of an air terminal to attract or reduce the chance of lightning strike to the protected object.

The Covid-19 pandemic heightened attention to airborne microorganisms and their widespread impacts. This dissertation examines two facets about airborne microorganisms: (1) dissemination of antimicrobial resistance in the environment and (2) ionization for disinfection of indoor air. Antimicrobial resistance (AMR) poses a significant threat to public health, exacerbated by the dissemination of antibiotic resistance genes (ARGs) in the atmosphere to an extent that is not yet well understood. Chapters 2 and 3 of this dissertation characterize ARGs in the atmosphere through a literature review and experimental observations at two agricultural sites, respectively. A critical review of 52 studies revealed that ARGs are present in aerosols in urban, rural, hospital, industrial, wastewater treatment plants, composting and landfill sites, and indoor environments. Commonly studied genes include sul1, intI1, beta-lactam ARGs, and tetracycline ARGs, with abundances varying by season and setting. Temporal trends varied based on the type of environment and human activity. Characterization methods included qPCR, ddPCR, and metagenomic analysis; standardized methodologies are needed to unify findings about the dissemination of ARGs in the atmosphere. To address knowledge gaps identified in the literature review, we designed an experimental study at a dairy farm and swine farm, where beta-lactam was the dominant antibiotic used. We quantified ARG concentrations, size distributions, and emission rates in the air and related these to ARGs found in nearby water and soil samples over four seasons. Concentrations of most ARGs were higher during warmer months but varied more by sampling location or exhaust fan usage than time of year. At both farms, blaCTX-M1 concentrations peaked at 104 gene copies per cubic meter (gc m-3), while the exhaust from a building at the swine farm contained genes like intI1, ermF, and qnrA at concentrations up to 105 gc m-3. ARGs were found in aerosol particles of all sizes, and the fraction in coarse particles (>5 m) was enhanced near emission sources. The presence of ARGs in fine (<1 m) and accumulation mode (1-5 m) particles indicates potential for long-range transport. Emission rates reached ~105 gc s-1 for some ARGs, including blaCTX-M1, and 106 gc s-1 for intI1. Inhalation exposure to blaCTX-M1 was comparable to ingestion exposure from soil at the dairy farm. In chapter 4, the effectiveness of an in-duct, bipolar ionization system for reducing airborne pathogens was evaluated in a real-world setting: an in-use lecture hall at a university. There were no significant differences in positive, in-room ion concentrations between periods with the ionizer turned on and turned off; however, negative, in-room ion concentrations were significantly lower when the ionizer was on with constant fan speed. To account for day-to-day variability in total bacteria concentrations, related to occupancy and other factors, we examined the ratio of bacterial colony forming units to 16S rRNA gene copies (CFU gc–1). There were no significant differences in this ratio whether the ionizer was on or off, suggesting limited real-world effectiveness of the treatment technology. Factors such as occupancy and the heating, ventilation, and air conditioning (HVAC) system emerged as the primary drivers of bacterial load in the air. This study highlights the need for further research to validate the potential of ionization to reduce levels of airborne pathogens. / Doctor of Philosophy / The COVID-19 pandemic brought greater awareness of microorganisms in the air and their effects on our health. This dissertation explores two main topics: how antimicrobial resistance spreads in the environment and disinfection of indoor air. Antimicrobial resistance (AMR) is a major public health issue, worsened by the spread of antibiotic resistance genes (ARGs) in the environment. We lack complete understanding of how these genes spread through the air in different places. Chapters 2 and 3 of this dissertation examine ARGs in the air through a literature review and experimental observations at two different farm sites. A review of 52 studies revealed that ARGs are present in the air in urban, rural, hospital, industrial, wastewater treatment plants, composting and landfill sites, and indoor environments. Certain genes were studied more frequently, particularly those associated with antibiotics that have been used for many years, such as penicillin. The concentrations of ARGs in the air varied by season and setting. The genes were detected using three standard biological tests: qPCR, ddPCR, and metagenomic analysis. Standardized methods are needed to gain more information about these genes. To address knowledge gaps identified in the literature review, we designed an experimental study at a dairy farm and swine farm. We measured the levels of ARGs in the air and compared them to those found in nearby water and soil samples over four seasons at each farm. The levels of most ARGs were higher during warmer months. However, their levels were more affected by the sampling location or exhaust fan usage than time of year. At both farms, blaCTX-M1, the ARG associated with the antibiotic used most onsite, was detected at high levels, along with high levels of other genes associated with other types of antibiotics. ARGs were found in particles of all sizes, with larger particles near sources of emissions. Some ARGs could travel long distances in the air. In terms of the amount taken into the body, breathing in blaCTX-M1 at the dairy farm was similar to ingesting it from soil. In chapter 4, we tested an ionization system in a classroom to see if it could reduce airborne pathogens. There were no significant differences in positive ion levels whether the ionizer was on or off, but negative ion levels were lower when the ionizer was on. Normalized bacterial levels did not change significantly, suggesting that the ionizer had limited effectiveness in real-world conditions. Factors like room occupancy and settings of the air handling system had a bigger influence on bacterial levels in the air. More research is needed to confirm the effectiveness of ionization for reducing airborne pathogens in different settings.