Zhaobo Zhang

With the increasing number of electric vehicles taking to the roads, the impact of tailpipe emissions on air quality will decrease, while resuspended road dust and brake/tire wear will become more significant. This study quantified PM₁₀ emissions from tire wear under a range of real highway conditions with measurements across different seasons and roadway surface types in Phoenix, Arizona. Tire wear was quantified in the sampled PM₁₀ using benzothiazoles (vulcanization accelerators) as tire markers. The measured emission factors had a range of 0.005–0.22 mg km⁻¹ veh⁻¹ and are consistent with an earlier experimental study conducted in Phoenix. However, these results are lower than values typically found in the literature and values calculated from emissions models, such as MOVES (MOtor Vehicle Emission Simulator). We found no significant difference in tire wear PM₁₀ emission factors for different surface types (asphalt vs. diamond grind concrete) but saw a significant decrease in the winter compared to the summer.

Occupational exposure to airborne nanoparticles in semiconductor-manufacturing facilities is of growing concern. Currently, comprehensive information regarding atmospheric concentrations, potential origins, and the physical and chemical properties of nanoparticles in these industrial settings is lacking. This study investigated the occurrence of airborne nanoparticles within a semiconductor-research and -manufacturing facility, during both routine operation and maintenance activities. A Scanning Mobility Particle Sizer was used to monitor size-resolved airborne-nanoparticle number concentrations spanning the range of 6 to 220 nm. Breathing zone filter samples were also collected during maintenance processes and underwent subsequent analyses via Transmission Electron Microscopy and Inductively Coupled Plasma Mass Spectrometry, to discover the size, morphology, and chemical composition of the observed nanoparticles. The findings reveal low levels of airborne nanoparticles during routine operations, but maintenance tasks resulted in substantial concentration surges particularly for plasma-enhanced chemical vapor deposition tools with concentrations up to 11,800 particles/cm³. More than 80% of observed particles were smaller than 30 nm. These smallest particles were predominately composed of metals such as iron, nickel, and copper. Moreover, larger particles above 100 nm were also identified, comprising process-related materials such as silicon and indium. Comparative assessment against established mass-based exposure limits did not yield any exceedances. Current exposure limits do not typically consider size though, and the preponderance of small nanoparticles (<30 nm) would warrant a more size-differentiated exposure-risk assessment.

The emergence of facial masks as a critical health intervention to prevent the spread of airborne disease and protect from occupational nanomaterial exposure highlights the need for fundamental insights into the interaction of nanoparticles (f) in the range of −10 V to −800 V were measured by an electrostatic voltmeter and used for testing. Results show that the mask filtration efficiency is highly dependent on the mask surface potential as well as the charge on the challenge aerosol, ranging from 60% to 98%. Eliminating the surface charge results in a maximum 43% decrease in filtration efficiency, emphasizing the importance of electrostatic charge interactions during the particle capture process. Moreover, increased humidity can decrease the surface charge on filters, thereby decreasing the mask filtration efficiency. The knowledge gained from this study provides insight into the critical role of electrostatic attraction in nanoparticle capture mechanisms and benefits future occupational and environmental health studies.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an elusive and highly pathogenic agent, has resulted in the ongoing COVID-19 pandemic affecting numerous populations worldwide. New studies investigating the tenacity of SARS-CoV-2 have highlighted its ability to persist on a myriad of surfaces for several days, including gowns and shoes. As a result, there is a global need for sterilization of a variety of potentially-contaminated items, ranging from clothing to personal protective equipment like face coverings. To this end, we have designed and constructed a cost-effective, scalable, and sustainable sterilization system that uses ozone gas to inactivate viral particles. We sought to determine the efficacy of the system in the sterilization of viral particles as well as its ability to sterilize N95 respirators for reuse. N95 respirators inoculated with P22 bacteriophage and sterilized in the ozone system showed a 6-log ₁₀ reduction in viral load when treated at 25 ppm for 150 minutes. Further, N95 respirators treated with five 150-minute cycles at 35 ppm for a total concentration-time product (CT) of 26,250 ppm min in the ozone system showed comparable filtration efficiency to untreated N95 respirators in a 50 to 200 nmr particulate challenge filtration test. Interestingly, the surgical N95 respirators tested showed complete inactivation of fluid resistance and degradation of the elasticity of polyisoprene straps after five cycles in the sterilization system. Taken together, these data suggest that while our ozone system may negatively affect certain protective aspects of surgical N95 respirators, it does effectively sterilize viral particles and can be utilized for a multitude of other use cases, including sterilizing polypropylene face coverings after potential SARS-CoV-2 contamination. In addition to providing long-term environmental benefits, deployment of this system during the ongoing pandemic reduces the risk of COVID-19 community transmission while conserving monetary resources otherwise spent on the continuous purchase of disposable face coverings.

Due to the virulence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen responsible for the respiratory disease termed COVID-19, there has been a significant increase in demand for surgical masks and N95 respirators in medical clinics as well as within communities operating during the COVID-19 epidemic. Thus, community members, business owners, and even medical personnel have resorted to alternative methods for sterilizing face coverings and N95 respirators for reuse. While significant work has shown that vaporized hydrogen peroxide (VHP) can be used to sterilize N95 respirators, the cost and installation time for these sterilization systems limit their accessibility. To this end, we have designed and constructed a novel, cost-effective, and scalable VHP system that can be used to sterilize N95 respirators and other face coverings for clinical and community applications. N95 respirators inoculated with P22 bacteriophage showed a greater than 6-log ₁₀ reduction in viral load when sterilized in the VHP system for one 60-minute cycle. Further, N95 respirators treated with 20 cycles in this VHP system showed comparable filtration efficiency to untreated N95 respirators in a 50 to 200 nanometer particulate challenge filtration test. While a 23% average increase in water droplet roll-off time was observed for N95 respirators treated with 5 cycles in the sterilization, no breakdown in fluid resistance was detected. These data suggest that our VHP system is effective in sterilizing N95 respirators and other polypropylene masks for reuse. Relating to the present epidemic, deployment of this system reduces the risk of COVID-19 community transmission while conserving monetary resources otherwise spent on the continuous purchase of disposable N95 respirators and other face coverings. In summary, this novel, scientifically validated sterilization system can be easily built at a low cost and implemented in a wide range of settings.