Ultrafine Inorganic Particle Formation in Plasma-Assisted Combustion (NSF PI 2021-2024)
Understanding the evolution and transport of indoor bioaerosols (NSF PI 2020-2023)
Understanding the Vertical Transport and Removal of Aerosols during Deep Convective Events (DOE ASR PI 2020-2023)
1. Characterizing the transport and evolution of indoor bioaerosols
The airborne transmission of indoor pathogens is a critical public health concern. The ongoing COVID-19 pandemic has attracted increased attention to improving indoor air quality control strategies to reduce disease transmission. The CDC and WHO currently believe that airborne transmission of SARS-CoV-2 through the airborne mode, which is by inhaling virus-containing bioaerosols smaller than 5 μm in diameter, is unlikely. However, coughing, sneezing, and speaking generate microscopic aerosols, with more than 90% of them being less than 5 μm in size. The objective of this research is to study the evolution and transport of indoor bioaerosols through controlled laboratory experiments and model simulation. Experiments conducted in a small-scale chamber and a walk-in environmental chamber will establish the size-dependent load and viability of microorganisms contained in bioaerosols. The information will be utilized to establish and validate a computational fluid dynamics (CFD) model that incorporates the transport and evolution of bioaerosols to predict the infection risk and optimize indoor ventilation design.
2. Understanding the vertical transport of aerosols during deep convective events
Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Globally, free troposphere is a major source of nucleation- and Aitken-mode aerosols due to the enhanced new particle formation rates at high altitudes1. Recent studies have shown deep convective systems are capable of transporting these small aerosols from the free troposphere to the boundary layer by strong convective downdrafts and weaker downward motions in the stratiform regions. These vertically transported aerosols can grow into cloud condensation nuclei (CCN) and play a significant role in the global climate. We are analyzing a multi-year, multi-site measurement record available from the U.S. Department of Energy (DOE) ARM program, including the observations from the 2014/15 Observations and Modeling of the Green Ocean Amazon (GoAmazon) field campaign, the 2018/19 Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, and the long-term measurements collected at the Southern Great Plains (SGP) atmospheric observatory, where deep convective clouds were frequently observed.
3. Early stages of particle formation in high temperature aerosol reactors
Aerosol science and technology enable continual advances in material synthesis and atmospheric pollutant control. Among these advances, one important frontier is characterizing the initial stages of particle formation by real time measurement of particles below 2 nm in size. Sub 2 nm particles play important roles by acting as seeds for particle growth, ultimately determining the final properties of the generated particles. Tailoring nanoparticle properties requires a thorough understanding and precise control of the particle formation processes, which in turn requires characterizing nanoparticle formation from the initial stages. The knowledge on particle formation in early stages can also be applied in quantum dot synthesis and material doping. This project pursued two approaches in investigating incipient particle characterization in systems with aerosol formation and growth: (1) using a high-resolution differential mobility analyzer (DMA) to measure the size distributions of sub 2 nm particles generated from high-temperature aerosol reactors, and (2) analyzing the physical and chemical pathways of aerosol formation during combustion.
4. Combustion synthesis of functional nanoparticles for energy and environmental applications
Compared to conventional approaches for the manufacture of nanoparticles, gas-phase synthesis offers the advantages of high-throughput production, fast processing, and simplicity. Wide applications of these nanomaterials can be found in energy and environmental engineering, and new fields of nanomedicine and nanorobotics have emerged and are expected to flourish. Recent applications of gas-phase synthesized nanomaterials in energy conversion include solar cells, lithium batteries, CO2 photo-reduction, and catalytic combustion of volatile organic compounds. In these applications, the nanomaterials act as a medium for the transport of electrons and ions or as a catalyst promoting the reaction rates. Their properties are a strong function of their structures, and the successful application of gas-phase synthesis requires an adequate degree of tailoring and control of these structures. By controlling the synthesis method, temperature, composition, and reaction time, the structure of the nanomaterials can be fine tuned for better performances in energy conversion applications. Modeling approaches are also developed to validate the synthesis techniques.
5. Laboratory evaluation of low-cost particle sensors for PM measurement, PM sensor network deployment, and data analysis
Particulate matter (PM) is a crucial factor of air quality affecting visibility, human health, and global climate.PM is quantified using PM10, PM2.5, or PM1, according to inhalation and deposition properties in the human respiratory system, representing the mass concentration of particles below 10 μm, 2.5 μm, and 1 μm in aerodynamic size, respectively. Temporal and spatial PM index may differ from each other significantly due to the limited transport coefficient of particles. With prototypes first assembled in smoke detectors and air purifiers decades ago, particle sensors become popular in recent years with the usage of portable PM monitors, due to the remarkably low price of around $ 10 USD and the merging need for “big data”. These low-cost sensors can be used in locating pollution hotspots or generating coarse 3-D map of PM concentrations for individuals, industries, and environmental agencies. The accurate mapping of the PM information in indoor, local, and regional scales can be used to study the health and climate effects of PM. We also established a dashboard showing the real-time PM2.5 concentrations of our sensors: tinyurl.com/efhar2ao