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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2018)

The exposure to particulate matter (PM) has strong adverse health effects, such as aggravated asthma, decrease in lung function, and increase respiratory symptoms. PM is complex and dynamic in its chemical composition and physical mixing state. The properties of PM have not been thoroughly characterized, and the mechanism of PM causing adverse effect has not been well understood. This study focuses on characterizing physical properties of urban background air particles by analyzing the particle spectra, particle effective density, black carbon, and active surface area along with chemical characterization using AMS. The effective density profiles were used to estimate the respiratory system-deposited ambient particle mass according to lung deposition fraction curve reported by ICRP (1994).

The first study was to determine size-resolved effective densities of ambient aerosols in Riverside, CA for four 7-day periods during 2015 – 2016. The mass of size selected particles (50, 70, 101 and 152 nm) were measured to determine the effective density for particles. A catalytic stripper (CS) in alternating mode was used to remove volatile compounds on the aerosol before density measurements. Aerosol non-refractory composition measurement was conducted in June 2016 campaign to understand the effect of chemical composition on particle density. The average particle densities for all measurement campaigns with CS bypassing mode (BP) were 1.17 g/cm3 at 50 nm and 1.25 – 1.28 g/cm3 at 70, 101 and 152 nm. The average density after CS conditioning (CS mode) showed a decreasing trend from 1.22 g/cm3 to 1.04 g/cm3 withincreasing selected size, and a mass fractal dimension (Df) of 2.85. Both the BP and CS mode particles showed the lowest effective density from 6:00 AM to 9:00 AM and highest density from 11:00 AM to 3:00 PM. The diurnal variation of density became more profound as particle size increases for both sampling modes. The variation was found to be more intense for the CS mode compared than the BP mode. To confirm this observation, organic aerosol and ammonium nitrate mass in the similar size range were tested simultaneously with BP mode. The results showed effective density measurements correlated well with positively (R2=0.78) and negatively (R2=0.62). This study provided an update to the aerosol density profiles of a well-known receptor site (Riverside, CA) and investigated the transformation of particles in different seasons. The obtained effective density profiles were used in the proceeding study in order to effectively estimate the respiratory-deposited ambient aerosol mass.

In the second study, the size distributions and effective densities of ambient particles measured in September 2015 and June 2016 were used to calculate time-dependent lung deposited particulate matter (PM) mass using lung deposition fraction curve reported by ICRP (1994). The particle active surface area, black carbon (BC) mass, particle number (PN), solid particle number (SPN), and suspended PM mass (from particle size distributions and effective densities) were also obtained to investigate correlations with PM dose. Non-refractory organic and inorganic mass measured by an aerosol mass spectrometer (mAMS) provided additional information in relation to dose versus chemical nature of particles.

Ambient particle size distributions showed strong diurnal variations during the sampling period. While the lung deposited PM mass fraction (0.32-0.36) did not vary much with time, lung deposited and suspended PM mass in the ambient air showed similar trend. Deposition in the alveolar region was the highest (0.3-1.0 μg/m3), which was followed by the nasal region (0.16 – 0.83 μg/m3) and tracheobronchial region (0.05 – 0.27 μg/m3). All three regions peaked at 12:00 PM – 6:00 PM and reached the lowest value near midnight.

One of the goals of this study was to consider the most prominent ambient PM measurement method in consideration to health and lung deposition. Suspended PM mass had the highest correlation with respiratory doses, which was followed by organics measured using mAMS, active surface area, and BC mass. It is also found that particle hygroscopicity did not affect correlations between metrics and lung deposited PM mass. By taking into account the accessibility and cost of these measurements, we propose the particle active surface area and BC mass to be considered when evaluating/monitoring the health effects caused by PM.

    Cover page: Investigation of Particle Effective Density, Size Distribution and Dose Metric of Ambient Aerosol
    • Article
    Western Journal of Emergency Medicine: Integrating Emergency Care with Population Health, Volume 23, Issue 1.1 (2022)
      Cover page: In-Person to Remote Transition of the New York University Emergency Medicine Underrepresented in Medicine Fellowship During the COVID-19 PandemicCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      2018 Publications (2018)
        Cover page: Investigation of ambient aerosol effective density with and without using a catalytic stripper
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2015)
        Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.
          Cover page: Atomic scale analysis of the enhanced electro- and photo-catalytic activity in high-index faceted porous NiO nanowires.Creative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          LBL Publications (2022)
          Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counterions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique based on ion exchange, we prepare highly doped films with several counterions of varying size and shape and characterize their carrier density, electrical conductivity, and paracrystalline disorder. In this uniquely large data set composed of several classes of high-mobility conjugated polymers, each doped with at least five different ions, we find electrical conductivity to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parametrized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localization theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disorder-limited nature of charge transport and suggesting new strategies to further improve conductivities.
            Cover page: Structural and Dynamic Disorder, Not Ionic Trapping, Controls Charge Transport in Highly Doped Conducting PolymersCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2018)
            Many countries have been constructing modern ground transportation projects. This raises questions about the impacts of such projects on development of impervious surfaces, yet there have been few attempts to systematically analyze these impacts. This paper attempts to narrow this information gap using the Hangzhou Bay Bridge project, China, as an exploratory case study. Using remotely sensed data, we developed a framework based on statistical techniques, wavelet multi-resolution analysis and Theil-Sen slope analysis to measure the changes in impervious surfaces. The derived changes were then linked to the bridge project with respect to socio-economic factors and land use development activities. The findings highlight that the analytical framework could reliably quantify the area, pattern and form of new urban area and urban intensification. Change detection analysis showed that urban area, GDP and the length of highways increased moderately in the pre-Hangzhou Bay Bridge period (1995–2002) while all of these variables increased more substantially during (2002–2009) and after (2009–2013) the bridge construction. The results indicate that the development of impervious surfaces due to new urban area came at the expense of permeable surfaces in the urban fringe and within rural regions, while urban intensification occurred mainly in the form of the redevelopment of older structures to modern high-rise buildings within existing urban regions. In the context of improved transportation infrastructure, our findings suggest that new urban area and urban intensification can be attributed to consecutive events which act like a chain reaction: construction of improved transportation projects, their impacts on land use development policies, effects of both systems on socio-economic variables, and finally all these changes influence new urban area and urban intensification. However, more research is needed to better understand this sequential process and to examine the broader applicability of the concept in other developing regions.
              Cover page: How do modern transportation projects impact on development of impervious surfaces via new urban area and urban intensification? Evidence from Hangzhou Bay Bridge, China
              • Article
              • Peer Reviewed
              2018 Publications (2018)
                Cover page: Sources of variance in BC mass measurements from a small marine engine: Influence of the instruments, fuels and loads
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