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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2022)

Anthropogenic trace gases such as greenhouse gases and air toxics emitted to the atmosphere contribute to radiative forcing, degradation of air quality, and negative impacts on human health. Quantification and characterization of these important trace gases are required to mitigate the global climate crisis and improve the air quality. My dissertation focuses on constraining methane (CH4) emissions from California’s San Joaquin Valley (SJV) dairy farms and characterizing wildfire emissions using ground-based solar spectroscopy observations. Additionally, I characterize a portable gas chromatograph coupled to a photoionization detector (GC-PID) for measuring concentrations of air toxics at ambient levels. In the first study, I studied the seasonality of CH4 emissions from dairy farms across four seasons from Spring 2019 to Winter 2020 in the SJV to investigate whether emissions varied across time and to discern the environmental factors driving temporal differences. Measurements collected during different seasons provided insight into the meteorological and management factors that drive the time-varying patterns observed during the year. This research showed that seasonal variability exists within dairy farm emissions and mitigation should focus in the summer. Wildfires are increasing in the Western United States making it critical to understand the impacts of greenhouse gases and air pollutants emitted to the atmosphere. I used a ground-based remote sensing technique to measure the amount of greenhouse gases and aerosol present in the atmosphere. I isolated a large smoke plume from the Sequoia Lightning Fire Complex (SQF) and calculated variables to understand the fuel properties. This revealed that a significant amount of CH4 was emitted from the 2020 wildfire season. In the third study, I characterized the performance of a compact GC-PID and optimize the configuration to detect ambient levels of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). With an analysis time of less than 15 minutes, the compact GC-PID is ideal for field deployment of background and polluted atmospheres for near-real time measurements of BTEX. The results highlight the application of the compact and easily deployable GC-PID for community monitoring and screening of BTEX.

    Cover page: Advances in Atmospheric Trace Gas Monitoring Systems: Quantification of Methane Sources by Solar Column Observations in the San Joaquin Valley of California & Characterization of a Portable Air Toxics SensorCreative Commons 'BY-ND' version 4.0 license
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2021)
    In this study, we test the performance of a compact gas chromatograph with photoionization detector (GC-PID) and optimize the configuration to detect ambient (sub-ppb) levels of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). The GC-PID system was designed to serve as a relatively inexpensive (~10 k USD) and field-deployable air toxic screening tool alternative to conventional benchtop GCs. The instrument uses ambient air as a carrier gas and consists of a Tenax-GR sorbent-based preconcentrator, a gas sample valve, two capillary columns, and a photoionization detector (PID) with a small footprint and low power requirement. The performance of the GC-PID has been evaluated in terms of system linearity and sensitivity in field conditions. The BTEX-GC system demonstrated the capacity to detect BTEX at levels as high as 500 ppb with a linear calibration range of 0-100 ppb. A detection limit lower than 1 ppb was found for all BTEX compounds with a sampling volume of 1 L. No significant drift in the instrument was observed. A time-varying calibration technique was established that requires minimal equipment for field operations and optimizes the sampling procedure for field measurements. With an analysis time of less than 15 min, the compact GC-PID is ideal for field deployment of background and polluted atmospheres for near-real time measurements of BTEX. The results highlight the application of the compact and easily deployable GC-PID for community monitoring and screening of air toxics.
      Cover page: Characterizing the Performance of a Compact BTEX GC-PID for Near-Real Time Analysis and Field Deployment
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2021)
      The dairy industry in the San Joaquin Valley (SJV) is one of California’s largest methane (CH4) sources. Reducing dairy emissions is a priority for the state’s climate change plans. Observations of current dairy CH4 emissions are key to monitoring actions taken toward this goal. To help support this, we present new ground-based measurements of atmospheric column-averaged CH4 mixing ratio (XCH4) gradients across a group of 600 dairies in the central SJV using EM27/SUN solar spectrometers. We used measurements from the 2019 summer and 2020 winter seasons for a top-down emission inversion based on the WRF-STILT model. Our top-down estimates of the region’s dairy emissions range from 90% to 183% of the current CALGEM inventory’s emissions of 277 Gg/yr. In contrast to the strong temperature dependence found by earlier dairy CH4 emission studies, we also find that our top-down emissions during the winter measurement days are comparable to the summer measurement days, possibly due to seasonal changes in dairy management practices and meteorological conditions. Furthermore, we find significant interday variability in our measurements and find that our emission estimates overlap with earlier top-down studies and bottom-up inventories in this region. Our study demonstrates how analysis of ground-based remotely sensed CH4 gradient observations can help improve our understanding of CH4 sources at scales relevant to mitigation policy. It also reflects the need for long-term monitoring of CH4 emissions in the region and at individual facilities to better understand their emissions.
        Cover page: Dairy Methane Emissions in California's San Joaquin Valley Inferred With Ground‐Based Remote Sensing Observations in the Summer and Winter
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2019)
        Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO2) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed <0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10-24% in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective than the vegetation barrier alone, by 6-33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an existing solid barrier results in lower downwind pollution concentrations, especially under low wind speeds when concentrations can be high.
          Cover page: Effectiveness of vegetation and sound wall-vegetation combination barriers on pollution dispersion from freeways under early morning conditions.
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