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Open Access Publications from the University of California

Scholarly Works (24 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2021)

Ultrafine particulate matter (UFP; airborne particles with diameter < 0.1 µm) is an emerging air quality concern because particles in this size range are potentially more toxic than larger airborne particles. Measurement networks that can support source apportionment calculations for UFPs have been limited in the past by the high costs for equipment, supplies, and labor. The lack of UFP sampling and chemical analysis limits the understanding of spatial and temporal trends, source contributions and health effects of ambient UFP. In the current study, two co-located cascade impactors collected 3-day averaged UFP mass (PM0.1) for a full year at four sites in California, United States for the measurement of carbonaceous components and elements, respectively. Monthly samples of particles in the diameter range 0.1 – 1.8 µm were also collected. Statistical analyses of the day-of-week trends for PM0.1 components revealed location-specific patterns along with important general trends for UFP concentrations. Source apportionment calculations by Positive Matrix Factorization (PMF) using PM0.1 elements as unique tracers identified seven sources. The major source contributions to total PM0.1 mass were consistent with results generated by Chemical Mass Balance (CMB) using molecular markers as tracers. The feasibility of employing a single cascade impactor loaded with foil substrates for future PM0.1 sampling networks was explored by modifying the extraction method for elements to work on foil substrates. The results of PMF source apportionment calculations carried out with two impactors vs. one impactor were compared. The analyses performed in this study will provide information for understanding PM0.1 emission patterns, investigating their health effects and reducing the costs of sampling to enable larger scale PM0.1 studies in the future.

    Cover page: Ultrafine Particles in California – Weekly Trends, Source Apportionment, and Sampling Implications
    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2021)

    California Assembly Bill 32 (AB32) sets the goal to reduce greenhouse gas (GHG) emissions to a level 80% below 1990 levels by 2050. This deep decarbonization target requires major technology advancement and energy structure transition to a renewable and sustainable future. The environmental aspects of such a transition should be evaluated carefully before major investments in infrastructure are made. Biogas is a promising renewable energy resource in California that shares many similarities with natural gas but with the advantage of being carbon neutral since it generates energy from organic waste. However, biogas contains trace levels of numerous chemical compounds that depend on the feedstock and production process. The air quality implications of using biogas in different situations should be examined carefully before widespread adoption across California.

    The second chapter of this thesis characterizes the chemical and biological composition of raw biogas produced at five facilities using different feedstocks. The toxicity of combusted biogas is tested under fresh and photo-chemically aged conditions. Results find no strong evidence of potential occupational health risk from the five California biogas sites. Results also show no obvious differences between the toxicity of different biogas combustion exhaust after atmospheric dilution and aging. The third chapter of this thesis examines the emissions from the combustion of upgraded biogas that has CO2 removed and CH4 concentrated to be qualified as renewable natural gas (RNG). A light-duty cargo van was tested with CNG and two RNG blends on a chassis dynamometer to compare the toxicity of the resulting exhaust. CNG vehicle engine exhaust showed a higher or similar level of various toxicity responses, and photochemical reactions did not seem to alter the observed trend. These preliminary results suggest that utilizing biogas for direct heat and electricity generation or as vehicle fuel after upgrading could be useful strategies to reduce carbon intensity without negatively impacting air quality or public health.

    The fourth chapter of this thesis extends the scope by modeling air pollutant emissions from all California socio-economic sectors under different energy scenarios in the year 2050. To study the air quality implications of some key resources and technologies in the decarbonization transition, a total of six different scenarios were analyzed for various particulate and gaseous pollutant emissions. These scenarios include: 1) a business-as-usual future reference scenario "BAU", 2) a partial GHG reduction scenario that constrains only through 2030 with 40% reduction "CAP30", 3) a climate-friendly 80% GHG reduction scenario featuring deep penetration of advanced technologies and renewable energies "GHGAi", a same 80% GHG reduction scenario with the deployment of biomass carbon capture and sequestration technology "CCS", and two variation scenarios on GHGAi that examine the effect of using more natural gas in built environment "NGB" and power generation "NGT". Results show that major air quality benefits are expected from the GHGAi scenario, which includes aggressive decarbonization of electricity supply, electrification of most end-use appliances, improvement of appliances efficiency, and deployment of low-carbon transportation fuels and technologies. Bio-CCS technology holds promise as a shortcut to GHG mitigation and the utilization of natural gas bridges the transition from traditional to renewable energy systems, but neither of these technologies appear to be optimal from a future air quality management perspective. Adoption of biogas as an energy source plays a small but constructive role in the overall transition of California’s energy system towards a low carbon future.

      Cover page: Air Quality Implications of Energy Decarbonization and Using Biogas in California
      • Article
      ITS reports (2023)
      Lack of a strong reduction in ambient ozone (O3) concentrations during reduced traffic periods associated with COVID-19 calls into question the conventional wisdom that mobile sources dominate air pollution in California. Fossil-fueledmmotor vehicles emit oxides of nitrogen (NOx) and volatile organic compounds (VOCs) that are precursors to O3 formation, but the chemical reaction system that forms O3 is complex. The ratio of NOx/VOCs determines if the O3 formation regime is NOx-limited (reducing NOx reduces O3) or NOx-rich (reducing NOx increases O3). This project developed new methods to directly measure O3 chemistry in the atmosphere and applied them over long-term campaigns in multiple California cities to quantify traffic contributions to O3 formation. A seasonal-cycle was observed of NOx-rich O3 chemistry during cooler months trending toward NOx-limited chemistry in warmer months. Superimposed on this seasonal cycle was a spatial pattern of NOx-rich chemistry in dense urban cores and NOx-limited chemistry in areas downwind of urban cores. Chemistry-based models with source tagging were also developed to better understand these trends. Seasonal changes to biogenic VOC and gasoline evaporative VOC emissions likely explain the seasonal changes in O3 formation chemistry. Reduced traffic emissions in March 2020 did not reduce O3 concentrations because the chemistry was heavily NOx-rich during the spring season. Extended model predictions suggest that similar traffic reductions could have reduced ambient O3 concentrations in small and intermediate cities if they would have occurred in summer months. Traffic reductions alone would not be sufficient to reduce O3 concentrations in the urban cores of larger cities. Reduced emissions from transportation sources can improve air quality in California, but transportation sources no longer exclusively dominate O3 formation. Future emissions controls should be coordinated across multiple sectors (including transportation) to achieve their objectives.
        Cover page: Measuring Changes in Air Quality from Reduced Travel in Response to COVID-19
        • Article
        Policy Briefs (2022)
          Cover page: Air Quality Impacts of Proposed Changes to Oregon’s Clean Fuels
          • Article
          Reports (2022)
            Cover page: Modeling Expected Air Quality Impacts of Oregon’s Proposed Expanded Clean Fuels Program
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2013)
            Climate change is expected to increase global mean temperatures leading to higher tropospheric ozone (O3) concentrations in already polluted regions, potentially eroding the benefits of expensive emission controls. The magnitude of the "O3-climate penalty" has generally decreased over the past three decades, which makes future predictions for climate impacts on air quality uncertain. Researchers attribute historical reductions in the O3-climate penalty to reductions in NOx emissions but have so far not extended this theory into a quantitative prediction for future effects. Here, we show that a three-dimensional air quality model can be used to map the behavior of the O3-climate penalty under varying NOx and VOC emissions in both NOx-limited and NOx-saturated conditions in Central and Southern California, respectively. Simulations suggest that the planned emissions control program for O3 precursors will not diminish the O3-climate penalty to zero as some observational studies might imply. The results further demonstrate that in a NOx-limited air basin, NOx control strategies alone are sufficient to both decrease the O3-climate penalty and mitigate O3 pollution, while in a NOx-saturated air basin, a modified emissions control plan that carefully chooses reductions in both NOx and VOC emissions may be necessary to eliminate the O3-climate penalty while simultaneously reducing base case O3 concentrations to desired levels. Additional modeling is needed to determine the behavior of the O3-climate penalty as NOx and VOC emissions evolve in other regions.
              Cover page: The Ozone–Climate Penalty: Past, Present, and Future
              • Article
              • Peer Reviewed
              Working Papers (2018)
              The California Regional Multisector Air Quality Emissions (CA-REMARQUE) model is developed to predict changes to criteria pollutant emissions inventories in California in response to sophisticated emissions control programs implemented to achieve deep greenhouse gas (GHG) emissions reductions. Two scenarios for the year 2050 act as the starting point for calculations: a business-as-usual (BAU) scenario and an 80% GHG reduction (GHG-Step) scenario. Each of these scenarios was developed with an energy economic model to optimize costs across the entire California economy and so they include changes in activity, fuels, and technology across economic sectors. Separate algorithms are developed to estimate emissions of criteria pollutants (or their precursors) that are consistent with the future GHG scenarios for the following economic sectors: (i) on-road, (ii) rail and off-road, (iii) marine and aviation, (iv) residential and commercial, (v) electricity generation, and (vi) biorefineries. Properly accounting for new technologies involving electrification, biofuels, and hydrogen plays a central role in these calculations. Critically, criteria pollutant emissions do not decrease uniformly across all sectors of the economy. Emissions of certain criteria pollutants (or their precursors) increase in some sectors as part of the overall optimization within each of the scenarios. This produces nonuniform changes to criteria pollutant emissions in close proximity to heavily populated regions when viewed at 4km spatial resolution with implications for exposure to air pollution for those populations. As a further complication, changing fuels and technology also modify the composition of reactive organic gas emissions and the size and composition of particulate matter emissions. This is most notably apparent through a comparison of emissions reductions for different size fractions of primary particulate matter. Primary PM2.5 emissions decrease by 4% in the GHG-Step scenario vs. the BAU scenario while corresponding primary PM0.1 emissions decrease by 36%. Ultrafine particles (PM0.1) are an emerging pollutant of concern expected to impact public health in future scenarios. The complexity of this situation illustrates the need for realistic treatment of criteria pollutant emissions inventories linked to GHG emissions policies designed for fully developed countries and states with strict existing environmental regulations.
                Cover page: Estimating Criteria Pollutant Emissions Using the California Regional Multisector Air Quality Emissions (CA-REMARQUE) Model v1.0
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2015)

                Background

                Although several cohort studies report associations between chronic exposure to fine particles (PM2.5) and mortality, few have studied the effects of chronic exposure to ultrafine (UF) particles. In addition, few studies have estimated the effects of the constituents of either PM2.5 or UF particles.

                Methods

                We used a statewide cohort of > 100,000 women from the California Teachers Study who were followed from 2001 through 2007. Exposure data at the residential level were provided by a chemical transport model that computed pollutant concentrations from > 900 sources in California. Besides particle mass, monthly concentrations of 11 species and 8 sources or primary particles were generated at 4-km grids. We used a Cox proportional hazards model to estimate the association between the pollutants and all-cause, cardiovascular, ischemic heart disease (IHD), and respiratory mortality.

                Results

                We observed statistically significant (p < 0.05) associations of IHD with PM2.5 mass, nitrate, elemental carbon (EC), copper (Cu), and secondary organics and the sources gas- and diesel-fueled vehicles, meat cooking, and high-sulfur fuel combustion. The hazard ratio estimate of 1.19 (95% CI: 1.08, 1.31) for IHD in association with a 10-μg/m3 increase in PM2.5 is consistent with findings from the American Cancer Society cohort. We also observed significant positive associations between IHD and several UF components including EC, Cu, metals, and mobile sources.

                Conclusions

                Using an emissions-based model with a 4-km spatial scale, we observed significant positive associations between IHD mortality and both fine and ultrafine particle species and sources. Our results suggest that the exposure model effectively measured local exposures and facilitated the examination of the relative toxicity of particle species.
                  Cover page: Associations of Mortality with Long-Term Exposures to Fine and Ultrafine Particles, Species and Sources: Results from the California Teachers Study Cohort
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2013)
                  Eight light-duty gasoline low emission vehicles (LEV I) were tested on a Chassis dynamometer using the California Unified Cycle (UC) at the Haagen-Smit vehicle test facility at the California Air Resources Board in El Monte, CA during September 2011. The UC includes a cold start phase followed by a hot stabilized running phase. In addition, a light-duty gasoline LEV vehicle and ultralow emission vehicle (ULEV), and a light-duty diesel passenger vehicle and gasoline direct injection (GDI) vehicle were tested on a constant velocity driving cycle. A variety of instruments with response times ≥0.1 Hz were used to characterize how the emissions of the major particulate matter components varied for the LEVs during a typical driving cycle. This study focuses primarily on emissions of black carbon (BC). These measurements allowed for the determination of BC emission factors throughout the driving cycle, providing insights into the temporal variability of BC emission factors during different phases of a typical driving cycle.
                    Cover page: Real-time black carbon emission factor measurements from light duty vehicles.
                    • Article
                    • Peer Reviewed
                    Recent Work (2018)
                    California's goal to reduce greenhouse gas (GHG) emissions to a level that is 80 % below 1990 levels by the year 2050 will require adoption of low-carbon energy sources across all economic sectors. In addition to reducing GHG emissions, shifting to fuels with lower carbon intensity will change concentrations of short-lived conventional air pollutants, including airborne particles with a diameter of less than 2.5 µm (PM2.5) and ozone (O3). Here we evaluate how business-as-usual (BAU) air pollution and public health in California will be transformed in the year 2050 through the adoption of low-carbon technologies, expanded electrification, and modified activity patterns within a low-carbon energy scenario (GHG-Step). Both the BAU and GHG-Step statewide emission scenarios were constructed using the energy–economic optimization model, CA-TIMES, that calculates the multi-sector energy portfolio that meets projected energy supply and demand at the lowest cost, while also satisfying scenario-specific GHG emissions constraints. Corresponding criteria pollutant emissions for each scenario were then spatially allocated at 4 km resolution to support air quality analysis in different regions of the state. Meteorological inputs for the year 2054 were generated under a Representative Concentration Pathway (RCP) 8.5 future climate. Annual-average PM2.5 and O3 concentrations were predicted using the modified emissions and meteorology inputs with a regional chemical transport model. In the final phase of the analysis, mortality (total deaths) and mortality rate (deaths per 100 000) were calculated using established exposure-response relationships from air pollution epidemiology combined with simulated annual-average PM2.5 and O3 exposure. Net emissions reductions across all sectors are −36 % for PM0.1 mass, −3.6 % for PM2.5 mass, −10.6 % for PM2.5 elemental carbon, −13.3 % for PM2.5 organic carbon, −13.7 % for NO x , and −27.5 % for NH3. Predicted deaths associated with air pollution in 2050 dropped by 24–26 % in California (1537–2758 avoided deaths yr−1) in the climate-friendly 2050 GHG-Step scenario, which is equivalent to a 54–56 % reduction in the air pollution mortality rate (deaths per 100 000) relative to 2010 levels. These avoided deaths have an estimated value of USD 11.4–20.4 billion yr−1 based on the present-day value of a statistical life (VSL) equal to USD 7.6 million. The costs for reducing California GHG emissions 80 % below 1990 levels by the year 2050 depend strongly on numerous external factors such as the global price of oil. Best estimates suggest that meeting an intermediate target (40 % reduction in GHG emissions by the year 2030) using a non-optimized scenario would reduce personal income by USD 4.95 billion yr−1 (−0.15 %) and lower overall state gross domestic product by USD 16.1 billion yr−1 (−0.45 %). The public health benefits described here are comparable to these cost estimates, making a compelling argument for the adoption of low-carbon energy in California, with implications for other regions in the United States and across the world.
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