UC Davis

Air quality management has prioritized reducing anthropogenic nitrogen oxide (NOx = NO + NO2) sources to mitigate ozone and particulate matter pollution. This imperative, however, faces challenges in rural agricultural regions like the Salton Sea Air Basin (SSAB) in Southern California, which remains noncompliant with ozone (O3), particulate matter ≤ 2.5 μg/m3 (PM2.5), and particulate matter ≤ 10 (PM10) National Ambient Air Quality Standards (NAAQS). In-depth investigations, including seasonal, annual, and diurnal climatologies, were conducted to scrutinize meteorological and air pollutant trends in the SSAB. While interregional transport has influence on air quality in cities nearby the Mexican border and the LA basin, both ozone and PM2.5 exceedances in the Imperial Valley predominantly arise from local emissions during periods with low advection in the more urban regions of the basin, while the drying of the Salton Sea is more influential at sites closer in proximity to the sea. PM10 exceedances were shown to depend largely on elevated wind speeds.Notably, the research hypothesizes that soil NOx emissions, exacerbated by year-round agricultural production with over $2 billion in annual sales, contribute significantly to local air quality problems. The nitrogen stable isotope composition (δ15N) is proposed as a valuable tool for NOx source apportionment due to differences in mean δ15N-NOx values between anthropogenic and biogenic emission sources. For this reason, nitrogen stable isotopes (δ15N) from actively collected NO2 were quantified, and contributions to total NOx were estimated using a mixing model, incorporating the mean δ15N-NOx from each emission source and from the a priori source apportionment reported in the California Air Resources Board’s NOx inventory. These results revealed that soil emissions are a substantial source, representing 35% and 21% of the total NOx inventory for the Imperial and Coachella Valleys, respectively, or 30% on average for the entire air basin. These estimates indicate a tenfold underestimation of soil NOx emissions on average by the current California Emissions Projection Analysis Model (CEPAM), with the largest discrepancies observed during spring and summer, periods of substantial biogenic activity. Crucially, this study adopts a community-engaged approach in collaboration with Comité Cívico del Valle and Western Service Workers Association, two influential community organizations that were instrumental in developing my community-based participatory research skills. Two dedicated sections within the dissertation delve into the comprehensive community engagement strategies employed, emphasizing inclusivity, local knowledge integration, discussion of successes and struggles, and participatory decision-making processes. Furthermore, the research documents a transformative mural art project co-created with community members at Sacramento’s Southside Community Garden, illustrating the intersection of environmental science and public art in conveying complex environmental issues to diverse audiences. Through a collaborative paint-by-numbers event, residents actively contributed to the artistic process, fostering a sense of ownership, and understanding of how our food system impacts their daily lives. These projects strengthened my community engagement skills and allowed me to practice alternative methods for scientific dissemination. This inclusive methodology enhances the broader impact of the research, creating an empowering relationship between academia and the local community.