An Examination of the Weekly Periodicity of Surface Ozone Concentrations in Tucson, Arizona
Ground-level ozone (O3) pollution in semi-arid regions like Tucson, Arizona, presents unique challenges due to the interplay of anthropogenic emissions, biogenic volatile organic compounds (BVOCs), meteorological conditions, and regional transport. While much of the research has focused on Phoenix, Tucson—the second-largest city in Arizona—has received comparatively little attention, despite experiencing similar O₃ levels amid rapid population growth.
This study provides a comprehensive 22-year analysis (2001–2022) of O3 trends in Tucson using a combination of ground-based monitoring data, satellite observations (OMI, TROPOMI), and meteorological datasets. The findings reveal no statistically significant long-term trend in O3 levels at upwind, urban core, and downwind monitoring sites, suggesting that annual variations are not meaningful over extended periods. However, spatial differences persist, with downwind sites exhibiting the highest O3 concentrations, while the urban core consistently exhibited the lowest, and upwind locations falling in between.
Temporal variations also highlight a shifting weekend-weekday effect. Over time, the weekend effect has weakened, particularly in urban core and downwind locations, due to rising weekday O3 levels coupled with decreasing weekend concentrations. Seasonal patterns further indicate that winter and fall are characterized by VOC-limited conditions, whereas spring and summer transition to NOₓ-limited regimes, influenced by monsoon-driven BVOC emissions. Despite a general decline in NOx emissions, O3 concentrations have increased during winter and fall, emphasizing the growing influence of regional background O3 and persistent biogenic VOC contributions.
OMI and TROPOMI data (2001–2022) corroborate localized NOx reductions but also highlight an increase in VOC emissions during monsoon months. These findings underscore the need for targeted air quality strategies that consider seasonal chemical sensitivity, biogenic emissions, and regional transport in semi-arid environments.