| 29 Jul 2026
Diurnal and seasonal variability of ozone-precursor relationships in a semi-arid urban environment
Abstract. The southwestern United States is characterized by arid meteorology, responsive vegetation, intense solar radiation, anthropogenic emissions, and dust events that shape regional air quality. Elevated ground-level ozone (O3) concentrations are a primary air quality concern, driven by interactions between chemical precursors, including nitrogen oxides (NOx) and volatile organic compounds (VOCs), and meteorological variables. We examine these dynamics over Tucson, Arizona, using a multi-platform correlation analysis of satellite total-column measurements from Tropospheric Emissions: Monitoring of Pollution (TEMPO), ground-based total-column and surface measurements from Pandora, surface measurements from U.S. EPA Air Quality System (AQS), and lidar-derived planetary boundary layer height (PBLH). We address three objectives: (1) characterize the diurnal and seasonal evolution of tropospheric nitrogen dioxide (NO2) and formaldehyde (HCHO), (2) quantify the strength and variability of O3-precursor relationships across diurnal and seasonal timescales, and (3) investigate evidence of nonlinear O3 formation behavior. We show that tropospheric O3 precursors exhibit distinct diurnal and seasonal trends with NO2 peaking during winter nighttime, HCHO peaking during monsoon summer with concentrations 2.5–3.7 times higher than non-monsoon periods, and O3 peaking in late spring and summer afternoons. The strongest O3-NO2 and O3-HCHO correlations occur during summer afternoons and when HCHO precedes O3 by several hours, respectively. Evidence of nonlinear O3 behavior emerges through seasonal shifts in diurnal correlation structure. PBLH-normalization improves column-surface agreement for NO2 but not HCHO. These results highlight the importance of meteorology-chemistry-emissions coupling and the need to implement various observational contexts when interpreting precursor observations for O3 mitigation.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
