Diurnal and seasonal variability of ozone precursors across Arizona’s sun corridor
Robertson, M.1, Roychoudhury, C.1, Pan, K.1, Mirrezaei, M.A.1, Sorooshian, A.2, and Arellano, A.F.1
1Department of Hydrology and Atmospheric Sciences,
The University of Arizona, Tucson, Arizona
2Department of Chemical and Environmental Engineering
The University of Arizona, Tucson, Arizona
The desert southwest of the United States, particularly Arizona, presents a distinctive environment characterized by an arid climate and ongoing air quality challenges. The region’s primary air quality concerns are dust storms and exceedances of surface ozone (O3). Elevated ozone concentrations in the region are driven by interacting chemical and meteorological factors, including chemical precursors such as nitrogen oxides (NOx), volatile organic compounds (VOCs), as well as regional and transboundary transport. In this study we 1) Characterize the diurnal and seasonal evolution of tropospheric NO2 and formaldehyde (HCHO) over Tucson from April through September, using TEMPO and Pandora observations; 2) Quantify the strength and variability of ozone-precursor relationships (e.g., O3-NO2, O3-HCHO) across diurnal and seasonal timescales, and assess how these correlations change between instruments and observational contexts; 3) Investigate evidence of nonlinear ozone formation behavior, including how ozone responds to changes in precursor levels (e.g., δO3/δNO2, δO3/δHCHO), and how this sensitivity varies with time and season. We apply co-location, correlation, and regression analyses to integrate satellite total-column measurements (TEMPO), ground-based total column retrievals (Pandora), and EPA AQS surface concentrations to accomplish objectives 1-3. We find that tropospheric NO2 and HCHO across Tucson exhibit a distinct diurnal and seasonal structure, with NO2 peaking in the winter and at night, HCHO peaking during the monsoon with an enhanced vegetative response, and O3 peaking in the late spring and summer afternoons, trends which are consistent between column and surface observations with minor TEMPO overestimation. Ozone-precursor relationships systematically vary by time of day and season, with the strongest O3-NO2 correlations in the summer afternoon and the strongest O3-HCHO correlations when HCHO is observed with a 3-hour lag. Sensitivity analyses reveal pronounced nonlinear ozone formation, with seasonally shifting diurnal sensitivities that reflect changing chemical regimes and boundary layer dynamics. The observational datasets from ground-based networks and satellite retrievals provide a unique opportunity to examine how atmospheric chemistry and meteorology jointly shape air quality in this arid region and to advance a regional understanding that can support future scientific and policy applications.