Evaluating Ground-Level Ozone Formation Sensitivity on the Eastern Coast of Australia via Analysis of Long-Term In Situ Observation Data

Knowledge of ground-level ozone (O₃) formation in the Southern Hemisphere is limited due to the lack of long-term in situ O₃ observations. Here, we analyzed the ground-based measurement data of O₃, formaldehyde (HCHO), nitrogen dioxide (NO₂), and benzene, toluene, and xylene (BTX) collected from 2011 to 2020 at two sites in eastern Australia, namely, Memorial Park and Springwood. Only HCHO at Memorial Park showed a statistically significant upward trend (0.19 ppb yr^-1). Compared with the sea-influenced air masses, the land-influenced air masses were observed to enhance all pollutant concentrations at two sites. According to the site-specific sensitivity of the O₃ to the HCHO-to-NO₂ ratio (FNR), the daytime formation of the O₃ at two sites was mainly in the volatile organic compound (VOC)-limited regime. When the long-term variability of NO₂ was weak, HCHO, particularly from primary emissions indicated by BTX, was observed to predominantly control the monthly FNR at each site over time. Our work underscores the importance of long-term in situ measurements in interpreting ground-level O₃ formation and potentially informs future O₃ studies in other areas in the Southern Hemisphere.