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.