Ambient Gamma Radiation as an Atmospheric Indicator in a Remote Oceanic Island Environment: Long-Term Variability and Meteorological Controls

Ambient gamma radiation is a key component of environmental radiation monitoring and is strongly modulated by atmospheric and meteorological processes. This study presents a long-term analysis of near-surface gamma radiation measured in Ponta Delgada (São Miguel Island, Azores), integrating continuous observations from the Portuguese National Alert Network for Environmental Radioactivity (RADNET) with meteorological data. The dataset spans more than a decade and includes a documented instrumental upgrade in 2020, which introduced enhanced sensitivity and radionu-clide identification capability. Results reveal pronounced variability across daily, seasonal, and interannual time-scales. A clear level shift is observed after 2020, attributable to the instrumental up-grade rather than to physical environmental changes, while the temporal structure and seasonal phasing of the series remain preserved. Seasonal analysis shows higher gamma radiation values during autumn and winter and lower values in late spring and summer, consistent with precipitation-driven washout and boundary-layer dy-namics. Generalized Additive Models (GAMs) highlight precipitation, wind speed, and relative humidity as dominant meteorological drivers acting through non-linear rela-tionships. Overall, the results support the use of ambient gamma radiation as an atmospheric in-dicator of boundary-layer processes and meteorological modulation in remote mari-time environments, extending its role beyond routine environmental surveillance.