Synoptic-Scale Modulation of Surface O3, NO2, and SO2 by the North Atlantic Oscillation in São Miguel Island, Azores (2017–2021)

This study investigated the extent to which the North Atlantic Oscillation (NAO) modulated daily surface-level concentrations of ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2) on São Miguel Island, Azores, between 2017 and 2021. Using validated data from two air quality monitoring stations, São Gonçalo (SG) (urban background) and Ribeira Grande (RG) (semi-urban), we applied descriptive statistics, seasonal Pearson correlations, and robust linear regression models to assess pollutant responses to NAO variability. The results reveal a significant and positive association between NAO phases and O3 concentrations, particularly in spring and summer. NO2 levels exhibited a strong negative correlation with NAO during summer in urban settings, indicating enhanced atmospheric dispersion. In contrast, SO2 concentrations showed weak and inconsistent relationships with the NAO index, likely reflecting the influence of local and episodic sources. These findings demonstrate that large-scale synoptic drivers such as the NAO can significantly modulate pollutant dynamics in island environments and should be integrated into air quality forecasting and environmental health planning strategies in small island territories.