Seasonal and synoptic drivers of aerosol populations in the Po valley: implications for air quality

Atmospheric aerosols impact global climate and urban air quality. Depending on their properties, these particles affect Earth's radiative balance and pose serious risks to human health. In response, the World Health Organization has established air quality guidelines, yet many urbanized regions continue to struggle with exceedances. The Po Valley’s unique geographical and meteorological characteristics cause reduced ventilation and vertical mixing, which, combined to high anthropogenic emissions, lead to recurrent pollution episodes. This thesis analyzes a three-year dataset (2019–2022) of aerosol concentrations and meteorological parameters collected in Bologna. The objectives are to investigate the seasonal variability of aerosol regimes, to characterize the relationship between aerosol populations and atmospheric dispersive capacity, and to assess the potential implications of climate change on these dynamics. To achieve these goals, a two-level clustering approach was employed, combining Self-Organizing Maps and the K‑means algorithm. The analysis identified six aerosol regimes, ranging from clean background to severe stagnation episodes. The cluster frequency mirrors the atmospheric states typical of each season. A coarse-mode stagnation regime was identified, linked to specific events such as Saharan dust transport. The results demonstrate that the integration of advanced clustering techniques provides a powerful framework for characterizing recurrent urban aerosol patterns, offering deep insights into the atmospheric dynamics governing aerosol populations in Bologna. The identification of regimes sensitive to specific meteorological drivers lays the groundwork for assessing how future climate scenarios may influence the frequency and intensity of pollution episodes in the Po Valley. This study contributes to a better understanding of current aerosol dynamics and to the broader challenge of predicting air quality under a changing climate.