Particulate matter pollution in an Alpine Valley: long-term trends, source apportionment using specific tracers, and the effect persistent inversion dynamics

Major urban areas in mountain environments are typically located on valley floors. Here, mountain orography drives peculiar atmospheric circulation conditions. Persistent thermal inversion conditions may also occur, strongly affecting air pollution. This study characterizes the particulate matter (PM) pollution in an Alpine valley (Valbelluna, NE Italy) and analyzes the potential effects of local meteorology. First, long-term trends (2008-2023) are investigated using 3 different approaches to detect the effects of past and recent regulatory efforts at local, regional, and national levels. Since most mitigation measures focused on mobile emissions (e.g., traffic restrictions), the effects of these policies are further evaluated through generalized additive models. Second, a detailed source apportionment of fine PM (PM2.5) in the major city of the valley (Belluno) is performed during a cold season, when higher PM concentrations are observed. Major chemical species and minor/trace elements are analyzed, including specific geochemical tracers for primary biogenic, secondary, and biomass burning aerosols. PM2.5 sources are identified and quantified through positive matrix factorization. Results indicate biomass burning as the major source (52% mass), followed by secondary aerosol (21%), biogenic PM (20%), traffic (4%), and resuspension (3%). The source contributions are then handled to account for the local meteorology through dispersion normalization. Acknowledgements Third, the possible effects of persistent thermal inversion events are investigated by assessing the inversion strength from temperature profiles measured at multiple weather stations located at different elevations. This research has been carried out within the PNRR research activities of iNEST (Interconnected North-East Innovation Ecosystem) funded by the European Union Next-GenerationEU (Piano Nazionale di Ripresa e Resilienza (PNRR) Missione 4 Componente 2, Investimento 1.5 D.D. 1058 23/06/2022, ECS_00000043).