Assessing urban air quality in the context of strict traffic restrictions: particulate matter concentrations,...

Vehicle emissions are recognised as one of the primary contributors to urban air pollution. This study investigates the effects of strict traffic restrictions and reduced industrial activity on air quality in Lisbon (Portugal) during 2020-2021. Variations in particulate matter (PM₁₀) mass concentrations, chemical composition, and source contributions were analysed under pre- and restriction periods. Daily mean PM₁₀ concentrations decreased by 32% during the restriction period. Chemical analysis included equivalent black carbon from fossil fuel combustion and biomass burning, water-soluble ions, and major and trace elements. Although anthropogenic emissions strongly influenced PM₁₀ mass concentrations and their chemical composition, meteorological and seasonal factors also played a significant role. Positive Matrix Factorisation analysis identified six PM₁₀ sources: industry, biomass burning, traffic, secondary inorganic compounds, soil, and sea salt. Traffic was the dominant source during the non-restriction period (37%), whereas sea salt became the main contributor during the restriction period (27%). This study provides novel insights into the combined effects of traffic restrictions and meteorological variability on PM₁₀ sources in a coastal urban environment, highlighting the importance of reducing traffic-related emissions to improve urban air quality.