Chemical and size-resolved signatures of firework smoke in an urban atmosphere

Aerosol particles significantly influence atmospheric composition and urban air quality, yet episodic and non-conventional anthropogenic sources, such as pyrotechnics, remain less well characterized. These events can emit gaseous pollutants and fine particulate matter containing metals and organic additives, posing acute exposure risks in densely populated areas. This study presents an observational characterization of the atmospheric impact associated with the celebrations following the Italian football championship in Naples on May 23, 2025, providing a real-world case study of large-scale pyrotechnic and smoke-bomb use in an urban environment. Continuous monitoring from 22 to May 31, 2025 employed a High-Resolution Time-of-Flight Aerosol Mass Spectrometer with a Soot-Particle module and an Optical Particle Sizer. During the peak celebration night, major aerosol constituents increased rapidly. Chemical analysis revealed distinct pyrotechnic signatures, including pronounced chlorine enrichment, concurrent spikes in coloured-formulation metal tracers (Ba, Sr, Cu), enhanced hydrocarbon fragments, and smoke-bomb combustion markers. Elemental analysis indicated a shift toward less-oxidized organic aerosol, consistent with fresh primary-combustion input. Size-resolved data showed that PM mass increased primarily in the accumulation mode. In contrast, particle number increased most strongly in the submicron fraction, implying a dual exposure concern: elevated mass burden and fine-particle concentrations. Although total PM mass decayed rapidly, aerosol chemical composition remained perturbed. These findings demonstrate that large-scale pyrotechnic use creates acute, chemically complex pollution episodes with significant implications for urban air quality. Compared with another major fireworks event, New Year's Eve 2025 in Naples, the celebration exhibited a lower peak in PM2.5 but more persistent compositional anomalies, underscoring the need for integrated chemical- and size-resolved monitoring to assess episodic urban emissions beyond standard regulatory metrics. Unlike typical single-night fireworks, this multi-night, city-wide celebration represents a non-conventional pyrotechnic episode, in which mass concentrations recover quickly while aerosol composition and size properties remain perturbed for several days.