Analysis of the spatial-temporal variability of PM2.5 mass and fine-ultrafine particle concentration in two sites of Southern Italy

Within the framework of the TOX-IN-AIR Project, two simultaneous measurement campaigns were conducted during cold and warm periods at urban site, MAGA, and suburban background sites, ECO, in Lecce (Puglia, Southern Italy). Daily PM 2 . 5 samples were collected on quartz filters using a dual-channel low-volume automatic sampler (2.3 m 3 /h, SWAM - Fai Instruments). Concurrently, particle number concentrations in the 0.3-10 μm range (large fine particles) were measured using optical particle counters (OPC, Fai Instruments), while size distributions in the 0.01-0.8 μm range (ultrafine particles) were obtained with scanning mobility particle sizers (SMPS, Tropos and Grimm). Results showed comparable temporal variability of daily PM 2 . 5 mass concentrations between the two sites, with combined mean concentrations of 15.7 ± 9.4 μg/m 3 during the cold period and 14.0 ± 4.3 μg/m 3 during the warm period. Despite similar temporal trends, the urban site consistently exhibited higher ultrafine particles number concentrations than suburban site, approximately 36% higher in winter and 32% higher in summer, reflecting a stronger influence of vehicular traffic emissions. Both sites recorded higher particle concentrations (>25%) during the cold period, mainly attributable to biomass and wood combustion for domestic and residential heating, in addition to traffic-related emissions. The fine particle fraction followed a similar seasonal pattern, with ∼35% higher concentrations in winter. No statistically significant differences (p = 0.35) were observed for coarse particles (3.0-10 μm). A weak correlation between PM 2 . 5 and ultrafine particles number concentration, r = 0.42-0.70 at MAGA, 0.41-0.43 at ECO, indicates that reductions in PM 2 . 5 mass concentrations do not necessarily correspond to lower ultrafine particle exposure. Therefore, PM 2 . 5 levels alone are not fully representative of population exposure to ultrafine particles.