Long-term analysis of carbonaceous fractions of particulate at a Central Mediterranean site in Italy

Several research efforts were devoted to investigate long-term trends of carbonaceous aerosols in atmospheric particulate matter. Carbon is known to affect climate, human health, and cultural heritage being an important component also for planning future policies. This work investigates the longest dataset of carbon content (EC and OC) in PM_2.5 and PM₁₀ fractions available in south Italy (2015–2022). Equivalent black carbon (eBC) was determined hourly in PM₁₀, using the multi-angle absorption photometer (MAAP), and it was used to evaluate the trend of the mass absorption coefficient (MAC) determined in-situ. PM_2.5 and its OC and EC content showed a statistically significant decreasing trend throughout years, since 2017–2018, approximately −5 % yr⁻¹, falling in the ranges reported for other urban background sites in Europe. The decrease of PM₁₀ and its carbon content was more limited, approximately −2 % yr⁻¹ but it was not statistically significant (p > 0.05). Temporal analysis revealed that seasonality played the most significant role in concentration pattern of PM and carbonaceous species, including secondary organic aerosol (SOC) and EC/OC ratio, compared to weekly or daily variabilities, with the highest daily values in winter/autumn. This was likely due to the contributions of biomass burning (for domestic heating and agricultural practices) and of road traffic both larger at this site during the autumn/winter. The value of MAC in-situ was 12.4 ± 1.2 m²g^-1 (as geometric mean ± standard deviation) or 12.6 ± 2.5 m²g^-1 (as arithmetic mean ± standard deviation), showing a slight increase during summer and early autumn compared to the other season. MAC showed an increasing long-term trend of 2.5 % yr⁻¹.