Where do wildfire-related emissions travel? Transport trajectories of black carbon, organic carbon, and PM2.5 from Italian forest fires (2008–2024)

Forest fires are a major source of atmospheric pollutants, including fine particulate matter and carbonaceous aerosols, which significantly impact air quality, human health, and the climate. During intense fire seasons, wildfire emissions can exceed those from other anthropogenic sources and be transported over long distances. To identify regions most vulnerable to long-range wildfire pollutant transport, we first characterized forest-related events in Italy between 2008–2024 using the MODIS/SENTINEL-2 Burnt Areas product from EFFIS. Emissions were quantified with GFAS, and atmospheric transport was simulated using the HYSPLIT model, computing 72-hour forward trajectories at three vertical levels (0.5, 1.5, 3 km). Fire sources and transport pathways were clustered using DBSCAN, and representative trajectories and density maps were derived to identify dominant air mass patterns, validated using AERONET daily observations of Aerosol Optical Depth (440 nm). Fire activity in Italy was highly localized, with hotspots in Calabria, Sicily, central-southern Sardinia, and the northern mountain regions. Annual PM 2.5 emissions ranged from 0.3 to 2 kt and increased over time, with organic carbon (OC) contributing 60%–80% and black carbon (BC) less than 10%. However, GFAS detected only about 21% of observed fires, likely underestimating emissions. Southern Italy, although characterized by numerous low-intensity fires ( ∼ 300 kg BC/fire), contributes the highest cumulative emissions, with pollutants often transported southward over the sea, toward North Africa. Balkans are frequently affected by plumes from Campania. In northern Italy, pollutants from fewer but more intense fires ( ∼ 550 kg BC/fire) mostly remain local, though higher-altitude transport increases variability, potentially affecting up to 20 million people.