Airborne characterization of black carbon properties in fresh and aged wildfire plumes over southern France

Black carbon (BC) is a significant short-lived climate forcer due to its strong absorption of solar radiation. Quantifying its radiative effects is challenging due to the ageing-induced evolution of BC mixing state and its impact on BC light absorption. Open biomass burning in the form of wildfires is the dominant global source of BC. In the summer of 2025, Europe experienced record-high wildfire emissions, while Canada faced its second-highest annual total carbon emissions. During this period, southern France was impacted by both several major local wildfire outbreaks and long-range transport (LRT) of dense smoke plumes from Canadian wildfires. Our study assesses the BC properties measured in different plumes, allowing their characterization in both relatively fresh emissions from southern France and aged air masses transported from Canada. Observations were conducted using the Safire ATR42 research aircraft during SILEX, the first campaign of the European project EUBURN. A total of 15 flights were performed with simultaneous measurements of BC mass concentration using a Single Particle Soot-Photometer (SP2), CO, CO₂ and CH₄ concentration using a PICARRO gas analyser, and aerosol optical properties with a modified dual-wavelength airborne CAPS-PM_SSA monitor and a Nephelometer. Additionally, geostationary satellite products and chemical-transport-model simulations performed using the FLEXPART and MOCAGE models were used as auxiliary data to support the aircraft measurements. Interestingly, within the wildfire plumes, aerosol particle number concentrations reached up to 17,040 #/cm³, accompanied by extinction coefficients at 520 nm as high as 275 Mm^-1, highlighting the high aerosol load and pronounced aerosols-radiation interactions, potentially impacting the local to global radiative balance. The average values of the combustion source indicator (ΔBC/ΔCO) reflected a common signature attributed to biomass burning emissions (~7). Furthermore, the ATR42 in situ data with fuel type assessments revealed the dominance of flaming combustion, with modified combustion efficiency (ΔCO₂/ΔCO₂+ΔCO) values exceeding 0.9. The BC core size distribution exhibited a unimodal pattern, with peak diameters typically ranging between 184 to 210 nm. Ongoing analyses aim to examine the diversity of BC mixing states and the associated absorption enhancement in both local wildfire plumes from southern France and long-range transported from Canada.