Comparison of fresh and aged smoke particles simultaneously observed at the ACTRIS Potenza observatory

This study presents a detailed analysis of the optical and microphysical properties of biomass burning aerosols from two distinct smoke plumes observed on 16 July 2024 at the CIAO atmospheric observatory in Potenza, Italy. The lower layer corresponds to a local wildfire, while the upper layer correspond to  a long-range transported plume from Canada. The objective is to highlight significant differences in their characteristics and atmospheric impacts.

The local fire was characterized not only with lidar measurements, but with all the remote sensing instruments present in the observatory. The fire, ignited around 16:00 UTC approximately 2 km from the observatory, was detected within an hour. Ceilometer lidar and radar data showed that wildfire particles ascended to 3 km, where elevated humidity facilitated the formation of condensation nuclei, confirmed by a radiometer-observed peak in liquid water content. The ACSM (Aerosol Chemical Speciation Monitor) and aethalometer measurements show a significant peak around 20:00 UTC, which coincides with the deposition of the particles. The inversion results from lidar measurements revealed a low contribution of black carbon and fine-mode particles, consistent with incomplete combustion typical of small-scale fires. Furthermore, a strong dependence on humidity variations was observed, emphasizing the dynamic interaction between local fires and atmospheric conditions.

In contrast, the Canadian wildfire plume, transported at altitudes between 5.5 and 6.5 km, exhibited different characteristics. Due the complete combustion particles have a higher absorption properties. The lidar ratio at 532 nm exceeded that at 355 nm, similar with previous observations of aged wildfire plumes. During long-range transport, aging processes such as coagulation significantly altered the particles, increasing their effective radius. Microphysical analysis indicated the presence of larger, more absorbent particles compared to the local plume.

This study underscores the importance of integrating remote sensing and in-situ measurements to capture the lifecycle of wildfire events. The results reveal a great variability in smoke plume properties, which must be accounted for in radiative transfer models to accurately assess their atmospheric and climatic impacts.