Aerosol aging and cirrus cloud modification from Canadian wildfire smoke transported to Europe in 2025 observed by EarthCARE

Wildfire activities across Canada have increased significantly in the last several years. Intense wildfires release large amounts of smoke aerosols that can be lifted into the upper troposphere and lower stratosphere, providing a large episodic source of carbonaceous aerosols, composed primarily of organic carbon and black carbon. These smoke particles can persist for weeks to months and be transported over long distances, whereby extending their atmospheric influence far from the source regions. Smoke particles can greatly impact the Earth’s climate directly by scattering and absorbing solar radiation and indirectly by modifying cloud formation and properties. During long-range transport, smoke aerosols undergo chemical and microphysical aging, which may alter their size, composition, optical properties, and ice nucleation ability. In addition, smoke particles in the high altitudes can act as ice-nucleating particles (INP) to trigger cirrus cloud formation via heteorogeneous nucleation, modifying ice crystal number concnetrations, particle size and cloud optical properties. From the end of May 2025, extreme wildfire outbreak in Canada lifted smoke particles up to the lower stratosphere that were transported across the North Atlantic to Europe. In this study, we paramerize the aging transformations of smoke aerosols by comparing their lidar ratios (= extinction-to-backscatter ratio) and particle linear depolarization ratios (PLDR) directly retrieved by ATLID (the ATmospheric LIDar) onboard the EarthCARE satellite along the transport pathway of the smoke plumes. To do so, we make use of the HYSPLIT forward trajectories to track the smoke plume evolving from fire locations. Furthermore, we derive the cirrus cloud PLDR from ATLID as well as ice crystal number concentration (Ni) and effective radius (Re) from the lidar-radar synergy combing co-located ATLID and CPR (the Cloud Profiling Radar). Finally, we are able to compare PLDR, Ni, and Re between disturbed cirrus clouds by smoke aerosols and pristine ones to identify the impact of smoke particles on cirrus clouds.