AIDA Arctic transport experiment (part 1): simulation of northward transport and aging effect on fundamental black carbon properties

Black carbon (BC) is a key atmospheric forcer due to its interaction with solar radiation and clouds. However, accurately quantifying and understanding the impact of atmospheric aging on BC properties and ra- diative forcing remains a major challenge. To address this, the AIDA (Atmospheric Interactions and Dynamics in the Atmosphere) aRCtic Transport Experiment (ARCTEx) project simulated BC aging under quasi-realistic Arctic conditions in the AIDA chamber. Four distinct scenarios were simulated based on reanalysis data, rep- resenting summer and winter conditions at both low and high altitudes, to capture the variability in BC aging processes in the presence of nitrate and organic matter precursors during Arctic transport. In the first part of the paper, we define the meteorological conditions characterizing northward transport under different scenarios and describe the technical solutions to simulate 5 d transport in the AIDA chamber. In the second part of the work, we assess the evolution of fundamental properties, including density, morphology, and mixing state, as observed during the aging process. The ARCTEx project demonstrates that large facilities such as AIDA can successfully reproduce environ- mental conditions, enabling a gradual aging process that closely follows the natural timescales observed in the atmosphere. Our experiments revealed that temperature strongly influences the aging timescale and the evolution of BC’s diameter, effective density, and coating thickness. Low-altitude scenarios exhibited rapid aging, resulting in fully coated, compact BC particles within 39–98 h, corresponding to 50 and 80° N, respectively. In contrast, high-altitude transport was characterized by slow aging, with limited coating and compaction, even after 115 h of simulation. These findings provide valuable insights into the temporal evolution of BC properties during Arctic transport. In forthcoming work, we will report the implications of this evolution for climate-relevant properties such as light absorption and activation as cloud droplets and ice crystals. Together, these studies aim to enhance the representation of BC aging in climate models, reducing uncertainties in Arctic radiative-forcing estimates.