In the wake of the Hayli Gubbi eruption.

Explosive eruptions require rapid, observation-constrained estimates of ash and sulfur dioxide emissions for hazard assessment. We analyze the 23 November 2025 Hayli Gubbi eruption (Afar, Ethiopia) with WRF-Chem v4.8 and use backward trajectories seeded within TROPOMI aerosol index and sulfur dioxide ([Formula: see text]) plumes to reconstruct time- and height-resolved source terms. The trajectory-derived ash source term, scaled to 0.8 Mt, captures the main ash transport corridor and the timing of the coarse-mode enhancement observed by AERONET at Nizwa University (Oman). For [Formula: see text], a manually prescribed time-height scenario improves agreement with the TROPOMI plume relative to the first trajectory-based approximation. The simulation captures the large-scale [Formula: see text] plume geometry and shows moderate agreement with aerosol optical depth and aerosol middle height. The corresponding [Formula: see text] emission is ≈0.15 Mt. About 6% of the fine ash deposits within 28 h, including fallout to the southern Red Sea and Gulf of Aden. This study demonstrates a rapid, observation-constrained reconstruction for a single-eruption case study.