In recent years, wildfire activities have progressively increased due to climate change and human activities, posing unprecedented challenges to environment and climate governance. The molecular diversity of reactive organic carbon (ROC) in wildfire plumes, coupled with its complex oxidation processes through interactions with atmospheric physicochemical mechanisms, significantly amplifies the complexity of plume impacts on regional atmospheric environments. Tracking and quantifying the evolution of ROC from wildfire plumes is crucial to describe the carbon footprints and hence the impact on climate and ecosystem. Here, A Eulerian-Lagrangian hybrid model, the Forward Atmospheric Stochastic Trajectory model coupled with Master Chemical Mechanism (FAST-MCM), has been developed to study fire plume evolution. The model errors and uncertainties are estimated based on a wildfire airborne survey organized by Enviroment and Climate Change Canada (ECCC). FAST-MCM is driven by the meteorological fields from the Weather Research and Forcast (WRF) model. MCM were further expanded to represent the chemical mechanism in wildfire plumes based on carbon mass and ·OH reactivity analysis. Transport and dispersion have been simulated through a Lagrangian approach whereas the chemical transformations have been solved within a Eulerian framework based on the expanded MCM mechanism. Dry deposition is also coupled in the model and estimated based on the properties of reactive species and surface. The photolysis frequencies needed for the expanded MCM are computed using Tropospheric Ultraviolet and Visible (TUV) Radiation Model constrained by the measurements. FAST-MCM model is initialized by the species concentrations from the airborne measurements near the fire source. This model was applied to the fire plumes observed from airborne measurement, in the first attempt to study the carbon closure and budget for ROC evolution in wildfire plumes during the first few hours of photochemical aging. Based on oxidation rates of ROC components, carbon transformation budget, and key chemical parameters (e.g., carbon number, oxidation state and volatility) in the expanded MCM, the spatial and temporal heterogeneity of ROC evolution were explored in great details in the wildfire plumes. The outcomes will provide scientific support for predicting environmental effects of biomass burning, enabling targeted emission control strategies, and clarifying pollution liability attribution.

wildfire,,reactive organic carbon,plume evolution,Eulerian-Lagrangian hybrid model